ASTR QB K58 N27 1990 * 2 º F--- c. | º -- º sº...º.º. - d : | - & Fº 2. zºº º º • - f * ſº lºſ W. ºl) & 2 Zºº &A * * c - | w ºn cººf wººt sº..."º || º -- | º sº º ſº tº $ lºº. It l | | • * 4. º º is * º wº - - & 9. º E. | tº º $º º * . 1. ** * * . i. º, , , 4% ºf º º 7 d 3, …" ~ As º 'º º ſº. A sº * º % | ſ Mº ſº Nº. - swº | ſº º -** *-*-****-º-º-º- =mºmº-TIF ſº- Qº º º º * ºf ſ *** -. 6 f t; & * | I . . . . ſº % #. º: .. º: # T . # º ºse sº wº * * ſº º 2 .” " v ſº ºf . Fº º, º º s: - ºr " º º . *- : W. º.º: ſº . . º: d º º tº: º غ Žº. º: %. º Q ºvs ... tº º Sºº ź * \,, *śsº USER'S MANUAL FOr The NRAO 12m Millimeter-Wave Telescope KITT PEAK, ARIZONA AUGUST 1990 EDITION |º º The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under nº cooperative agreement with the National Science Foundation USER'S MANUAL FOR THE NRAO 12 m MILLIMETER-WAVE TELESCOPE KITT PEAK, ARIZONA AUGUST 1990 EDITION The flónal Radio Astronomy Observatory is operated by Associated Univefsities, Inc., under cooperative agreement with the National Science Foundation. //2 % Mailing Address: National Radio Astronomy Observatory / // %O Campus Building 65 . 949 North Cherry Avenue Tucson, Arizona 85721-0655 Telephone: (602)–882–8250 12 m Telescope (Kitt Peak, Arizona), telephone: - (602)-620–5370 Credits: Cover design by the University of Arizona Graphics Art Department. The sketch was based on photographs by Mark Hanna (NOAO) and Mark Gordon (NRAO). THIS DOCUMENT IS PRINTED ON RECYCLED PAPER. 33: 2y+4 - PREFACE Our intent with this manual is to provide a general reference book for use of the NRAO 12 m millimeter-wave telescope. We have included basic material required for first-time use of the telescope, as well as more detailed information of possible º to all observers. We recommend that first-time users read Chapter 1 (Introduction), Chapter 2 (Getting Started), and the Visitor Information Guide before coming to the telescope. You may consult other chapters as needed. We are sure that there is room for improvement in this manual, and ask users to bring to our attention any errors, omissions, or unclear passages. So that we can provide updates when available, we want to keep record of the people who have copies of the manual. If you take a manual from the distribution box at the 12-m telescope or at other NRAO sites, please copy and fill out the address sheet on the next page and mail it to us in Tucson. Many people have contributed to this manual, and it is a pleasure to acknowledge them: Dave Hogg and Bob Brown wrote parts of Chapter 1 (Introduction), Chris Biemesderfer wrote a section of Chapter 5 (Source Catalogs), Chris Salter wrote an early draft of Chapter 6 (Continuum observing), and Al Wootten contributed material to Chapter 7 (Spectral Line observing). Much of the information on the FORTH system was taken from the 36 Foot Telescope Computer System Manual (Computer Division Internal Report No. 18) by J. M. Hollis. James Lamb, John Payne, and Antonio Perfetto contributed engineering drawings; George Kessler and Greg Morris drafted some of the figures. Darrel Emerson and Mark Gordon have provided numerous helpful comments. The 12 m telescope operators and observers made many suggestions and corrections to early drafts. Jennifer Neighbours has - suffered cheerfully through the editor's stylistic whims and through several versions of word processors while performing a most commendable typesetting job; her efforts are much appreciated. - On the following pages you will find a User's Manual Registration Form, Observing Application Cover Sheet, a Data Tape Request Form, and an observer's Comment Sheet. Please photocopy and use these as required. Philip R. Jewell Editor August 1990 iii NRAO 12 m TELESCOPE USERS MANUAL REGISTRATION SHEET (Please print or type) Name: Institution: Address: City: State : Zip : Country: Please mail to : National Radio Astronomy Observatory Campus Building 65 949 N. Cherry Ave. Tucson, AZ 85721-0655 USA PLEASE RETURN THIS FORM TO ENSURE THAT YOU RECEIVE UPDATESTO THE MANUAL National Radio Astronomy Observatory NRAO USE ONLY | 12-Meter Telescope/Arizona Operations Observing Application Cover Sheet Received: SEND TO: Director, NRAO, Edgemont Road, Charlottesville, VA. 22903-2475 - DEADLINES: 1st of Jan, July, Oct for the Spring, Fall, and Winter Periods, respectively. 1 Date: 2 Title of Proposal: 3 - Authors institution Who Will Grad otiºn. Anticipated Observe? Student? PhD Thesis? PhD Year 4 Contact Author for Scheduling - - 5 Telephones: Name/Address - Office: Home: 6 scientific Category: D atmospheric, C planetary, C solar, C stellar, C. galactic, C extragalactic 7 Mode: C spectra, C continuum, C other (specify): 8 Receiver 9 Ancillary Equipment: * - Units Units 10 Filters: G expander GºokHz, a lookHz a 250kHz, a sockHz à MHz #2MHz 11 Frequencies (include test lines): 12 Special Software? (describe on separate sheet) 13 Special Hardware? (describe on separate sheet) 14 Sessions/Days Requested: 15 LST Range: 16 Rossible conflict with Sun? (time of year to avoid) - 17 Abstract (do not write outside this space): Please attach a summary (of less than 1000 words) which contains the following information: 1) Scientific justification; 2) Observing strategy; 3) Source list with coordinates After your proposal is scheduled, the contents of this cover sheet become public information (supporting documents are for referees only). For Internal Use Only: - - REVISED 86 11 31 | NRAO 12-METER TELEscoPE DATA TAPE REQUEST FORM A copy of your raw data from the Analysis Computer will be archived on tape at NRAO Tucson for two (2) years. The archive tape will contain whole scans, individual records, keep data, and edited data. Effective 1 April 1985, there will be a charge of $11.00 plus $2.00 for shipping, if applicable, for each tape supplied to you by NRA0. The charges will be added to your meals and lodging invoice or billed separately. PLEASE COMPLETE THIS FORM BEFORE LEAVING THE TELESCOPE. The form should be left with Jennifer or Max at the Tucson office if you will be stopping by during business hours; if not, please leave the form with the telescope operator. The FORTH binary tape is the only tape that is immediately available at the end of your observing run. Analysis system (WAX) tapes require processing time; they will be mailed to you later at the tape charge plus $2.00 for shipping by least cost surface method. More than one file can be written on a tape depending on the size and BPI requested. All tapes will be FITS format unless otherwise requested. Please indicate below which tapes you want: FORTH binary tape [ ] (hand carried) Observing Initials Analysis System Tapes 1600 800 BPI BPI Raw Data [] Keep File [T] T [T] Edited Scan File É Individual Record File SHIP TO : BILL TO: Same [ ] OR Ship Surface [T] Extra Cost Method SPECIAL REQUESTS: Signature Date Revised 4/30/87 (Webb2) OBSERVER'S COMMENT SHEET National Radio Astronomy Observatory - 12-METER TELESCOPE Program: — Receiver: Date of Run: . Your Name: Phone: ( ) E-mail: In an attempt to assess whether observers on NRAO telescopes are experiencing any problems or dif- ficulties connected with their visits to the site, the Observatory is encouraging each observing team to complete this form and turn it in to the Site Director’s Office. You may wish to comment on our policies or procedures, and it will be especially valuable for us in our continuing concern for how we are handling the observing programs. The site director will send copies of this report to the Director’s Office and to any other individual(s) whom you may name, below. We will do our best to improve the operation, based on your suggestions. Thank you. How clear and complete did you find our user and data analysis manuals? How well did the equipment (including software) operate? How effective were the support services? Did you accomplish your scientific objectives? Observer: Please send the original of this sheet to the site Director who will then distribute it to the Director’s Office and to any other individuals whom you may name below. Others (by name): CHAPTER 1 INTRODUCTION 1.1 THE OBSERVATORY . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1.2 AN OVERVIEW OF THE OBSERVATORY . . . . . . . . . . . . . . . e º e e º e 1-2 1.2.1 THE SITE AND TELESCOPE . . . . . . . . . . . . . . . . . . . . . . . . 1-3 1.2.2 THE OPTICS . . . . . . . . . . . . . . . . . . . . . . . . . . - - - - - - - - - - - 1-4 1.2.3 THE RECEIVERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 1.2.4 LOCAL OSCILLATORS, THE I.F. SECTION, AND RECEIVER SELECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5 1.2.5 BACKEND SIGNAL PROCESSORS . . . . . . . . . . . . . . . . . . . . 1-6 1.2.5.1 SPECTROMETERS . . . . . . . . . . . . . . . . . . . . . . . . . 1-6 1.2.5.2 CONTINUUM BACKENDS . . . . . . . . . . . . . . . . . . . 1-7 1.2.6 COMPUTER SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8 1.3 OBSERVING CAPABILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9 1.3.1 SPECTRAL LINE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9 1.3.2 CONTINUUM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ". . . . 1-10 1.4 SYSTEM SENSITIVITIES . . . . . . . . . . . . . . . . . . . . . . e e e s e e o e s e o e 1-11 1.4.1 SPECTRAL LINE SENSITIVITIES . . . . . . . . . . . . . . . . . . . . 1-11 1.4.2 CONTINUUM SENSITIVITY . . . . . . . . . . . . . . . . . . . . . . . . 1 - 13 1.5 PROPOSAL PREPARATION AND SUBMISSION . . . . . . . . . . . . . . . 1-14 1.5.1 PROPOSAL REFEREEING . . . . . . . . . . . . . . . . . . . . . . . . . 1-14 1.5.1.1 SPECIAL POLICY FOR OBSERVATIONSBETWEEN 330-360 GHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14 1.5.2 PROPOSAL PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . 1 - 17 1.5.3 PROPOSAL AND OBSERVING PROPRIETY . . . . . . . . . . . 1-19 1.6 OBSERVATORY POLICY . . . . . . e < * * * * * * * * * * * * * * * * * * * * * * o e - 1 - 19 1.6.1 STAFF RESPONSIBILITIES . . . . . . . . . . . . . . . . . . . . . . . . . 1 - 19 1.6.2 OBSERVER'S RESPONSIBILITIES . . . . . . . . . . . . . . . . . . . . 1-20 1.6.3 MAINTENANCE AND REPAIRS . . . . . . . . . . . . . . . g º 'º º gº 1-20 ix ******** º - *_º º eºs.” º - & * ****** ** sº © & sºeºsºsºs º ***** *…* *.*.º.º.º.º.º.º.º. ºlº elº ****************** • * * * $ _&_& ******************************s’s’s’s & eºrº ****** e’sº © Tº e º 'º º ** 1.6.4 SHARING TELESCOPE FACILITIES WITH OTHER OBSERVING TEAMS . . . . . . . . . . . . . . . . • * * * * * * e o e e e 1-21 1.6.5 OBSERVATIONS UNDER POOR WEATHER CONDITIONS 1-22 1.6.5.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22 1.6.5.2 HIGH WINDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22 1.6.5.3 MOISTURE CONDENSING ON ANTENNA; FOG IN DOME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-22 1.6.54 BUILD-UP OF SNow OR ICE ON THE DOME ... 1-23 1.6.5.5 SUN ON THE DISH . . . . . . . . . . . . . . . . . . . • - - - - 1-23 1.6.6 OBSERVATIONS USING EMERGENCY POWER GENERATORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-23 1.6.7. SAFETY RULES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 1–23 CHAPTER 2 GETTING STARTED 2.1 WHAT TO BRING TO THE TELESCOPE . . . . . . . . . . . . . . . . . . . . . . 2-1 2.1.1 SPECTRAL LINE OBSERVATIONS ................... 2-1 2.1.2 CONTINUUM OBSERVATIONS . . . . . . . . . . . . . . . . . . . . . . 2-2. 2.2 START-UP CHECKLIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 2.2.1 GENERAL START-UP . . . . . . . . . © & © tº gº º go e º ſº e º º • & © e º º . . 2-3 2.2.2 SPECTRAL LINE OBSERVATIONS . . . . . . . . . . . . . . . . . . . 2-5 2.2.3 CONTINUUM CHECKLIST . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6 2.3 BASIC DATA REDUCTION COMMANDS . . . . . . . . . . . . . . . . . . . . . 2-6 2.3.1 STARTING THE REDUCTION PROGRAMS . . . . . . . . . . . . 2-6 2.3.2 CONTINUUM (CONDAR) COMMANDS . . . . . . . . . . . . . . . . 2-7 2.3.3 SPECTRAL LINE (LINE) COMMANDS. . . . . . . . . . . . . . . . 2-10 CHAPTER 3 INSTRUMENTATION 3.1 SITE PLAN ........... . . . . . . . . . . … . . . . . . . . . . 3-1 3.2 DOME FLOOR PLAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 33 TELESCOPE OPTICs .............. ... ſº º e º º ºs º g º O tº g º º g tº 6 @ & © tº º gº tº 3-1 3.4 SYSTEM ELECTRONICS ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4 3.5 RECEIVER ELECTRONICS. . . . . . • . . . . . . . . . . . . . . .. . . . . . . . . . . 3-4 3.5.1 90 - 1 16 GHz SIS MIXER RECEIVER . . . . . . . . . . . . • C g º º o o 3-4 3.5.2 200 - 250 GHz SIS RECEIVER . . . . . . . . . . . . . . . . . . . . . . . . 3-9 3.5.3 200 - 360 GHz SCHOTTKY MIXER RECEIVER . . . . . . . ... 3-9 3.5.4 EIGHT-BEAM, 1.3 MMSCHOTTKY RECEIVER . . . . . . . . 3-12 3.5.4.1 EIGHT-BEAM ROTATOR AND POSITIONING CONVENTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . 3- 16 3.54.1.1 ROTATOR CONTROL ANGLE . . . . . . . 3- 16 3.5.4.1.2 PARALLACTIC ANGLE . . . . . . . . . . . . . 3- 17 3.5.4.1.3 USER POSITION ANGLE . . . . . . . . . . . . 3- 18 3.5.4.1.4 POINTING AND MAPPING OFFSETS WITH THE 8-BEAM ROTATOR . . . . . . . . 3-19 3.6 THE LOCAL OSCILLATOR SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . 3–21 3.7 THE IF SECTION . . . . . . • * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 3–25 3.8 SPECTROMETERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–29 3.8.1 FILTER BANKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-29 3.8.2 HYBRID SPECTROMETER . . . . . . . . . . . . . . . . . . . . . . . . . 3-31 3.9 ANALOG CONTINUUM BACKEND . . . . . . . . . . . . . . . . . . . . . . . . 3-32 3.10 DIGITAL BACKEND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33 3.11 COMPUTER EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3–34 CHAPTER 4 TRACKING, POINTING, AND FOCUS 4.1 TRACKING CAPABILITIES ................................ 4-1 4.2 TRACKING LIMITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 xi * * * *I e º ºſe e.g. e. e. e.º. º.º. * *.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*_&_e_&_&_&_&_&_º ************************a*a*a*a*a*************a*a*a*a*a******************************s 4.2.1 ELEVATION LIMITS . . . . . . . . . . . . . . . . . . • - - - - - - - - - - - - 4–2 4.2.2 AZIMUTH LIMITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–2 4.3 TRACKING ERROR TOLERANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4 44 POINTING MODEL EQUATIONS ............................ 4-6 4.5 SUBREFLECTOR BEAM THROW . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 4-6 4.6 AZIMUTH AND ELEVATION POINTING OFFSETS . . . . . . . . . . . . . 4-9 4.7 POINTING ANALYSIS reogram & © e º 'º º e Q & © tº . . . . . . . . . . . . . . . 4-17 4.8 SEQUENCE of POSITION COMPUTATION OPERATIONS . . . . . . . 4–23 4.9 RADIAL FOCUS . . . . . . . . . . . . . ~ . . . . . . . . 4–24 4.10 LATERAL FOCUS . . . . . . . . . . . . . . . . . . . . ~ … 4–24 CHAPTER 5 SOURCE CATALOGS 5.1 INTRODUCTION ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.2 USING THE IBM PC TO ENTER AND TRANSMIT SOURCE CATALOG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . 5-1 5.2.1 MAKING A SUBDIRECTORY ON THE PC . . . . . . . . . . . . . 5–2 5.2.2 SOURCE CATALOG TRANSPORT MEDIA . . . . . . . . . . . . . 5-2 5.2.3 SOURCE CATALOG DATA FORMAT . . . . . . . . . . . . . . . . . 5–3 5.2.4 CREATING A SOURCE CATALOG ON THE PC . . . . . . . . . 5-4 5.2.5 TRANSFERRING A SOURCE CATALOG FROM THE VAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . e º 'º º e e º ºs & 5-5 5.2.6 TRANSLATING THE PC FILE INTO FORTH FORMAT . . . 5-6 5.2.6.1 SPECIFY CATALOG FILE NAME: -f . . . . . . . . . . . 5–7 5.2.6.2 SPECIFY FIELD ORDER: -r . . . . . . . . . . . . . . . . . . 5-8 5.2.6.3 SPECIFY FIELD DELIMITER: -d . . . . . . . . . . . . . 5-10 5.2.6.4 SPECIFY COMMENT IDENTIFIER: -c. . . . . . . . . . 5-10 xii 5.2.6.5 SPECIFY OUTPUT FILE . . . . . . . . . . . . . . . . . . . . 5-11 5.2.7 TRANSMITTING A SOURCE CATALOG FROM THE PC TO * FORTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12 5.3 GAINING ACCESS TO THE CONTROL SYSTEM FROM THE OBSERVER'S PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12 34 FORMAT OF THE SOURCE CATALOG ENTRIES.............. 5-15 5.4.1 EXPLANATION AND RULES . . . . . . . . . . . . . . . . . . . . . . 5-15 5.5 Typing A SOURCE CATALOG DIRECTLY INTO FORTH . . . . . . . 5-17 5.6 DELETING ENTRIES FROM A CATALOG . . . . . . . . . . . . . . . . . . . 5-19 5.7 PLANETS CATALOG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19 5.8 ENTERING POSITIONS FOR THE MOON, COMETS, OR SATELLITES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20 5.8.1 MOON POSITIONS . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . 5-22 5.8.2 COMET AND SATELLITE POSITIONS . . . . . . . . . . . . . . . . 5–24 5.8.3 USING THE PLANET, COMET, AND SATELLITE SLOTS FOR OTHER SOURCES . . . . . . . . . . . . . . . . . . . . . . . . . . 5–26 5.9 VELOCITIES OF PLANETS AND COMETS . . . . . . . . . . . . . . . . . . . 5–26 ENTRY . . . . . . . . . . . . . . . . . . . . • - - - - - - - - - - - - - - - - - - - - - - - - 5-27 CHAPTER 6 CONTINUUM OBSERVING 6.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 xiii * ºsºs * * * * s”sºe’s’s’s’s’s’sº-sºº's ****** 6.5 THE DIGITAL BACKEND . . . . . . . . . . . . . . . . . . . . . . . . . . o o e o o o e 6-6 6.5.1 DIGITAL BACKEND HARDWARE CONFIGURATION . . . . 6-6 6.5.2 SOFTWARESIGNAL PROCESSING OFDIGITAL BACKEND PATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8 6.6 OBSERVING PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12 6.6.1 POINT SOURCE ON/OFF OBSERVING PROCEDURES... . . 6-12 6.6.1.1 THE ON/OFF "SEQUENCE" . . . . . . . . . . . . . . . . . 6-12 6.6.1.2 DON-OFF, DON, AND DOFF . . . . . . . . . . . . . . . . 6-15 6.6.2 MAPPING EXTENDED SOURCES . . . . . . . . . . . . . . . . . . . 6-18 6.6.2.1 GRID MAPPING . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18 6.6.2.2 DRIFT SCANS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24 6.7 UTILITY OBSERVING ROUTINES . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26 6.7.1 THE FIVE-POINT MAP . . . . . . . . . . . . . . . . . . . 'e e o 'º e º e & 6-26 6.7.2 THE FOCALIZE . . . . . . e º e o e o e e e s e e s e e s e e e s e o e e s e e 6-30 6.7.3 SKY TIP PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . 6–32 6.7.3.1 THE SPTIPANALYSIS PROCEDURE . . . . . . . . . . 6–34 6.7.3.2 THE DIFTIP REDUCTION PROCEDURE . . . . . . . 6-37 6.7.3.3 THE STIP REDUCTION PROCEDURE . . . . . . . . . 6–39 6.7.3.4 STACKING MULTIPLE SPTIPS . . . . . . . . . . . . . . 6–43 6.8 CALIBRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6–43 6.8.1 DIRECT CALIBRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 6–43 6.8.2 HOT/COLD-LOAD CALIBRATION . . . . . . . . . . . . . . . . . . 6–45 6.8.3 CALIBRATION OF THE FLUX DENSITY SCALE . . . . . . . 6–52 6.9 CONTINUUM STATUS MONITOR . . . . . . . . . . . . . . . . . . . . . . . . . . 6-55 CHAPTER 7 SPECTRAL LINE OBSERVING 7.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7- 1 xiv. 7.4.1.1 THE PARALLEL/SERIES OPTION . . . . . . . . . . . . . 7-5 7.4.1.2 THE SPECTRUM EXPANDER . . . . . . . . . . . . . . . . 7-6 7.4.1.3 BAD CHANNEL ELIMINATION . . . . . . . . . . . . . . 7-8 7.4.2 HYBRID SPECTROMETER . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9 7.5 OBSERVING MODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10 7.5.1 POSITION SWITCHING . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10 7.5.2 ABSOLUTE POSITION SWITCHING . . . . . . . . . . . . . . . . . . 7-13 7.5.3 TOTAL POWER ONS AND OFFS . . . . . . . . . . . . . . . . . . . . 7-15 7.5.4 FREQUENCY SWITCHING . . . . . . . . . . . . . . . . . . . . . . . . . 7-16 7.5.5 BEAM SWITCHING . . . . . . . . . . . . . . . . . . . . . . . . . . • * * * * 7–22 7.5.6 MAPPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-24 7.5.6.1 MANUAL OFFSETS . . . . . . . . . . . . . . . . . . . . . . . 7–24 7.5.6.2 AUTOMATIC TOTAL POWER MAPPING OF RECTANGULAR GRIDS (TPM) . . . . . . . . . . . . . . 7–26 7.5.6.3 POSITION - SWITCHED MAPPING OF RECTANGULAR GRIDS (PSM) . . . . . . . . . . . . . . 7-30 7.5.6.4 AUTOMATIC MAPPING OF RECTANGULAR GRIDS BY CATALOG GENERATION (APM) . . . . 7-33 7.5.6.5 SPECTRAL LINE FIVE-POINTS . . . . . . . . . . . ... 7-36 7.6 CALIBRATION AND SIGNAL PROCESSING . . . . . . . . . . . . . . . . . . 7-39 7.6.1 VANE AND CHOPPER WHEEL CALIBRATION . . . . . . . . 7-39 7.62 DIRECT CALIBRATION ... . . . . . . . . . . . . . . . . . . . . . . . . 7–41 7.6.3 SIGNAL PROCESSING FOR POSITION AND FREQUENCY SWITCHED DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7–43 7.6.3.1 VANE/CHOPPER CALIBRATES . . . . . . . . • * * * * 7–43 7.6.3.2 NO-CAL SIGNAL PROCESSING . . . . . . . . . . . . . . 7-44 7.6.4 SIGNAL PROCESSING FOR BEAM SWITCHED DATA . . . 7-45 7.7 CHANGING THE INTERMEDIATE FREQUENCY . . . . . . . . . . . . . 7–45 7.8 USING THE OFFSET OSCILLATOR . . . . . . . . . . . . . . . . . . . . . . . . . 7-49 XV s &_&_&_*.*.*.*, * * * * * * * * * *, *-* *.*.*_e is &zº ************************************ ** e eje.*.*.*.*.*.*.*, 4 ºz º.º.º.e., s_º_e_s_s_&_s_&_*.4_4_** * * * * *.*.*.*.*.*.* * * * * ******************** s’e”s e’s eteº's *Tº sºº’ere e e°s’s ºsºe's * *sºº • * * * * * * * * * * * • - - - - - 7-51 APPENDIX A POINTING EQUATIONS FOR THE 12 M TELESCOPE A.1 PRIMARY POINTING EQUATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . A-l A.2 SECONDARY POINTING CORRECTIONS . . . . . . . . . . . . . . . . . . . . . A-3 VISITOR INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . • - - - - - - - - - - - V-1 I. OBSERVING OPPORTUNITIES AND RESPONSIBILITIES . . . . . . . . . . V-2 II. PROPOSALS FOR OBSERVATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . V-2 III. LOGISTICS OF OBSERVING AT THE 12-METER . . . . . . . . . . . . . . . V-4 A. THE ARIZONA ORGANIZATION . . . . . . . . . . . . . . . • e • * * * * V-4 B. TRAVEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-5 C. HOUSING ON KITT PEAK . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-5 D. MEALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-6 E. LAUNDRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-7 F. RECREATION AND LEISURE . . . . . . . . . o e o 9 e o e o 'o e e o e o o e V-7 G. CHARGES FOR ROOM AND BOARD . . . . . . . . . . . . . . . . . . . V-7 H. TELEPHONE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-8 I. LIBRARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • - - - - - - - - - V-8 IV. OBSERVING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-9 V. PUBLICATION OF RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-10 VI. NRAO TUCSON OFFICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-1 1 VII. NRAO REIMBURSEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V-11 A. TRAVEL REIMBURSEMENT . . . . . . . . . . . . . . . . . . . . . ... . . . V-1 1 B. NRAO SUPPORT FOR PAGE CHARGES: . . . . . . . . . . . . . . . . V-12 xvi. EQUIPMENT AND CALIBRATION STATUS I. INTRODUCTION . . . . . . . . . . . . . . . . II. RECEIVER STATUS . . . . . . . . . . . . . III. CALIBRATION STATUS . . . . . . . . . NRAO 12 M FRONT END BOX STATUS xvii xviii CHAPTER 1 INTRODUCTION 1.1 THE OBSERVATORY The National Radio Astronomy Observatory 12-meter telescope is a general purpose millimeter-wave observatory that supports spectral line and continuum observations in the atmospheric windows at 3 mm, 1.2 mm, and 0.9 mm wavelengths. The facility is located on Kitt Peak, Arizona, about 50 miles southwest of Tucson. The Observatory was constructed in 1967 with an original surface diameter of 36-feet (1.1-m). In 1982, the surface and backup structure were replaced with a 12 m diameter reflector. - The NRAO operates the telescope as a visitor facility, open to use by competent observers without regard to affiliation or nationality. Proposals are accepted before three deadlines each year and are evaluated by a panel of anonymous referees (see Section 1.5 for more information on proposal submission). The telescope is open for visitor use from approximately September 15th to July 15th each year. From late July, through the middle of September the prevailing weather pattern precludes observations at millimeter wavelengths and the telescope operation is shut down. Extensive overhauls, telescope upgrades and major maintenance are done during the summer shutdown period. The 12 m telescope is one of five observatory units operated by the NRAO. The NRAO is administered by Associated Universities, Inc. (AUI), under cooperative agreement with the National Science Foundation. Operations of the 12 m telescope are managed by the Site Director who, with the Deputy Director, also handles the scheduling of the instrument. The Site Director should be contacted with regard to general matters of operations policy and scheduling. In addition, more general questions or comments pertaining to Observatory-wide activities (scheduling procedures, scientific or instrumentation priorities, inter-site relations) or specific criticisms of, or suggestions for, the Tucson operation may be addressed to the Director of the NRAO located at the Charlottesville, Virginia office. 1 - 1 Table 1.1 Telescope and Site Statistics Site e: East Longitude: North Latitude: Elevation: Telescope: Primary Reflector Diameter: Focal Ratio (f/D) Prime Focus: Cassegrain Focus: Surface Accuracy (rms): Mount: Slew Rates Azimuth: Elevation: Pointing Accuracy (rms): Elevation Limit: Enclosure: - 111° 36' 51.12" = -7h 26m 27.41° 31° 57° 14" 1914 m (6280 ft) 12.0 m 0.42 13.8 75 pum rms Elevation over Azimuth 68°/minute 68°/minute 6" 15° astrodome with movable door and automatic tracking. Additional visitor information, including maps, lodging fees, travel reimbursement policies, and names of specific staff members responsible for operation of the telescope are described in the appended document, Visitor Information for the NRAO 12 m Telescope. 1.2 AN OVERVIEW OF THE OBSERVATORY This section provides an introduction to 12 m capabilities and supplies the basic information needed to prepare an observing proposal. Chapter 3 contains more detailed information on equipment and Chapters 4-7 describe observing techniques in detail. 1.2.1 THE SITE AND TELESCOPE Table 1.1 lists basic information on the observatory site and the telescope. Table 1.2 lists basic telescope efficiencies measured by the 12 m. staff. More details on telescope calibration are given in the appended document, The NRAO 12 m Telescope Equipment and Calibration Status. 1.2.2 THE OPTICS The 12 m uses "bent Cassegrain" optics. Following reflection by the primary, the beam is focused on a secondary hyperboloid mirror at the prime focus. From there, the beam is directed to a rotatable tertiary mirror at the vertex of the primary. This tertiary mirror directs the beam to one of four receiver bays. The position of the tertiary mirror can be commanded from the control room. Use of two or more receivers during a single observing run is possible. 12-meter Efficiency Factors Table 1.2 Frequency Beamwidth sº GHz (arc sec) 7A 7t ºfss ºlm 90 69 0.47 0.87 0.73 0.90 230 32 0.26 0.85 0.75 0.48 345 ce20 0.14 0.85 0.75 0.20 Notes: 7A = aperture efficiency, 7t. = rear spillover and scattering, blockage and ohmic loss efficiency, mtes = forward spillover and scattering efficiency, and "M’ = corrected main beam efficiency (percent power in the main diffraction beam relative to the outlying error beam). 1.2.3 THE RECEIVERS Table 1.3 lists the Cassegrain receivers available at the 12-meter telescope. A more complete description is given in the document Equipment and Calibration Status and in Chapter 3. 1.2.4 LOCAL OSCILLATORS, THE I.F. SECTION, AND RECEIVER SELECTION All receivers at the 12 m use phase-locked Gunn oscillators as the local oscillator source. For the high frequency receivers, the Gunn oscillator output is multiplied by solid state triplers or quadruplers. The tuning and phase-locking of the Gunn oscillators is remotely controlled from the control room. A single Gunn oscillator will typically tune over a 10 to 30 GHz range. 1-4 Table 1.3 Receiver Statistics Receiver Tuning Range Approximate Note Designation System Noise SSB 3 mm SIS 88-115 GHz 100–200 K. a 1 mm SIS 200–250 GHz 150 K. b 1 mm Schottky - 200–240 GHz 500–700 K c - - 240-270 GHz 900-1 100 K. 270–310 GHz 1100–1500 K. - 330-365 GHz 1600–2000 K. 1.3 mm 8-beam Schottky | 215-240 GHz 500–700 K. d Receiver Notes: (a) (b) (c) (d) The 3 mm SIS receiver is a dual linear polarization receiver, consisting of two superconducting mixers. The receiver is tunable between 88 and 116 GHz. For spectral line work the receiver is tuned so as to be inherently single sideband; for continuum work it may be tuned double sideband. The LO source is a Gunn oscillator. The liquid helium dewar must be filled every third day, a process that requires about one hour. . . . The 1 mm SIS receiver consists of dual polarization mixers in a 4 K, closed- cycle cryostat. The 1 mm Schottky receiver consists of four pairs of dual polarization Schottky mixers covering the 200–365 GHz range. A change between mixer-pairs involves rotating a LO diplexer and may require replacing the LO multiplier; the changeover requires about 0.5 to 1 hour. The LO sources for this receiver are Gunn oscillators. Normally, not all of the four mixer pairs are available at the same time; consult the staff for availability. The 8-beam receiver is configured as a 2 x 4 array of beams, with a beam separation of 85" between beams. The array can be rotated to an arbitrary orientation and can track parallactic angle in real time. The intermediate frequency of all 12 m mixer receivers is 1.500 GHz. The receivers in all four bays use a common, two channel I.F. processor module. The base-band output of this module is at 342 MHz. 1-5 Observers can select receivers in any of the four available bays automatically from the control room. The automatic selection process includes the routing of the LO reference signal, the I.F. signal, and the positioning of the central mirror. You can switch from one receiver to the other in as little as ten minutes, although more time is required if the receiver must be tuned. This capability makes it possible to observe with more than one receiver in a single observing run. (If you desire this capability, please state it clearly in your observing proposals, since not all receivers may be available at a given time.) 1.25 BACKEND SIGNAL PROCESSORS 1.2.5.1 SPECTROMETERS The spectrometers in routine use at the 12 m are filter banks. A new generation Hybrid Spectrometer, which is a combination of analog filtering and digital autocorrelation techniques, is now available for use. Table 1.4 lists the filter banks available. The multiplexer will provide two spectra with a total number of spectral channels not in excess of 512. Thus, it is always possible to record simultaneously the output of two filter banks. Except for the 30 kHz bank, all of the filter banks have two independent 128 channel sections. You can configure these banks in one of two ways. In the "series" option, the two sections are placed end to end in frequency space, i.e., the 256 channels are sequential in frequency. In the "parallel" mode, the two sections are used independently to accept different receiver (polarization) channels. The series mode is appropriate for observations requiring a large bandwidth. The parallel mode is useful for narrow band observations in which two different frequency resolutions are useful. Chapter 3 contains a more detailed discussion of filter bank configurations. Table 1.4 Filter Spectrometers Available Bandwidth of Number of Filter Banks Individual Filters Channels (filters) Available per Filter Bank 2 MHz 256 - 2 1 MHz 256 2 500 kHz 256 1 250 kHz 256 1 100 kHz 256 1 30 kHz - 128 l Spectrum Expander* - 256 l - *Series operation only. (See explanation in text.) *Uses the 100 kHz filter bank. Available resolutions are 25 kHz, 12.5 kHz, and 6.125 kHz. - - 1.2.5.2 CONTINUUM BACKENDS Continuum data at the 12 m is acquired by al two channel, four phase digital backend. A two channel analog backend continues to drive the on-line chart - recorders. The digital backend can record two switch phases and two calibration phases. The calibration phases can be generated by the synchronous emission of a noise diode, which is available at 3 mm wavelengths only. The start and duration of signal blanking (during subreflector chopping) can be controlled from the front panel of the digital backend. The data output of the digital backend is in the form of 32 bit words. The maximum number of digital backend data points that the control computer can record in a single scan is 54 ON/OFF REPEATS (216 samples) or 192 mapping points for a one or two channel receiver. The analog backends consist of phase-sensitive detectors that produce switched power and total power samples. The switched power and total power outputs are 1-7 recorded on a two-pen chart recorder (separate recorders exist for two-channel receivers). By convention, the switched power trace is recorded with a red pen and the total power trace with a blue pen. 1.2.6 COMPUTER SYSTEMS The 12-meter telescope uses two computers, a DEC PDP 1 1/44 for telescope control and data acquisition (written in the FORTH language) and a DEC VAX 1 1/750 for data reduction. A one-way data link carries the data acquired by the PDP-11/44 to the VAX where it is copied on the VAX's RA81 "analysis" disk. An IBM PC is available to observers to enter and transmit source catalogs to the control computer (see Chapter 5). The PC also serves as a terminal to the control computer; however, the need to interact with the control computer is very minimal and is confined to viewing or editing source catalogs. The telescope operator enters the observing parameters (frequency, integration time, and so forth) in the PDP-11/44 prior to each observation according to your instructions. You may - examine and reduce the data (line and continuum) as it is accumulated in the VAX. The data are entered into a set of personal data files whose file name extensions typically will be the observer's initials. The major files in this area are the PDFL file, containing the scan-averaged data; the IRFL file, containing individual spectral line samples, taken normally at 30 second intervals; the GZFL file, containing results for spectral line calibration scans; and the PKFL file, containing processed data, such as the average of all similar scans for a source, and the PAFL file which contains processed mapping data. Note that because of limited disk capacity the IRFL will hold perhaps 3 days’ data, and special action will be required to save a larger amount of individual record data. When you have finished your observations, the operator will make an archive tape of the observers’ files, and send it to the Tucson office. Using the town VAX 1 1/750, the staff will create an export tape of the type you requested (see the Data Tape Request Form in the Preface) and will mail it to your home institution. We 1-8 offer two types of export tapes. an ASCII tape following the FITS standard or a straight VAX BACKUP if you are using a VAX computer running the VMS operating System. During your observations, the FORTH control computer continuously writes a backup tape, known as the "FORTH tape." The FORTH tape and the VAX archive tapes are not the same for the following reason. For spectral line data the control computer transmits double precision (4 byte) integer quotients scaled by 20000 to the analysis system. Scaled single precision (2 byte) integer quotients are written on the control computer disk and binary tape. Furthermore, continuum data from the digital backend are not recorded at all. Thus, you are encouraged to use for your final analysis those tapes written from the analysis (VAX) system. 1.3 OBSERVING CAPABILITIES 1.3.1 SPECTRAL LINE The following spectral line observing techniques are supported at the 12 m (see Chapter 7 for more detailed descriptions): a) Position Switching -- The telescope moves between an offset - position (in relative or absolute coordinates). The spectrum is recorded as a ratio of (ON - OFF)/OFF. b) Total Power scans -- ON and OFF total power spectra are recorded separately for later processing into final spectra. The observer may take several ON Scans for each OFF. 1-9 e_º tº º, ø, º.º. * * * c) Frequency Switching -- d) Beam Switching + Position Switching -- e) Mapping -- 1.3.2 CONTINUUM The local oscillator is shifted by a few MHz at a rate of 5 Hz. The spectrum is recorded as a ratio of (SIG -REF)/REF. The subreflector is chopped at a rate of 1.25 to 5.0 Hz, and the telescope is repositioned at a prescribed rate (typically every 30–90 seconds). The spectrum is recorded as (ON - OFF). Total power or absolute position or frequency switched data are acquired while the telescope moves to automatically specified spatial positions. The following continuum observing procedures are supported at the 12 m; for more detailed information, see Chapter 6. a) ON/OFF's -- With the subreflector chopping, the telescope moves first to one beam position and then the other. Appropriate for point source observations. b) Mapping -- The telescope steps through a rectangular azimuth/elevation grid. Can be performed in switched or total power. "Dual- beam restoration" is available in the analysis stage. 1–10 Refereº 1.4 SYSTEM SENSITIVITIES The sensitivity of the telescope and receiver systems can be computed from the formulas in this section and the numbers in Section 1.2. 1.4.1 SPECTRAL LINE SENSITIVITIES The spectral line calibration technique generally used at the 12 m is the chopper wheel or vane method. The effective system temperature given by this technique includes corrections for atmospheric attenuation and antenna spillover, blockage, and ohmic losses. The method does not include a correction for error pattern losses as the error beam will couple differently to different sources. The effective system temperature, Tw." , on the scale defined above, is given by _ (1 + G /G) ITB. TA(sky)] 0.0 T : E mºmfssexp(-ſoº) sys where G. is the image sideband an. is the signal sideband gain; TRx is the receiver DSB noise temperature; - is the temperature of the sky (definition given below); 7t is the rear spillover, blockage, scattering, and ohmic efficiency; ºlfss - is the forward spillover efficiency; T., is the atmospheric optical depth at 1 airmass (the zenith); and, A is the number of airmasses, generally given by 1/sin(elevation). Tºky is given by the equation Tºky - miſm[1 - exp(-roA)] + (1 - m)T,pin + m,Tºgexp(-roA) (1.2) where TM is the mean atmospheric temperature, Tapill Tb is the spillover temperature, and g is the cosmic background temperature. The rms noise level for a given integration time, assuming equal integration time on the ON source and OFF source reference positions, is given by the radiometer equation T - ***. . (1.3) where Bril is the bandwidth of an individual channel in the spectrometer (in Hz), and - - t is the total integration time, including ON and OFF source time (in seconds). For observations of unpolarized signals with receivers that have two polarization channels, the two channels can be averaged to reduce the effective system temperature by - [...- ...-a -- ~-al’’’ 1.4 Tºys - r; in 2 + Ty.[2] 2 9 (1.4) where Ty,"[1] is the effective system temperature of polarization channel 1, and - - T..."[2] is the effective system temperature of polarization channel 2. 1.4.2 CONTINUUM SENSITIVITY Continuum observations at the 12 m are usually calibrated by a direct conversion of the measured antenna temperature into flux density (janskys). The scaling requires that the observer determine the atmospheric zenith optical depth, usually done with a tipping measurement. For a point source, the conversion is given by the standard equation 2kT - - sº- * exp(r.A) (1.5) mAAp W where k is Boltzmann's constant (1.380662 x 10^* J Kº"), TA is the measured antenna temperature with no efficiency or atmospheric corrections applied, 7A is the aperture efficiency, Ap - is the physical aperture (l 13.10 m” for the 12 m), To is the zenith optical depth, and A is the number of airmasses. The quantity 2k/Ar = 24.4155 Jy K* for the 12 m. A convenient measure of sensitivity for continuum observations is the rms flux density per root integration time outside the earth's atmosphere, So. The sensitivity achieved in a given integration time t and under an atmosphere with zenith optical depth ro, is given by S - S,tºº/* exp(r.A). (1.6) A table of So values for key frequencies is given below. Table 1.5 Continuum Sensitivities per Root Time Frequency So (per channel) S., (both channels averaged) (GHz) (Jy sºl/?) (Jy sºl/?) 90 1.5 1.0 230 6.0 4.0 345 - 48 (estimated) 34 1.5 PROPOSAL PREPARATION AND SUBMISSION 1.5.1 PROPOSAL REFEREEING Twelve meter telescope scheduling operates on a trimester system, with . proposal submission deadlines and their corresponding observing periods listed in Table 1.6. The intention of the 12 m proposal system is to insure that the projects granted telescope time are of current interest and that all proposals receive a prompt scheduling decision. Table 1.6 Proposal Submission Deadlines Deadline Observing Period - Receivers Available January 1 April to mid-July 3 mm, 1.2 mm July 1 mid-September to December 31 3 mm, 1.2 mm October 1 - January 1 to March 31 3 mm, 870 pum, 1-1.4 mm Proposals should be sent to the Director of the NRAO in Charlottesville, Virginia. After receipt by the Director's office, the proposals are assigned a reference number and are sent to a panel of five referees who are anonymous to the proposer and to each other. The referees rank the proposal as to scientific merit and possibility of achieving the scientific goal, recommend what percentage of the requested observing time should be granted, and make any comments they feel are pertinent. On the basis of the referees’ rankings and comments, the 12 m Scheduling Committee selects the proposals to be scheduled. A report of referees’ comments and the disposition of the proposal is sent to the proposal's contact authors, usually within 6 - 8 weeks after the deadline. Proposals for the 3 mm and 1.2 mm bands are considered for two consecutive trimester periods. On a proposal's second consideration, it will be in competition with new proposals received for that period. If a proposal is not selected on its second consideration, it will be declared inactive and generally will not receive any further consideration for telescope time. Proposals for the 870 pm (330–365 GHz) band are handled in a special way as described in Section 1.5.1.1. The 12 m Scheduling Committee will notify proposers as to the disposition of their active proposals after each selection process. After any evaluation of a proposal, the authors may submit an amended version of the proposal to address referees’ remarks or to otherwise strengthen the proposal. The proposal will be re-refereed for the next available period. Investigators are also free to withdraw a proposal and resubmit it as a different proposal. 1.5.1.1 SPECIAL POLICY FOR OBSERVATIONS BETWEEN 330–360 GHz Observations in the 330–360 GHz band are especially susceptible to weather effects. Since the programs can be scheduled only during the winter months each 1-15 year, observers often have difficulty completing their programs and then must wait an entire year to try again. To help alleviate this problem, we have adopted the following policy: Observations in the 330–360 GHz band will be scheduled only during the first quarter (January to April) of the year. If a high frequency proposal cannot be scheduled during this period, it will be dropped from the proposal queue, i.e., high frequency proposals receive only one consideration for scheduling. If a high frequency proposal is received at a deadline other than October 1 (for the January to April period), the proposal will be refereed at that time but will not be in competition for time before the January to April period. Each high frequency observing group will be required to submit, in writing, the details of a lower frequency (3 mm or 1.3 mm) backup program to be run in the case that the weather is not good enough for high frequency observations. The backup plan will be checked for conflicts with other observing programs in the proposal queue, but will not otherwise be refereed. These backup plans should be sent to the Tucson Site Director as soon as possible after the observers receive notification that their high frequency program is to be scheduled. If a high-frequency program is adversely affected by weather, the observers can apply to the Site Director for partial reimbursement of observing time, to be scheduled in the same quarter. It is the observers’ responsibility to petition the Site Director, at the conclusion of the initial observing run, for additional time. If we do not receive any notification, we will assume that the goals of the observing run were accomplished and we will not allocate any makeup time. A block of time will be reserved at the end of the high frequency observing season for rescheduling the high frequency observations. Up to 50% of the original time allocation could be rescheduled. If the high frequency backup time is not needed in its entirety, refereed, lower frequency proposals in the 1-16 queue will be scheduled during the block. We will attempt to arrange the scheduling so that repeat high frequency observers or the low frequency backup observers will have at least 3 weeks' notice of their observing time. 4. The reimbursement of observing time for weather problems applies to observations in the 330–360 GHz band only! 1.5.2 PROPOSAL PREPARATION All proposals should include a completed 12 m Observing Application Cover Sheet, an example of which is included as Figure 1.1. A blank copy of this cover sheet is in the Preface of the manual. The body of the proposal must include: a) A concise scientific justification for the project; (Do not exceed 1000 words.) b) An estimate of the observing time required; c) Frequencies and source coordinates to be observed. As a proposer, you should insure that the project is within the capabilities of the telescope, both in terms of available equipment and the sensitivities and integration times required. The telescope and receiver parameters given in Section 1.2 and the system sensitivities in Section 1.4 will be of use in estimating the required integration times. The most up-to-date information on these parameters is in the Equipment and Calibration Status document. The 12 m management imposes no hard rules as to the maximum or minimum lengths of observing programs. A typical 12 m observing run lasts 3 or 4 days of either partial or around-the-clock time. Requests for more than 5 days of time usually receive close scrutiny by the referees and scheduling committee. If only a specific LST range is required, you should request only that range. An observing session of less than a few hours may be unproductive because of the one-half to one hour of setup time typically required at the beginning of a run. 12-Meter Telescope/Arizona Operations Observing Application Cover Sheet Received: SEND TO: Director, NRAO, Edgemont Road, Charlottesville, VA. 22903-2475 National Radio Astronomy Observatory NRAO USE ONLY DEADLINES: 1st of Jan, July, Oct for the Spring, Fall, and Winter Periods, respectively. 1 Date: July 5, 1990 . A Search for Deuterated Molecules in the Bipolar Outflow sources 2 Title of Proposal: of Starburst Galaxies p Observations 3 Authors - institution Who Will Grad for Anticipat Jeremiah Peabody - Cactus State University - X - Hooty Saffe ticker § 9 X X X 2010 4 contact Author for Scheduling 5 Telephones: NamelAddress - * Dr. Jeremiah Peabody e office: 602–555-4897 Department of Astronomy & Applied Survival tº Cactus State University - Home: 602–555–6203 Dry Gulch, Arizona 86002 Secretary: 602–555-4814 6 scientific Category: C atmospheric, D planetary, C solar, D stellar, C. galactic, & extragalactic 7 Mode: spectra, CI continuum, C other (specify: 8 Receiver. 200–250 GHz SIS Receiver 9 Ancillary Equipment: None - Units • 10 Filters: G Expander, D 30 kHz, E 100-kHz, C. 250 kHz, D 500-kHz #g MHz # # 2-MHz 11 Frequencies (include test lines): 216. 113, 230.538 GHz 12 Special Software? (describe on separate sheet) None * 13 special Hardware? (describe on separate sheet) Hybrid Spectrometer 14 Sessions/Days Requested: 4. 15 LST Range: 0 - 24 16 Possible conflict with Sun? (time of year to avoid) Late November to late January 17 Abstract (do not write outside this space). We propose a program of seminal research into one of Nature's most perplexing problems, that of the creation of deuterium–substituted species in the bipolar outflow sources of starburst galaxies • We expect this project to keep us busy for years. Please attach a summary (of less than 1000 words) which contains the following information: 1) Scientific justification; 2) Observing strategy; 3) Source list with coordinates After your proposal is scheduled, the contents of this cover sheet become public information (supporting documents are for referees only). For Internal Use Only: - REVISED 8 FIGURE 1 - 1 SAMPLE PROPOSAL COVER SHEET For any proposal period, the Scheduling Committee almost always receives more proposals than can be scheduled; the requested time often exceeds the available time by factors of 2 – 4. For this reason, you should prepare proposals with care. 1.5.3 PROPOSAL AND OBSERVING PROPRIETY You are expected to confine your observations to those described in their refereed proposal. It is absolutely essential that observers consult with the Site Director or Deputy Director and obtain his approval before altering scheduled observing programs. Approval for changes can be granted under those circumstances that do not lead to an infringement on work proposed by others, and when the changes are in keeping with the spirit of the original, refereed proposal. These rules are fundamental to the integrity of the observing system at NRAO and are taken very seriously by the management. 1.6 OBSERVATORY POLICY 1.6.1 STAFF RESPONSIBILITIES The following is the responsibility of the NRAO staff: O To insure that the equipment needed for your observations is available and installed at the telescope. O To tune the receiver to the desired frequency. • To provide sound telescope pointing. O To provide you with fundamental telescope calibration parameters -- efficiencies, beamwidths, gain curves -- at standard observing frequencies. 1-19 O To provide advice on observing strategies, if requested. 1.6.2 OBSERVER'S RESPONSIBILITIES As a visiting observer, you have the responsibility for proper supervision of all aspects of the observing program. This includes: O Providing to the NRAO staff, well in advance of the time scheduled, a full description of the equipment needed for the observations as well as a complete list of frequencies to be observed. Usually this information is included on the proposal cover sheet. O To verify the telescope pointing and fine-tune it as needed. O To obtain all calibration and other receiver/telescope parameters necessary for data reduction. This can be done either by adopting or scaling the NRAO-provided information from standard frequencies, and/or by making the appropriate measurements. In either case, proper data calibration is your responsibility, not the NRAO's. O To inform the NRAO staff, before the observing period has ended, about the types of data to be written on an export tape for him, and the format of the export tape. - In addition, you are requested to provide feedback on the observing run via the "Observer’s Comment Sheet," available at the telescope, and in the Preface. 1.6.3 MAINTENANCE AND REPAIRS 1–20 One period each week is assigned to preventive maintenance and routine system tests. This period normally runs from 0900 MST to 1600 MST, and is most frequently taken on Wednesday. - If during a scheduled observing period a catastrophic failure of the instrument occurs which results in a loss of data, observations will be stopped and the NRAO technical staff will attempt to repair the equipment. In less serious cases where data-taking continues but where the quality of the data is not optimal, it is your responsibility to decide whether or not you wish to give up telescope time so that repairs can be made. - - Only the Tucson Site Director or, in his absence, the Deputy Director can make the decision to interrupt scheduled operations to make non-essential repairs. 1.6.4 SHARING TELESCOPE FACILITIES WITH OTHER OBSERVING TEAMS Since living quarters and work spaces at the telescope are limited, you should leave the mountain as soon as possible at the end of your run, allowing, of course, for a reasonable period of rest. If you wish to continue the reduction of your data sets, you should do so at the NRAO Tucson office, where a VAX 1 1/750 computer system identical to the analysis computer at the telescope is maintained. When two or more observing teams are sharing observing time, the team currently observing has priority to all telescope facilities, including computer usage. The other observing teams should endeavor to stay out of the control room and not interfere in any way with the ongoing observations. Unless one group of observers is declared the "prime observer" on the telescope schedule, equipment changes needed for a program will be done at the beginning of that program's time. 1-21 1.6.5 OBSERVATIONS UNDER Poor WEATHER CONDITIONS 1.6.5.1 GENERAL The operator on duty has the primary responsibility for the safety of the telescope, the dome, and the personnel in the dome. - 1.6.5.2 HIGH WINDS If the wind exceeds 15 mph, observations will be restricted to those quadrants where the telescope drive motor currents are not excessive. If the steady wind, or the average of gusty wind, exceeds 35 mph the dome door must be closed. Observations can be continued through the side of the dome. For winds above 45 mph, the dome door must be positioned 180° from the direction of the wind and held fixed. Observations can continue through the side of the dome, but the dome cannot be moved. If the wind exceeds 55 mph operations must cease and the telescope must be placed in the service position with the stow pins in place. - 1.6.5.3 MOISTURE CONDENSING ON ANTENNA; FOG IN DOME If there is fog in the dome, or if moisture is condensing on the antenna or equipment, the dome door will be closed. Observations can continue through the side of the dome. 1-22 1.6.5.4 BUILD-UP OF SNOW OR ICE ON THE DOME If there is a build-up of snow/ice on the dome, the accumulated snow/ice must be cleared from the dome door before observations can resume. 1.6.5.5 SUN ON THE DISH The pointing and focus of the dish can be seriously affected if the sun is allowed on the surface of the dish or the feed support legs. If accurate pointing is desired, care must be taken to keep the sun off the dish. To avoid excessive heating of the feed legs, the prime focus regions, and the cables to the prime focus, the dish will not be pointed to within one hour in right ascension or 15 degrees in declination of the sun. 1.6.6 OBSERVATIONS USING EMERGENCY POWER GENERATORS The telescope and dome have three sources of electric power – the commercial source and two power generators. Observations can continue as long as at least two of the sources are operational. If only one source of power is available, the dome door must be closed. - 1.6.7. SAFETY RULES The following safety rules obtain at the 12 m telescope site. We expect all observers and visitors to the site to read and abide by these rules. 1. To drive a GSA car, you must possess a valid driver's license. 1-23 10. 11. ******sºe”******** *_4_& * * ~ * sº º, º tº & sº e^e ºr 'e *.*.*.*, s” **.*.*.* tºº.” “...ºr ſº s’s Ye * - * *Tº º *...º.º.º.*.*.*.*s ºs ***************************************************sºsºsºsºsºsºsºs The Telescope Operator on duty is the only person allowed to operate the telescope. Observers are not to be on the telescope unless the duty operator has specifically authorized them to be there. Safety chains and rails have been installed at the entrance to the observing rooms. They are there to prevent you from walking into any possible pinch points or dangerous areas. Do not stand in the red areas because parts of the telescope and dome that move in those areas could injure you severely. Do not touch the yellow curtains around the inside wall of the dome. Behind them are exposed 480-volt lines. Please abide by all printed and posted safety rules such as "No Smoking" and "Do Not Enter This Area" posters, etc. Only the telescope operator or other qualified Arizona employees are allowed to operate the 'cherry picker'. Observers may ride in the cherry picker if authorized to do so by the duty operator. Hard hats are required for all persons in the dome area if someone is working above or in the cherry picker. The hats are located on the wall just outside of the observing room door. When walking outside to the dormitories or the lab at night, please be sure to carry a flashlight. You may encounter steps, drop-offs, or snakes. . The consumption of alcoholic beverages or illegal drugs is absolutely forbidden in the lab and telescope/control TOOII] area.S. 1-24 13. 14. 15. All employees and observers are required to wear seat belts while riding in government vehicles. Ice, rocks, and rock slides are frequently a hazard on the roads and walkways. Cattle and horses cross Highway 386 and several have been hit. Please drive and walk carefully. Please drive very slowly and carefully in all NOAO and NRAO parking or road areas. Pedestrians, including small children seem to leap out at cars on a regular basis. A more complete list of safety rules and recommendations is available in the observers’ lounge and from the telescope operator. You might find it interesting reading, although not required. 1–25 CHAPTER 2 GETTING STARTED 2.1 WHAT TO BRING TO THE TELESCOPE Your observations will be more efficient and you will achieve better results if you have thoroughly prepared for the run before arriving at the telescope. Most of this work should be done at the time the proposal is written (see Chapter 1). 2.1.1 SPECTRAL LINE OBSERVATIONS For spectral line observations, you should prepare the following before coming to the telescope: A) B) C) A source list with 1950 RA and Dec or (£ir, bir) Galactic coordinates, and the LSR velocities for each spectral line source. Keep in mind that the beam sizes for the 12 m can be quite small (20") at some frequencies so the positions should be appropriately accurate. If the source list is lengthy (say >30 objects), the observer can save time by typing the list prior to the run. This can be done in DOS text format and brought on 5.25" floppy diskette or typed into the VAX and transferred to the IBM PC. Otherwise, the positions can be typed into the PC at the start of the run (see Chapter 5 for the format of source entries). The line rest frequencies to an accuracy of 10 kHz. If emission lines are weak, test line frequencies should be included. The sideband choice, if the observations are being made with a double sideband receiver. The considerations for this choice include receiver tuning restrictions, the presence and location of lines in the image sideband, and the presence of atmospheric absorption lines. 2-l E) The observing mode. Options are i) position switching, ii) absolute position switching, iii) frequency switching, iv) beam switching, v) position switched mapping, and vi) total power mapping. The reference offset position, in angle or frequency, should also be considered. The filter banks and hybrid spectrometer, including the resolution and the mode of operation (series or parallel for filter banks). This decision hinges on the resolution and total bandwidth required. No firm rules exist, but the minimum resolution acceptable should probably give 3 – 5 channels across the line and the minimum bandwidth should have 10 - 20% of the band on each side of the line. 2.1.2 CONTINUUM OBSERVATIONS For continuum observations, you should prepare the following before coming to the telescope: A) B) C) The source list in 1950 RA and Dec or (£ir, bit) Galactic coordinates. If the list is long (say >30 sources), time can be saved by punching the list onto IBM cards prior to the run. Otherwise, the list can be entered into the control computer at the start of the run. The format for source entry is given in Chapter 5. Observing Frequency. For double-sideband observations, this is usually the local-oscillator frequency. If there is any possibility of spectral line contamination of the observations, choose an L.O. frequency such that no strong spectral lines lie in either receiver sideband. Observing Mode. Modes supported are switched or total power ON/OFF's, five-point mapping, azimuth mapping scans, or drift scans. Consider carefully the optimum beam separation for beam-switched observations. The default values are 4” at 3 mm wavelengths, and 2' at higher frequencies. 2–2 2.2 START-UP CHECKLIST Start-up checklists are given below for both spectral line and continuum observations. Although the Observatory staff tries to provide a fully functional system and advice about calibration constants and procedures, the responsibility for the integrity of the data rests with the observer. These checklists help insure that the system is configured properly and that variable quantities such as pointing and focus are properly set. Completion of these checklists may take an hour or more, but the time will be well-spent. 2.2.1 GENERAL START-UP The following checks should be performed first, whether the program is spectral line or continuum observing. 1. Prepare a source list on the IBM PC and transfer the catalog to the PDP 11/44 control computer. (See Chapter 5 for details.) 2. Have the operator tune the receiver to the desired frequency, including sideband and harmonic checks. This operation can often be done in parallel with item (1). - - 3. Ask the operator to load the continuum observing task (DBE) in the control - computer. Select a strong continuum source from the list of standard sources (see Chapter 4). A bright planet (i.e., Venus, Mars, Saturn, or Jupiter) is preferable. Pick one whose position is near the first program source, if possible. 2-3 Ask the operator to perform a Five-Point Map of the source to check for pointing offsets. Records of recent pointing offsets are kept on graphs near the observer’s console and can be used to estimate an initial value for the pointing. The operator will need to know the map grid spacing (called HP and usually set to 1/2 the beam FWHM) and the integration time per point. A detailed discussion of telescope pointing characteristics is given in Chapter 4. Data reduction commands for Five-Point analysis are given in Section 6.7.1 If the fit to the Five-Point is poor, repeat the map with updated pointing. Ask the operator to perform a "FocALIZE" on the source. This checks for the best value of the radial focus. The Focalize requires that you specify a first guess for the focus position (called F0) and the spacing between the focus settings (called WL). The operator or the "Friend of the Telescope" can tell you a reasonable first choice for F0 (usually around 42.0 mm). WL is usually chosen to be 1/2 the observing wavelength. (See Chapter 4 for more focus information and Section 6.7.2 for data reduction commands.) If the fit to the Focal IZE is poor, repeat the observation with an updated value of F0. Check the pointing offsets at another elevation. Pointing offsets depend strongly on elevation angle. If possible, check pointing on a low and high elevation source and enter the results on the pointing charts. Note Bene: Pointing and focus may change as the temperature of the dish (or parts of the dish) changes. Pointing and focus should be checked (at least) after nightfall and daybreak and more frequently if the dish is illuminated by the sun. 2-4 2.2.2 SPECTRAL LINE OBSERVATIONS The following checks are to insure that the receiver is tuned correctly, the spectrometer is properly configured, and the calibration scale is correct. If the program line is weak and no other strong lines are in the bandpass, tune first to a strong test line that is as close by in frequency as possible. "Strong" means any line that will produce a good signal-to-noise spectrum in a 5 - 10 minute integration, for example. Standard sources are listed in the NRAO Standard Catalog #1. (1 NRAO) If possible, use the same observing setup (same sideband, spectrometer mode, and observing mode) as will be used for the program observations. If the observations are of a common species, such as CO, there is no need to tune to another line. Perform a calibration scan and check for bad channels in the filter banks (see Section 2.3.3, notes 3 and 4). Report the bad channels to the operator, who will zero those channels in the control system software. Observe a test line in a strong source. Observers may wish to verify the sense of the velocity/frequency scale by shifting the rest frequency or center velocity by a small amount and seeing if the line moves in the correct direction for the sideband choice. If the observing setup is complicated, for example involving offset oscillators, take special care. Check that the temperature calibration is correct. This can be done by observing a standard source, presuming that the test line has known strength. 2.2.3 CONTINUUM CHECKLIST The continuum checklist is mostly completed in the General Start-up Checklist, particularly if the observations are to be ON/OFF's of point sources. If you will be making maps, observe a calibration source first, both to check the mapping algorithms and to establish beam-switching geometry and the calibration scale. 2.3 BASIC DATA REDUCTION COMMANDS Two other manuals, one for spectral line and one for continuum, describe the data reduction systems at use at the 12 m. These are available upon request. The discussion below is intended only as a quick reference list to help the observer get started. 2.3.1 STARTING THE REDUCTION PROGRAMS Before observations begin, the operator will set up a VAX disk subdirectory containing data files. This subdirectory is private to each observing team, and is denoted by [OBS. ini], where ini are the 3 letter initials of the lead observer. The data files in this subdirectory are also labeled with the same initials. If, when first sitting in front of the terminal, you find the - prompt symbol displayed, one of the reduction programs is currently running, probably left over from the last observer. Terminate execution of the program by typing EXIT. The screen will then display the $ prompt, indicating that the terminal is awaiting a VAX - command. Log out of the VAX by typing LOG. To log in to your own subdirectory, hit the ENTER key (carriage return), and respond to the prompt Username: by typing OBS. You will then be prompted for your initials, discussed above. If you are uncertain as to what subdirectory you are in, type SHOW DEF and the VAX will respond with the name of the area in the format [DIRECTORY. suBDIRECTORY]. The reduction program for spectral line data is called LINE and the continuum reduction program is called CONDAR. The LINE program can perform several basic continuum data reduction functions, such as a Five-Point Map display, Focus check display, and an ON/OFF sequence display. Hence, spectral line observers will probably not need to use CONDAR. - - - In the command lines below, a carriage return at the end of the line is implicit. To start the continuum program from the $ prompt, type conDAR You will be prompted to enter your initials. To start the spectral line program from the $ prompt, type LINE Again, you will be prompted to enter your initials. - N 2.3.2 CONTINUUM (CONDAR) COMMANDS You can execute some of the CONDAR functions listed below from the LINE program. When you can execute the functions from either program, they are w identified by "CONDAR" or "LINE"; otherwise, the functions execute only from CONDAR. The LINE commands are often slightly different from the CONDAR commands because of pre-existing commands of the same name. For data with two receiver channels, the scan number will increment by two each time a scan is taken. The first number (usually even) refers to Channel 1 and the second (odd) to Channel 2. - - 2-7 1. Five-Point Map Display Get the center scan number from the operator (it will be the final scan number minus 4 for two-channel data. Type - center_scan number F (CONDAR) center_scan number CF (LINE) . Display of ON/OFF Sequenc Type . - - - - scan number S (CONDAR) - scan_number CS1 (LINE) ) First load the STACK array with the scan numbers to be averaged. Do this by typing EMPTY scan number A - - - o add a single scan number to the stack, or º beginning_scan ending_scan ADD to add a range of scan numbers to the stack. (CONDAR only) for Channel 1 data, - (CONDAR only) for Channel 2 data, or CB (CONDAR only) for an average of Channel 1 and Channel 2 data. Both channels should be on the same calibration scale to use CB. 2.3.3 SPECTRAL LINE (LINE) COMMANDS The spectral line system always records data from two 256 channel filter banks. For each observation, the scan number will increment by two. The first number scan number (usually even) labels the first filter bank and the second scan number the Second bank. 1. To display a spectrum from the first filter bank, type scan number F 2. To display a spectrum from the second filter bank, type scan number S Note that the procedures F and S use the same scan number. If the scan is still in progress, the data transferred to that moment will be displayed. Note that in some observing modes such as frequency switching, no data are transferred until the end of the scan. - - To display the chopper wheel calibration array, called the "GAINS," type G1 for the most recent calibration scan in filter bank 1, or scan_number GGET XX for an earlier calibration scan. Similarly, to display a calibration scan for the second filter bank, type G2 Or scan number GGET XX where this time, the scan number is that associated with the second filter bank (= first filter bank scan number + 1). To eliminate a bad channel from a GAINS or spectrum, display the spectrum then type BADCH You will be prompted to enter the number of bad channels to be eliminated. Enter this, then move the vertical cross hair to each bad channel and strike any key but RETURN. At the end, this procedure will print out the channel number of each bad channel. The observer should report these to the operator, who will zero them in the control system software. To stack (average) scans, first load the stack array. Do this by first typing EMPTY to clear the array of previous entries. Then type scan number A to add a single scan number to the stack, or beginning_scan ending_scan ADD to load a range of scan numbers. To display an average of all data for the first filter bank, type C1 For the second bank, type C2 6. For an average of both banks, type CB Use CB only when the two filter banks are of the same resolution. To look at a scan in progress, type scan number Q1 for the first filter bank, or scan number Q2 for the second filter bank. These commands display the data transferred to disk up to that moment. 2-13 §§§ •I-I-I-Ie e_e a - - e, e s Is a T-I-T-IsIe e I*I*_-_-_*.*I*T* | *L-I-I e.e. < * : * : * ~ *.*.* ********************a*a*a********************************oºsºº"s"sºsºs","e"e"e CHAPTER 3 INSTRUMENTATION 3.1 SITE PLAN The 12 m is located on the southwest ridge of Kitt Peak, about two miles below the top of the mountain. Other telescopes on the southwest ridge are the NRAO 25 m VLBA antenna and the McGraw-Hill Observatory 1.2 m and 2.4 m optical telescopes. A drawing of the 12 m site layout is given in the Visitor's Guide. 3.2 DOME Floor PLAN Three rooms are available in the dome for observer use. During a scheduled observing time, you will normally want to sit in the control room at the observer's console so that you can communicate with the operator. An adjacent "breezeway" room has an additional computer terminal and a light table. A third room is available for work, data reduction, and private phone calls. This room has a couch that can be used for naps. If two observing teams are sharing time on the telescope, the data reduction station in the workroom is reserved for the team not currently observing. The team not currently observing should stay out of the control room if at all possible. If more than two observing teams are sharing time at the telescope, they should negotiate the use of the data reduction area in the lounge. 3.3 TELESCOPE OPTICS The 12 m employs "bent Cassegrain" optics for virtually all receivers used by visiting observers. A few test and special purpose receivers including the holography receiver are mounted at the prime focus. A diagram of the optics is given in Figure 3.1. The primary mirror is a 12.0 m paraboloid of 72 aluminum panels. The position of each panel can be adjusted by stand-off bolts. The subreflector (secondary mirror) is mounted at the prime focus and is supported by a quadrupod feed leg structure. 3-1 |12m OPTICS Nutating Subreflector - Diameter - 12m Primary Reflector . Focal Length - 5.08m F/D Of Final Beam – 13.8 • / - - 2–– Nauma, Mirror (1 of 4) Rotatable Tertiary Mirror Rotatable - Can Be Positioned To Any Tertiary Mirror One of Four Receiver Bays | RX l RX 2 FIGURE 3. 1 12-M TELEscoPE OPTICS The subreflector mounting box contains the nutation (beam switching) electronics and the solenoid drivers for the switching. The box also contains a gas discharge noise source and associated electronics. The feed horn of the noise source protrudes from a hole in the center of the subreflector. The subreflector is a machined aluminum hyperboloid, which has been shaped to compensate for aberrations and setting errors in the primary. The subreflector box is located in a Focus-Translation Mount with three degrees of freedom of movement. The subreflector can be moved in and out along the radio axis to adjust for radial focus changes, it can be moved in an "up-down" or "North- South" direction to compensate for North-South focus changes, or East-West to adjust for optimum azimuth position. The tertiary or central mirror is a rectangular flat mirror with azimuth and elevation position adjustments. The elevation position of the mirror is periodically measured and then clamped down. The azimuth position can be rotated to direct the radio beam to any of the four receiver bays, located behind the main reflector. The central mirror positioning is motorized and under servo control from the control room. Position readouts are available on the telescope or in the control room. The central mirror directs the beam to one of the four quaternary mirrors over each receiver box. The quaternary mirrors are oval flats and have one degree of freedom for position adjustment. The optics following the quaternary mirrors are contained within the receiver boxes and are usually different for each receiver. The alignment of the mirrors is done optically. Small optical mirrors are fixed to the tertiary and quaternary mirrors. A laser is mounted in the subreflector position and the mirrors are adjusted so that the laser beam spot is centered on the receiver lens. The beam also may be autocollimated at the subreflector to achieve the most precise alignment. 3-3 *...*.*.*.*_s_e_*.*.*.*.*.*.*.*.*.*.*.*.*.*_*_*.*.*.*.*.*.*.*.*.*.*.*_*.*.*_*.* ºº: º, sºfa.” ************** •,•: *ºº ſº. # * º e º & g|It ºf a * @I e º : * •,• - * **a*a*4. **.*.*.*, *.*.*, *.*.* *.*, jºezºe.º. :3: • *.*.*.*. ***************e” ************ &_& * * , º, º $ _º g & º e ſº e º e Iº e º & ºr ºf g_s = * * * * * * *_&_&_*.*_&_*.*.*I*_s_º sº e Tº eIsIt? Tº g * ************************************************************************* 3.4 SYSTEM ELECTRONICS A block diagram of system electronics for the 12 m is given in Figure 3.2. 3.5 RECEIVER ELECTRONICS All of the receivers in use at the 12 m are heterodyne mixers (sometimes called "coherent detectors"). Two types of mixers are used, Schottky barrier diodes and superconducting (SIS) junctions. A local oscillator (LO) signal is injected into the mixer or diplexed with the incoming radio frequency (RF) signal. The output of the mixer is an intermediate frequency that is the difference between the LO and RF signal frequencies. The Schottky mixers generally operate in a double sideband (DSB) mode, meaning that the IF signal corresponds to sky frequencies both above and below the LO frequency. The lower sideband (LSB) frequency visB = vio - vir. The upper sideband (USB) frequency is given by vusa = vio + vir. For continuum work, the sensitivity of the mixer is usually best in the double sideband mode. For most spectral line work only one sideband is of interest (exceptions to this do exist, particularly for detection work). Some of the SIS junctions used at the 12 m have tunable backshorts, which can be adjusted to resonantly cancel the unwanted sideband, and are essentially single sideband (SSB) mixers. A more detailed description of individual receivers is given in the following. 3.5.1 90 - 116 GHz SIS MIXER RECEIVER The 90-116 GHz SIS receiver is a superconducting junction receiver with two orthogonal linear polarization channels. The junctions are housed in a hybrid cryostat consisting of an inner, liquid helium dewar surrounded by a standard cooled, gaseous helium cavity. The junctions are attached to the exterior of the liquid helium dewar by copper heat straps or "fingers." The inner dewar is filled with liquid helium and 3-4 XOOTA WBLS/S WZI OVAJN (886 ! 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The liquid helium "hold-time" is about 3 days. About 30–45 minutes are needed to replenish the helium. The SIS junctions in use are niobium (Nb) based, and can be tuned to be single or double sideband. These mixers have tunable backshorts in the mixing cavity that can be set to reject the image sideband to 220 dB. A harmonic generator can be switched into the optical path for precise measurement of sideband rejection. The noise temperature is about 100 K. (SSB). Gunn oscillators are used as the LO source. A block diagram of the optics for the 90–116 GHz SIS receiver is given in Figure 3.3. A block diagram of the electronics for the SIS receiver is given in Figure 3.4. 3-6 Polarization Diplexing W Teflon Lens Teflon Vacuum Window N Beam From Secondary Low-Loss Foam Window T-H Wire Grid -/ ! Polarization Rotating Roof Top Reflector ~ 2TS [*==T_ J T L Corrugated Feed Horn Channel 1 Channel 2 SIS 90 – 115 GHz RECEIVER OPTICS (not to scale) FIGURE 3.3 +7 ° € ȘIHITOT J STENNWHO TVOILNEHO|| Z. HO | WVHSVIG XIOOTg , ! }|E|A|B|OB}} ZHS) G|| |-06 SISS\/18 OC] èJE||-||ToHWV -]]F LEJ SVD) / LWBH| ZHO 9° į-Zº ! SHEHITđWV ISOd | LE-ſ S\/DS) | | «-» «æ•••• •æ TLèJOHSX|O\/8 NIV/W |-|| Ol O— — -|–|—||—||— —{-, || 1ųoſsxova xºvTixov （Táxin SIS – + – –— — —{ |-30\/]LS XI#7 ••••••••-，«… --◄-►•••••••�）-，-，-，-）ſ-，-，-，•--- »•-，•-，•* --• æ-- →æ «-» «） • • • • • • •=====> w-， -） --→ ---- «-===） ---- «=） • → • → → → → • • • • •—•—• • → • • • •= (ZH0 GL1-06)r. NNOS) SVDS)dS (JEX|OOTG)- _~~ÝLLIT% C1BSWHd -£p Ç}}O_1\/[\NE]]. LV GJETIO? || NOO ÅTE LOWER} TENNWHO （JEHLO OL |T| |||| ||dvo | ||->|{e ºs e eIº e ---Y-I-I-I-T-I-T-I-T-Isle ºf eIsIºſe TABLE 4.4 - GPOINT MENU #2 -- PLOT SELECTION -1. 0. Return to data selection menu. No more plots -- terminate execution. Go to the plot option menu (laser printer and LSQ fits). Plot Delta-azimuth against elevation. Plot Delta-azimuth against cosine (elevation). Plot Delta-elevation against elevation. Plot Delta-elevation against cosine (elevation). Plot Delta-azimuth against azimuth. Plot Delta-elevation against azimuth. Plot Delta-Az, Delta-El pairs on an AZ/EL grid. Plot Delta-Az, Delta-El vectors on an AZ/EL grid. 4–20 TABLE 4.5 GPOINT MENU #3 -- PLOT OPTIONS 11. 12. 13. 14. Return to the plot selection menu. Make a copy on the terminal only (default). Make a copy on the terminal and the laser printer. Include a least squares fit of the data. Do not make a least squares fit of the data (default). Plot a full grid on the Tektronics (Modgraph) display. Turn off the full grid display for the Tektronics. Plot each source with a different symbol. Turn off Option 7. Plot up-arrows for rising sources and down-arrows setting SOUTCCS. . Turn off Option 9. Plot day/night data with different symbols. Turn off Option 11. . . Subtract a DC level from AZ/EL vector plots. Turn off Option 13. 4-21 OO | uoņD^9|E| 06 080/09 OGOț7 - 09`EO0 || | • • • • • • • • • • • • • • • •ſ• • • • • • • • § • • • • • • • • • • • • • • • • Q • • • • • • • • • • • • • • • • ! • • • • • • • •¿• • • • • • • • H • • • • • • • •q• • • • • • • •F • • • • • • •;“}”| -------+-------#-------+-------+-------+--------+-------{•*#:;-----+！ ● ● ● ● ● ● ●* • • • • • • • • • • • • • • • • + •|-• • • • • • • • •:-----{--------#------{E}|-----+---+------+------+------ 8;![]_+T）[] •-ș • • • • • • • •|- • • • • • • • • • • • • • • • • • • • • • • • •;&---->>~#fffſºi…---4-------|-------+-------|-------+------+------•{ __##-#ffffſ ſº-} |----O DJ ſēX- ?JB1||Hſ]ſº vİ###∞ →------|----e) ;------- <} {O· [] ------|-----48ſ főºſ------ Ğ©-|- LZOZ$ON *• þ || 0-0 Žy0 [] þæ • • • • • • • • • • • • • •*ſoro§ → • • • • • • •š• • • • • • • • B • • • • • • • •Ñ• .(H@}g\.?!........|.......ł.-ae | Ç@‘O F89|Zºo != 8 B// || F# 67.6°Z | | = \/ þæ• • • • • • • • • • • • • • • •ſ• • • • • • • • ► • • • • • • •• • • • • • • • • • • • • • • • • • • • • • • • • • • •* • • • • • • es eaeXxg"#E”Wț¢”)ţ“†”•A SuoņOĐJJOO Õuļļuļoeſ uoņD^9|E| O9 OS Oy O2 OZ O || O O 1 – O/ (oesoup) [3-olled 4.8 SEQUENCE OF POSITION COMPUTATION OPERATIONS The sequence of computer operations that is executed when seeking and then , tracking a source is as follows: a) b) c) d) e) f) g) h) Input RA-DEC (1950 or current) or Galactic Position; If 1950 position, precess to current date. A precession matrix is computed each day at 0 hours UT. This matrix is used to precess positions for the current day. The precessed position of a source is computed only when the source is first accessed. If source is a planet, interpolate to current UT. Do spherical coordinate conversion from RA-DEC to AZ-EL. Add azimuth and elevation encoder corrections as computed from Equations (A.1), (A.2), (A.7), and (A.8) (Appendix A). Add azimuth and elevation pointing corrections (see next section). Command telescope to the correct AZ-EL position. Loop to step (c) once per second. Between loops, extrapolate AZ and EL drive rates every 100 ms to compute positions. 4-23 4.9 RADIAL FOCUS To bring the incident radiation to a focus at the receiver feed horn, the subreflector (secondary mirror) of the 12 m may be moved in and out along the electrical axis of the telescope. The focus exhibits an elevation dependence which is automatically corrected by the control system computer, according to the equation F(E) - F. 2.8 sin(E) (4.1) where F(E) is the focus setting in millimeters, E is the elevation, and Fe, the subreflector focus setting at 0° elevation, is to be determined by the observer. Fe is given in millimeters, and larger values of F, represent greater distances between the dish surface and the subreflector. An automatic procedure called a FOCALIZE (this word really is in the dictionary!) exists in the control computer for determining the best value for Fe. An analysis routine of the same name exists in CONDAR and LINE for displaying and fitting the results. Instructions for performing a FOCALIZE are given in Chapter 6. 4.10 LATERAL FOCUS The position of the subreflector for optimum gain shifts in the elevation direction, with changing elevation angle. The change in antenna gain produced by this effect is not significant at 3 mm wavelengths but could be as much as 20% or more at 1.3 mm and shorter wavelengths. The 12 m is equipped with a lateral, "North-South" translation stage at the prime focus to eliminate this gain loss. The computer is able to control automatically the positioning of the stage, simultaneously applying an appropriate correction to the telescope pointing in elevation. This correction to elevation pointing is 34"/mm of movement of in the North-South focus Stage. 4–24 In the future, the coefficients necessary to control the movement of the North-South translation stage will be installed in the computer and applied automatically. At this time, the North-South stage is fixed in position. An automatic procedure for fitting for maximum North-South gain, called NSFOCAL is available. This routine operates analogously to the Focal IZE procedure. Normally, only staff astronomers use this procedure; we do not recommend that observers spend time trying to optimize this further. 4–25 CHAPTER 5 SOURCE CATALOGS 5.1 INTRODUCTION The control system supports five user-defined source catalogs of 34 entries each. In addition, the staff maintains seven in-house catalogs for standard pointing, calibration, and test sources. Visiting observers are not allowed to edit the in-house catalogs, but may edit the five user catalogs, subject to the following proviso: when two or more observing teams are sharing telescope time, each team should take care not to edit or delete the others' catalogs. Once an observing team has completed its run, its observing catalogs may be edited or deleted. As described in the following sections, you may prepare and transmit catalogs via a PC workstation or through a direct terminal session with FORTH. 5.2 USING THE IBM PC To ENTER AND TRANSMIT SOURCE CATALOGS To insulate 12 m users from the pain of entering source positions directly into the FORTH computer, the staff has developed or acquired programs for an IBM PC for editing, parsing, and transmitting ASCII source catalogs to FORTH. The PC is situated at the Observer's Console in the 12 m control room and can be used for catalog preparation, as a direct terminal to FORTH, as a terminal to the VAX, or in its native PC-DOS mode. The programs for parsing and transmitting source catalogs to FORTH have many capabilities and can handle a number of data entry formats. A complete description of these capabilities is given in NRAO 12-m Computing Report #16 (10 Feb 1989) by C. Biemesderfer. Much of the material in this section (5.2) is taken directly from that report, although not all the information in that report is repeated here. 5-1 5.2.1 MAKING A SUBDIRECTORY ON THE PC Before using the PC to create a source catalog, receive one from the VAX, Of transmit one to the FORTH computer, you must first create a subdirectory on the PC to hold your files. Presuming that the PC is powered up and booted, make your subdirectory as follows: Type NCD This is the NORTON Change Directory utility; it will display a tree structure of directories. - - Now use the arrow keys to toggle to a directory called USER. Type M This will allow you to make a subdirectory under USER Type in your observer initials (preferably the same used to set up your run on the FORTH computer and the VAX). Strike the ENTER key and you will be placed in your subdirectory and will be ready to enter or copy source catalogs. The staff requests that you use this PC subdirectory for all your PC work while at the telescope, whether related to source catalogs or not. - - 5.2.2 SOURCE CATALOG TRANSPORT MEDIA You can create your source catalog at the telescope or bring it with you from your home institution on one of several transport media including: 1. 5.25", 360k floppy diskette (DOS format) 2. 1600 BPI magnetic tape to be read on the VAX and transferred to the PC. 5–2 --_º -_-_-_ºxº-º-º-º-º---_-_-_*.*.*.* se *_º_-_º_-_-_-_-_-_º_*.*.*_-_--_-_º_ºzºº.º.º.º. w_-_-_-_* *_e_*.*.*_-_-_- º • 'º -- : ºº º-º-º-º-º-º: * - •"a". • *I-I- 4 º' * * • ::::::::::::::::::3::::::::::::::::::::::: s_e_*I - - - - - - - - “Is ---I-I-I-I - a. s. s. sºlº-I-I-I-Le. a Lº Te eI-I-I- - ***s o”eºsºsºsºsºe's ***********************a********************************* 3. Electronic transfer to the VAX over one of the standard networks. (If you desire this option, you must check that the transfer is possible before coming to the telescope!) 5.2.3 SOURCE CATALOG DATA FORMATS The parsing programs on the PC will accept a variety of source catalog input formats, then translate them into the rigid format required by the FORTH system. Here are the rules for the PC system: - 1. The program can identify 5 fields: source name, horizontal coordinate, vertical coordinate, LSR velocity, and an optional coordinate system identifier. The coordinate systems allowed are equatorial or galactic. 2. The fields can be in any order, although within a given file the order must be the same. The default field order is source name, right ascension, declination, and LSR velocity. 3. Numeric fields may be integer, floating point, or sexagesimal (for o, and 6). Sexagesimal coordinates must contain colons (:) to delimit hours (or degrees), minutes, and seconds. 4. A coordinate system flag may be specified in a file where the coordinate systems are mixed between equatorial and galactic. This flag is an integer field, where l indicates equatorial coordinates (the default), and 2 indicates galactic coordinates. 5-3 5. The fields (source name, coordinates, velocities) may be delimited by any character; blanks or tabs (any number) are the default. The source name field must never contain blanks, and (once again) sexagesimal coordinates must be separated by colons (:). 6. Blank (null) records and comment records are allowed. The comment character may be specified; # is the default. 5.2.4 CREATING A SOURCE CATALOG ON THE PC Several text editors are available on the PC for use in entering source catalogs. These include EDLIN, PCWRITE, vi, and the Norton Editor (NE). You may use which, if any, you are the most familiar with. All can be started from your user subdirectory. If you are not familiar with any of these, we recommend that you use the Norton Editor. This is a very simple, full-screen editor. A manual for this editor exists at the telescope, but you probably won’t need to consult it. To start the Norton Editor, type NE filename. ext (we recommend that you use . TXT as the file extension since . CAT is reserved for the ultimate, parsed file that is to transmitted to FORTH. Q The program will display a banner screen as it starts and will ask you to strike any key to begin entering source information. You can begin typing information at this point. When you are finished typing in your source catalog, strike the key F3 then E (for exit and save) If you need more information while editing, strike the F1 key. That displays the first help screen. Subsequent strikes of the F1 key will display additional help screens. These help screens will probably provide all the information you need, but if all else fails, you can read the manual (which is short). 5.2.5 TRANSFERRING A SOURCE CATALOG FROM THE VAX If your source catalogs are on the VAX, you will need to transfer them to the PC. To do this, create a subdirectory as described above, then type VTERM This starts the VTERM terminal emulation and file transfer program. Hit the ENTER key and you will get the VAX login prompt. Log into the OBS area and your subdirectory (designated by your observing initials). Your source catalogs should be in this subdirectory. Now type VTRANS This starts the file transfer system. The VAX prompt that appears will be WTRANS:- To transfer a file from the VAX to the PC, type at the VTRANS: prompt PUT filename. ext 5-5 The transfer will commence; when it is finished the PC will beep. Note that the file will be transferred into the current subdirectory on the PC, so you must be sure that you are in the correct PC subdirectory before beginning the transfer. VTRANS has many other capabilities. You probably won’t need these, but if you want more information, type HELP at the VTRANS prompt, or HELP VTRANS at the regular VMS $ prompt. When the transfer is finished, type EXIT to stop VTRANS. If you are finished with your VAX session, log off. At any time during your VAX session, or after you have logged off, you can toggle between the VAX and the PC by hitting the "hot key" sequence LEFT SHIFT - RIGHT SHIFT i.e., hit the two SHIFT keys simultaneously. 5.2.6 TRANSLATING THE PC F ILE INTo ForTH F ORMAT After you have created a source catalog in your PC subdirectory, you must then translate it into the FORTH "source card" format. This format is explained in detail in following sections for special case needs, but generally, you can let the PC do the work for you. If your source catalog is already in FORTH format (e.g., from a previous observing run), you can skip to the next section. The process of translating the arbitrary input file into FORTH format is called parsing, and the program that does this is called catparse. The format for catparse is catparse [-switch] [arguments] Il filter] [-output filename ] where all the quantities in [] are optional. The possible switches are —f specify the input file name (default: CATALOG.TXT) -r specify the order of the catalog fields (default: nrdv) -d specify field delimiter (change from the default: blanks) -c specify comment delimiter (change from the default: #) The switches and arguments are explained in detail in Computing Report #16. The case that arises most often at the telescope is: catparse -f input file >output file where myfile.txt is the input file in arbitrary format and myfile. cat is the output file in FORTH format. - - 5–7 --_-_- -I-T-I-T- º ---> -Y- ***** - ---- §: - •.º. eºsºs" 5.2.6.1 SPECIFY CATALOG FILE NAME: -f The default file name (catalog.txt) may be changed with the -f switch. An alternate filename can be specified by typing > catparse -f filename For example, if one wanted to parse the file ircmap. dat, the command line would look like > catparse -f ircmap. dat Note: The parsed output will be directed to the terminal screen unless you specify the S output redirection flag. 5.2.6.2 SPECIFY FIELD ORDER: -r The order of the fields or columns in the catalog file may be altered with the —r switch. By default, the fields are expected to be source name, right ascension, declination, and velocity. The field order is specified as a string of characters where each character represents a field. > catparse -r string The single character abbreviations for the various kinds of column are right ascension declination galactic longitude galactic latitude : SOUIICC Ila Iſle 5–8 • Yºº-ºººººººººº. •. - :*.*.*. sº. º. ſº tº - Tº Is Ie 2…" . . . . ~ *T*T*I*T* - a **s º.º.º. º: º: e 3. ºe º: º: º: e º º : *********************** 3:33:3: v source velocity w world coordinate system (WCS) flag x placeholder where nrdv is the default. For most catalogs, the WCS is assumed to be the same throughout the file and whether it is equatorial or galactic is determined by the appearance of the characters 'rd’ or 'lb’ in the record format string. For example, a catalog with columns in the order a, 6, source name, and velocity could be used by typing > catparse -r rdnv All the coordinates in the file are assumed to be ox, 6 pairs. Occasionally, one will have a catalog with coordinates mixed between equatorial and galactic systems. In order for such a catalog to be properly interpreted, each record must contain a tag field that indicates which WCS applies for the source position. The WCS flag is just an integer, where 1 signifies equatorial coordinates and 2 means galactic. The existence of this WCS flag field as well as its location in the record is indicated by a 'w' format specifier, as in the following examples: > catparse -r nrdwv Or > catparse -r nibww. Notice that is irrelevant whether the coordinates are specified as o.,6 or 2, b as long as their relative positions on the record are correct. Often, catalog files will contain extraneous information. (Well, extraneous as far as catparse is concerned.) Fields that should be skipped over in order to get to - other valid data can be marked with the 'x' format specifier. For instance, a catalog 5-9 that contains records giving source name, I magnitude, velocity, o,6, and o. and 6 components of proper motion could be parsed by typing > catparse -r nxvrd Note that it is not necessary to indicate the presence of data farther to the right on the record than the fields of interest (the proper motions in this example). 5.2.6.3 SPECIFY FIELD DELIMITER: -d The default field or column delimiter(s) may be changed with the -d switch. The default delimiter is white space, which means any number of blanks and/or tabs separate the fields. Several delimiters may be specified (as a single string), if necessary, but be wary of parsing consequences before getting too fancy. For best results, enclose the overriding delimiter(s) in double quotes. > catparse -d "delimiter(s)" For instance, if the fields in the catalog file were delimited by commas rather than white space, that would be indicated by typing > catparse - d "," 5.2.6.4 SPECIFY COMMENT IDENTIFIER: -c Comment records may appear in the catalog file. These records are identified by a special character in the first column of the record; by default, the # character signifies that a record is a comment and should be ignored by the parser. The identifying character can be changed with the –c switch. Only one comment character may be specified; for best results, enclose the character in double quotes. 5-10 > catparse -c "comment_identifier" If comment records beginning with 'I' were present in the catalog file, one would type > catparse - c "1" 5.2.6.5 SPECIFY ouTPUT FILE The output from the catparse program will be written to the terminal screen by default. Most of the time, you will desire that the results of the parsing run be - placed in another file that can be transmitted to the FORTH system. Such an output file is created by taking advantage of the output redirection feature of the operating system. A greater-than sign or right angle bracket followed by a file name will redirect any information normally written to the terminal into the named file. Typing > catparse -f sources. dat >sources. cat will parse the catalog sources. dat into the file sources. cat. The FORTH system will be slightly happier if your catalog entries are sorted, and a sorted output file can be created by using another feature of the PC's command interpreter, namely, that of piping output through a filter. The filter we are - interested in is SORT. The pipe character is 'I' and is used similarly to the redirection character. If one types > catparse -f sources. dat I sort >sources. cat one will wind up with a sorted catalog in the file sources. cat. If the output redirections were left off the above command, the sorted catalog would be displayed On the terminal. 5-1 l Before transmitting a catalog to FORTH, be sure that it has been translated into the proper FORTH format. Once done, type at the PC catxmit filename This will start a terminal session with the FORTH computer and loads the FORTH CATALOG program. Before doing the transfer, you will need to perform some setup operations including selecting a catalog, checking its current contents, and possibly emptying it. Follow these steps: 1. FORTH has 5 user catalogs, each of which can contain 34 source entries. These catalogs are common to all observers, so if you are sharing time on telescope with another team, you must coordinate the use of these catalogs. 2. The catalogs are addressed (i.e., pointed to) by typing In CAT where n can be 1, 2, 3, 4, or 5. ----- §§§ • ************a*a*a*a*a*a*a*a*a************************************************a*a*a*s List the contents of the catalog by typing INDEX You may delete the contents of a catalog by typing CLEAR BUT PLEASE MAKE SURE YOU ARE NOT DELETING SOMEONE ELSE'S CATALOG WHO IS STILL AT THE TELESCOPE. After an observing program is completely over, the catalogs for that program may be deleted. If you do not CLEAR the catalog, the transferred entries will be appended. If the catalog is already your own, this may be what you desire. Begin the transfer by typing CTRL/T i.e., pressing the CTRL and T keys simultaneously. You will see the contents of the catalog listed out. You can list your catalog again by typing INDEX Please proof them carefully, as transmission errors have been known to OCCUIT. To end your catxmit session, hit the ESCAPE key ESC 5-13 5.3 GAINING ACCESS TO THE CONTROL SYSTEM FROM THE OBSERVER's PC - The observer’s PC provides access to the FORTH system regardless of whether you are using the parsing and transmittal programs described above. There are two ways to gain access to FORTH from the PC. The first is through catxmit described above. catx.mit automatically loads the FORTH CATALOG module and expects to transmit a catalog. If you wish to start a simple terminal session with FORTH without transferring a catalog, you may do so by typing at the PC FORTH This starts a terminal emulation program similar to the VTERM sessions on the VAX. Please note that the only reason you would ever want to interact with the FORTH system is for catalog manipulation. The FORTH system is fragile and it is quite possible for the observer to crash the system by typing in the wrong thing. If you start a direct terminal session with FORTH, there are a few things you should know. The FORTH control system functions by loading specific modules into memory. The module that provides access to the source catalogs is called CATALOG. Anytime the system is rebooted or the spectral line or continuum tasks are loaded, the catalog module must be reloaded. Do this by typing CATALOG The loading process requires about 10 – 20 seconds. When (and only when!) the loading is complete, you are ready to enter or edit his catalogs using the commands given below. 5-14 5.4 FORMAT OF THE SOURCE CATALOG ENTRIES FORTH catalog entries must conform to one of the following three formats. Once again, you can save yourself the pain of this rigid format by using the PC parsing program described above. Still, you may need to know this format for entering single positions or for editing catalogs. Equinox 1950.0 Right Ascension and Declination: hh:mm:ss.s sadim:ss. EPoCH name Skk. k KM/S Current Right Ascension and Declination: hh:mm:ss.s Sdd: mm:ss. CURRENT name Skk.k KM/s Galactic (II, b11) coordinates: ddd. dddd sad. dddd GALACTIC name skk.k KM/s In the above formats, "S" signifies a sign digit (+); however, note Rule 5 below. 5.4.1 EXPLANATION AND RULES 1. The format of the source cards is rigid. The order and number of colons and decimal points, and the number of places after the decimal point is definite and may not be varied. In particular, do not forget the final decimal point on the declination specification. Failure to follow the format will result in incorrect source positions. Also, FORTH expects all commands to be in UPPER CASE letters. 2. Any number of spaces between words in permissible. ---------- Yº: - - *A* exº sexº ºil- º,\"." sº.” ** *** we" wº • rejevre The words EPOCH, CURRENT, GALACTIC, KM/S, etc., must appear literally (i.e., don't type '1950' instead of EPoCH; EPoCH tells the computer that the positions are 1950.0). The source name is limited to 11 characters with no embedded blanks. All alphanumeric characters and other standard ASCII characters such as '4', '-', etc., are allowed. Plus signs must not be used in the coordinates to indicate positive declinations or latitudes. Leave no blank spaces between a minus sign and its number: -10.0 not - 10.0 Leading zeroes may be included if desired. Equivalent entries are: 1:23:45.0 –2:34:56. 01:23:45.0 - 02:34:56. The source velocity is optional. If the velocity and the KM/s word are not given, a velocity of 0.0 will be set by the program. For spectral line. observing, the velocity should be specified in the source card, in general. Velocities are always given in units of kilometers/second. Velocity entries are interpreted in two different ways, depending upon the control system flag LOWVEL/HIGHVEL that is entered by the operator. LowVEL is the default mode. In this mode, velocities can be entered to an accuracy of 0.1 km/s and can range between the values -3267.8 and 3267.8 km/s. In the HIGHVEL mode, velocities ranging between -32678 and 32678 km/s can be entered to an accuracy of 1 km/s. In the HIGHVEL mode, the velocity format on the source card should include a decimal point but no trailing digit. Example: 15973. KM/S. Low and high velocity entries can be mixed in the same source catalog. They are not interpreted until the source is called up by the operator. If the source is to be interpreted with a high velocity, the operator must specify HIGHVEL before calling up the source. This flag will stay set until the system is booted or reloaded or the operator types LoWVEL. The observer should give clear instructions to the operator in this regard and should make sure that the velocities are properly interpreted. 5.5 TYPING A SOURCE CATALOG DIRECTLY INTO FORTH To enter a source catalog by directly typing on the terminal, follow the instructions given below. You can use the same process to make additional entries into an existing catalog. 1. Start the terminal session from the PC by typing FORTH The OK prompt should appear. Then type CATALOG 5-17 to load the CATALOG module. After 15–20 seconds, the OK prompt will reappear. Do not type anything before the OK prompt appears. Select a catalog in which to load the source list. To see which catalogs are empty, type Page to clear the screen, and In CAT INDEX where n can be 1 through 5. If your observing team is the only one using the telescope, you may empty any of the user catalogs by typing CLEAR after selecting a catalog with the 'n CAT” command. If you are sharing time with another observing team, do not empty a catalog without finding out which catalogs they are using. Leave the system pointing to the catalog you wish to use. You may also use catsmit to load additional Sources into an existing catalog, i.e., without clearing it. In this case, the additional sources will be appended to the previous list. Note: Never CLEAR an NRAO or PLANETS catalog. Enter the Sources according to the format given in Section 5.4. When finished, type PAGE INDEX to get a listing of the catalog. Proof the entries and if they are correct, type FLUSH This writes the catalog to disk. If this command is not issued, the catalog will be lost the next time the system is booted. 5.6 DELETING ENTRIES FROM A CATALOG The FORTH CATALOG program does not have any facility for editing errors in the source specification other than deleting the entire line and retyping it correctly. To do this, type FIND source_name DELETE where source_name is the source name of the entry. After any change to the catalog, remember to FLUSH it to disk. - 5.7 PLANETS CATALOG The Observatory maintains a catalog of planetary positions for the observer’s convenience. Planetary positions at 0° UT for each day of the year are stored in the control computer. The position of the planet at a given instance is computed from a three point parabolic interpolation of the positions at 0° UT for the current day, the day before, and the day after. At 0° UT each day, the telescope operator must load the planetary positions for that day. - - To get a listing of the planetary positions, Start the terminal session with FORTH by typing at the PC FORTH Then type cºeºsº s”.”. * *. • - x * •º".” - sº, •,•: * * *Releºs. º 'º e º ſº. - ... • *.*.*.*.*R-, -º-º-º-º-ººººººººººººººº Te º 'º' *_ºr_º_-_º_-_º & *a*a*a*s e *s **** "a a"oº"a"e"e"e"sºo"e"e"sºº"e"º, *_e_e_º - ...< *.*.*_º ****** - **** CATALOG if the FORTH catalog module is not already active, and after the "OK" prompt appears, type - PLANETS INDEX DATE A listing of the positions will appear followed by the date of the positions. A sample listing is given in Figure 5.1. The three positions for each object are the "yesterday," "today," and "tomorrow" right ascensions and declinations, with respect to the current epoch, in that order (the position on the same line with the source name is the position for the current day). The right-most column gives, from top to bottom, the horizontal parallax correction in arcseconds, the UTC for which the center position applies (always 0 for the planets), and the UNIT setting which told the FORTH system the appropriate data precision for the analog backend (this is no longer needed for the digital backend). The FORTH system uses integer arithmetic, and UNIT corresponds to the number of digits past the decimal place. The system cannot record more than four significant digits. 5.8 ENTERING PoSITIONS FOR THE MOON, COMETS, OR SATELLITES Positions for fast moving objects such as the Moon, comets, or satellites go into the PLANETS catalog and are handled in the same way as for the planets, i.e., the system makes a three point interpolation of positions at specific epochs. However, since these objects may change their positions very rapidly, the interval between - - epochs usually must be less than one day if the interpolation is to be sufficiently accurate. Intervals of 24, 12, 8, 6, 4, 3, 2, and 1 hours are supported. A special version of the program is available that will allow intervals as small as 15 minutes. You must also specify the data precision at the time the entries are made. 5-20 }~ { } ſy ºff- ~{ <-- Horizontal Par. (") <-- U.T. epoch of coords. <- "UNIT" scaling factor : º [[į №ſſº ºſ ſae) ſºſſſſſ！！) №ſſae) ~{ſº }ſ} {º}ſ^{ſ} ſ^{-{ſ} {V\，ſ}{z} where TA(HOT) and TA(COLD) are the apparent antenna temperatures of the hot and cold loads, respectively, and Tc(OLD_VALUE) is the old value of Tc that was in the computer during the hot/cold measurement. For each channel, there should be good consistency between the values computed via the computer and the voltmeter. If you are using a noise tube to calibrate the data, the calibration scale should stay fairly accurate even if the gain of the receiver changes slightly. If you are not using a noise tube, the To's and noise temperatures are accurate only at moment they are measured: receiver gain and tuning drifts will change these parameters. Depending on your choice of calibration methods, yOu may need to repeat the hot/cold measurements frequently. 6.8.3 CALIBRATION OF THE FLUX DENSITY SCALE For most continuum observations, the flux density scale is calibrated by observations of standard radio sources. In doing this, it should be remembered that, in addition to corrections for receiver and atmospheric effects, you should allow for the gain-elevation properties of the telescope if the observations cover a significant range of elevations. Current gain-elevation curves are given in the Equipment and Calibration Status document. 6–52 At millimeter wavelengths, the flux densities of most extragalactic sources are variable and we recommend the use of the planets or compact HII regions for calibration. At least at 1 mm, the brightest planets are usually significantly resolved. The peak flux densities of the planets should be computed using the PLANETS utility program available on the VAX. This program needs to know Effective observing frequency (GHz). • The telescope HPBW (arcsec). • The planetary unit semi-diameter (arcsec), i.e., the semi-diameter of the planet as seen from a distance of 1 AU, available from the Astronomical Almanac or Table 6.3. • The geocentric distance of the planet (A.U.), available from the - Astronomical Almanac. • The brightness temperature of the planet at this frequency. The result is given in Jy/beam. Table 6.3 gives the recommended brightness temperatures of the planets at 90 and 227 GHz. Most of these are taken from the work of Ulich and collaborators made with the 36 ft or 12 m telescopes. The 227 GHz temperature of Venus is interpolated from the measurements of a number of observers (Ulich et al., 1981; Werner et al., 1978; Whitcomb et al., 1980; Rowan Robinson et al., 1978), scaled to be consistent with the brightness temperature of Jupiter. Mars is not recommended as a flux density calibrator because its effective temperature probably depends on solar distance. 6-53 e_&_-_- äääß eſºs ſeleIsI-I-I4I4 º’s Isle ºe I-I-I-I-I-Iº.s. s.s., s_*I*-I-I-I-I*.*.*.*.*.*.*.*.*.*.*.*.* - - --- *********.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*************** Table 6.2 Planetary Flux Density Standards Planet Ts(90 GHz) Ts(227 GHz) snºe. . . . . .” (arcsec.) Venus 367 + 10 K. 317 it 30 K. 8.34 Mars” 207 it 6 K 207 it 7 K. 4.68 Jupiter 179 + 5 K. 165 + 18 K 95.20 Saturn 149 + 4 K. 140 + 14 K 78.15 Uranus 134 + 4 K 101 + 1 1 K 35.02 Neptune 127 it 4 K 104 + 1 1 K 33.50 * See note below. At 90 GHz, Ulich (1981, A. J., 86, 1619) suggests an effective temperature for Mars of - R O * . /2 * Ts (90GHz) - 206.8 #| K , (6.31) |- where, Ro is the Mars-Sun distance in A.U. Some other radio sources are expected to be non-variable, and in the case of HII regions, unpolarized. Three sources that make suitable flux density calibrators at 90 GHz are given in Table 6.3. 6–54 Table 6.3 Flux Density Calibrators Source - S(90 GHz) DR21 14.5 + 0.7 Jy W3(OH) 3.8 + 0.3 Jy 3C274(Virgo A) 6.5 + 0.3 Jy The flux densities of Table 6.2 are peak flux densities measured with the 12 IIl telescope. They are on the flux scale of Table 6.3. 6.9 continuuM STATUS MONITOR A sample continuum status monitor display is shown in Figure 6.12. The key to the display, line by line, is as follows: Lines 1 and 2 SCAN SOURCE HORIZON LST UTC DUT1 YEAR OBS OPR Current scan number Source name Time to 15° elevation (rise or set) Current local sidereal time Current coordinated universal time UT1-UTC time correction (top) year, (bottom) date : Observer's initials Operator’s initials 6–55 : fil. T |f| L OK §[CfA H {} | {}+ I] IJT 1 FIGURE 6 - 12 – – CONTINUUM MONITOR S CREEN SOURCE HORIZ || || LST UTC 1333 OBS OPE 5078 J.J.237 2 : º 3 12 28 EE 13 22 : 18 –5 13 14 UC T 3 ''S CIIC RC JR 3 , ſº |||{SIS R. fl. ITECL.IHF. TI () || fº ZIH || T H E L E ||f| TID || CIJRREHT 8 : 54 1*} , 1 2.É 1 [2]{3 EE . C 0 || ||{\ }|I) 2E3 53 49) : EE 13.5%) . [] 3 : E 1 : 57. 3 20 ! 17 | E3 . fºL T ||f||. 2E3 52 E1. 40 53 44. ºf ALFACT II. 205 - 3 1:24 35 - 32.É.3 ERROR -tº º 1 : 13 . -[3] : ºº ! :] 1 . |TFFSET tº i º) . Ø º, ºl [] FF 3ET –2 14 [3] : 37 FREſ] UEHC'ſ IF '3 L [] SE HT I]: F F [] IHT . –0 14. tº i º) 2 31 , E[][3][2][3] 100 1 2 l º + EEF, Hl 2 : ſº ſº i º) 1 . S 1273E 34 l£5E) tº * . 1. º —EEfºll –2 tººl tº tº 1 - 8723875E - - f* T || REFRT T( fl. HH J P J L 2 HP Fū Tf Jū TC : EFF 1 .52 52 sº 1E.8E § { {3}{2} ſº 35, E[] . E ſº . E8E E. E. 45. E. :) T[L FUCUS 8Fſ iſ J TFI U ) HODE SCAH3 SfâITFLE3 SEC TIME IHPUT d 10 E2.4 -º) , (3) 1 tº .3ſ) 33 E3 4 8 lº) . Ø 1 : 20 E1.5 0.01 0.3142 - 3 : 3 - (Far right) Receiver identification code Line 4-8. (Left side) CURRENT 1950. O ECLIPTIC OFFSET (Right side) COMMAND ACTUAL ERROR OFFSET Line 9 Apparent right ascension and declination of date RA and DEC at Equinox 1950 Source ecliptic coordinates RA and DEC offsets (RA in time units, DEC in angle units) Source azimuth and elevation (spherical coordinate conversion plus pointing corrections) Actual AZ/EL encoder readings Difference between COMMAND and ACTUAL Total AZ/EL offsets (sum of pointing offsets plus subreflector beam throw) - (will contain mapping offsets when a map) Lines 10–13 FREQUENCY I.F.'s LO SB NT DSF (top) Rest frequency, in GHz; (middle) First of 2 possible ~ 2 GHz synthesizer frequencies; (bottom) Second of 2 possible 2 GHz synthesizer frequencies - (top) Phase-lock loop IF (MHz); (bottom) First local oscillator frequency (MHz) Multiplier factor for the LO source Sideband code (0, 1, 2, or 3) Noise tube in use (1 = in use, 0 = not in use) Data scale factor (top — Ch. 1, bottom – Ch. 2) 6–57 Lines 14–16 ATM REFRT T(AMB) POLZ HP Fg TAUg TC $EFF: Lines 17–19 TOL FOCUS SP (V) TP (V) MODE SCANS SAMPLES SEC TIME AZ and EL pointing model corrections, mm:ss Subreflector +BEAM position (AZ and EL, mm:ss) Subreflector - BEAM position (AZ and EL, mm:ss) Number of airmasses (1/sin(EL)) at current elevation Refraction coefficient for elevation refraction pointing correction (") Ambient temperature (Celsius) Orientation angle of prime focus box (always 0) Beam half-width and half-maximum (used for 5-point mapping grids) Radial focus zero position (in mm) Zenith optical depth (nepers) Calibration scale factors (K) – (top — Ch. 1, bottom - Ch. 2) Aperture efficiency (in percent) Pointing tolerance mm:ss (top – input, bottom - actual pointing error, sum of AZ and EL) Actual radial focus at the current elevation (top - input, bottom - actual) Switched power voltage from analog backend (top — Ch. 1, bottom, Ch. 2) Total power voltage from analog backend (top — Ch. 1, bottom – Ch. 2) Observing mode (e.g., BS = beam-switching) Number of scans requested Number of continuum ON/OFF samples requested (top - total sample time requested; bottom - sample time remaining (top – total integration time requested for this scan; bottom – integration time remaining) 6-58 CHAPTER 7 SPECTRAL LINE OBSERVING 7.1 INTRODUCTION This chapter supplies basic information for setting up and executing a spectral line observation. Specific topics covered are • A start-up checklist; Choosing the observing sideband; Choosing and configuring the filter and Hybrid spectrometers; Observing mode options; • Calibration and signal processing options; Changing the effective intermediate frequency (I.F.); A key to the on-line status monitor display. Other chapters provide additional material important to spectral line observations such as hardware descriptions and pointing and focusing the telescope. 7.2 SETUP CHECKLIST Once the scientific goals of the observing session are clearly in mind, you must decide upon the equipment and observing techniques to be used. The decisions to be made and the options are listed below. a) . Sideband Choice. For double sideband observations, care must be taken in choosing the placement of the image sideband. b) Spectrometer Configuration. Filter bank spectrometers with several different resolutions are available. The observer must choose which to use and how they should be configured (the "parallel" or "series" option). 7-1 §§§ *_º ------, -, -, ---_-_-_-_&_º_43_48_&_&_&_-_- *****.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*. The Hybrid Spectrometer, which has numerous resolution and bandwidth options, is also available. c) Observing Mode. Choices are • Position Switching (with relative offsets) • Absolute Position Switching (fixed offsets) • Frequency Switching • Beam switching • Position switched mapping • Total power scans d) Observing Time "budget." Prior to the start of observations, you should make a rough budget of observing time requirements. In addition to the integration time on the program sources, you should budget time for "overhead" items such as telescope movement, and pointing and calibration tests. Before beginning program observations, check the telescope pointing and focus. A few observations of test sources are also advisable. These observations are discussed in Chapters 2, 4, and 6. 7.3 SIDEBAND CHOICE Most of the Schottky mixer receivers in use at the 12 m operate in a double sideband (DSB) mode, that is, they respond to two frequency bands separated by twice the I.F. Other receivers, such as the 3 mm SIS receiver can operate in a single sideband (SSB) mode and require upper sideband operation. For the DSB receivers, you can generally opt to place the program line in either the lower sideband (signal sideband below the LO frequency) or the upper sideband (signal above the LO). Equipment constraints, such as the tuning range of the local oscillator or the receiver, may sometimes determine the sideband. Other times, the presence of telluric lines -_-_-_-_* -_-_-_-_-_- - - e. e. ----- s w •º.º.º.º.º.º.º.º.•.” *L*L--_-_-_º_e_e_º_&_&_&_- *_º_º_-_-_ _-_&_&_**_º_º_-_º_-_º_º_e_e_º_&_&_& **********************a*s*************-****e’e”,”,"s"sºo"e"sºº" ūgūštº gº steer the choice. When you are free to choose the sideband, make the choice with Caſe. The primary things to watch out for when choosing the sideband configuration is the presence of "contaminating" lines from the image sideband. Consult a good tabulation of spectral lines such as the Lovas Catalog (F. J. Lovas, J. Phys. Chem. Ref. Data, 15, 251, 1986) to see what spectral lines are present in both the signal and image sidebands. If an image line is too close to the program line in the signal sideband, a small local oscillator shift will usually cure the problem (the frequency axes run oppositely for the upper and lower sidebands). One can also make small adjustments in the I.F. to change the placement of lines from the two sidebands. This option is discussed in detail in Section 7.7. Sometimes, lines from the image sideband can be used to advantage for calibrations or system checks. The sideband choices are labeled by codes which determine both the main sideband and the phase lock sideband. The choice of the phase lock sideband is strictly an equipment parameter that does not affect the sky frequency. Most of the Gunn oscillators in use at the 12 m require a certain lock sideband. The definitions of the sideband codes (SB) in terms of the resulting synthesizer frequencies are given below and in Chapter 3. = [(f,xy - 1.5 GHz)/M + 100 MHz)/N (7.1a) SB = 0 fºyn SB = 1 flyn = [(f,xy + 1.5 GHz)/M + 100 MHz)/N (7.1b) SB-2 f.y.-I(f,x, - 1.5 GHz)/M - 100 MHz/N (7.1c) SB = 3 flyn = [(f,xy + 1.5 GHz)/M - 100 MHz)/N (7.1d) In the equations above, fly, is the 2 GHz synthesizer frequency, frky is the sky syn frequency of the center of the signal band, M is the multiplier factor (harmonic) applied to the oscillator source to produce the LO frequency, and N is the harmonic of the 2 GHz synthesizer used to produce flyn. Note that 7-3 faky – f. * f(V) (7.2) and fo is the rest frequency of the observed line and f(V) is the velocity correction that compensates for the motion of the source. The computation of f(V) depends upon the condition of a control computer flag set by the parameters WNONREL and VREL. WNONREL is the default and causes f(V) to be calculated as f(V) - F. * (1 - V/c), (7.3) where c is the speed of light and V = Visa + VR, with Viss the radial velocity of the source relative to the Local Standard of Rest, and VR the projected velocity of the telescope relative to the LSR in the direction of the source. If WREL is in effect, then f(V) - F. (1 - V/c + 1/2 * V*/cº). (7.4) This latter expression is a second order expansion to the relativistic Doppler equation. 7.4 SPECTROMETERS Two spectrometer systems are available at the 12 m. The older, and still primary system at this writing, consists of analog filter banks. The newer spectrometer is a hybrid device, which is a combination of analog filter and autocorrelation spectrometers. The filter banks and the hybrid spectrometer were discussed in Chapter 3. 7.4.1 FILTER BANKS Most of the analog filter banks have 256 channels each. The filters are integrated, multiplexed, and recorded by the control computer every 100 milliseconds. A total of 512 channels can be recorded at a time, which means that two filter banks can be used for each scan. The filter spectrometers available and the ways 7–4 --------_s_* is s_*_* - wie ----_-_-_-_-_-_-_-_*.*.*.*.*.*.*.*.*.*.*--------.º.º.º.º.º.º.º.º.-----_-_-_-_-_-_-_* * * - e º 'º - - - - - - - - - - - - - - - e º is s_e + --------------------e. •ºeºeºsºte-tat-talataſe"sºa-a-a-a-a-a-aſ-Kºº-º-º-º-º-º-º-º-exº~~ -ºº e º Lº I* - & º-º-º-º-º-L-L-, -, -º º & © º e º 'º -\º ººº- - - - - tº º e Tºº a’s”sºe’sºsºsºsºsºsºs"sºº" "...","...”.”e"e"e”,”s”,”sºsºsºsºsºsºe"e"e". "a"e"e"e”,”, “eºs","e"s 7.4.2 HYBRID SPECTROMETER The hybrid spectrometer offers a number of bandwidth and resolution modes, listed in Table 7.2. (See also Chapter 3.) TABLE 7.2 Hybrid Spectrometer Modes No. of I.F.’s Bandwidth No. of Channels Channel Resl. (MHz) per I.F. (kHz) Multi-beam Mode: 8 300 192 1562 8 150 192 781 8 75 192 391 8 37.5 192 195 4 600 384 1562 One or Two Channel, Single Beam 2 600 768 781 2 300 768 391 2 150 768 195 2 75 768 98 2 37.5 768 49 1 37.5 1536 24 7.5 OBSERVING MODES Six primary spectral line observing modes are available: position switching (relative offset), absolute position switching, total power ONs and OFFs, automatic total power ON-OFF position switching, frequency switching, beam switching, total power grid mapping, automatic position switched mapping, and drift scan mapping. The attributes and applications of each is described in detail below. Signal processing and calibration for each mode is described in Section 7.6. 7.5.1 POSITION SWITCHING Position switching, called the PS mode, is the most common and reliable observing mode at the 12 m for general spectral line observations. It involves considerable overhead in telescope movement and requires that equal time be spent in the ON and OFF source positions, but the data quality is usually good. In this mode, the telescope moves between the ON position and a relative OFF position, which may be specified in either azimuth and elevation, or hour angle and declination offsets. Usually the offset is in azimuth, so that the ON and OFF positions are taken at about the same airmass. The best rejection of the atmosphere and the best spectral baselines are achieved with small angular switches. Choose the smallest switch possible, so long as you are confident that the OFF position is free of emission. PS data recorded on disk is a final spectrum formed from the ratio (ON-OFF)/OFF, where the ON and OFF data are total power samples. In contrast to the total power observing modes TPN and TPF, discussed below, the ON and OFF samples are not saved as separate scans for independent processing. Although the PS mode offers less flexibility in processing data than do the total power modes, it also reduces the total volume of data and makes processing easier. To reduce telescope movement and provide the best compensation for linear drif ts in atmospheric emission, choose the number of OFF-CN pairs to be a multiple 7-10 of 2. The observing cycle will then be repeats of an OFF-ON-ON-OFF pattern. Each ON or OFF is called a SAMPLE and each OFF-ON pair is called a REPEAT. The observer must tell the operator how long to integrate for each SAMPLE (the default is 30 seconds) and how many REPEATS per scan, or alternatively, the total length of the scan in minutes. A typical scan might be 6 minutes long, with 30 second SAMPLEs (meaning 6 REPEATS). You can, of course, vary the length of the scan to suit your own needs. Each ON-OFF pair can be edited individually with the LINE program (see Record Editing in the supplement to the LINE manual). The operator can issue the command to take scans one at a time, or can set the system into an automatic data-taking loop. Figure 7.2 shows an example of a spectrum produced by a PS Scan. The parameters of a PS scan that you must give to the operator are summarized as follows: O The relative offset position, which may be specified in either (Az, El) or (RA, DEC) coordinates. The maximum offset allowable is 2°48'. O The integration time for an individual sample (ON or OFF). 30 sec is the default. O The number of ON/OFF pairs (REPEATS) per scan (can be specified to the operator as the total length of the scan). • The number of scans to be performed for every calibration In easurement. 7-11 12. 1040 39 . O. . . . —26. O -91. O ... -- 156 . O | | | | 9. |_ - ººm- 6. – - - — 3 - || — —5. | | - | — 1 OO ... O —50. O O ... O 9% 60 . O 1 OO ... O • e”- Tsº IRC+ 1 O216 4 SCANS 3780–3783 TC-800 TS= 25.19 TIME= 14. O 31 Oct 1989 POS 09:45: 14. 8 13:30: 39-10 SYNTH, FREQ. REF: O9 : 45 : 14. 8 13 : 3O : 39 . . FREQ-339538.00 SYN=1 . 86995.734 VEL= -86. O DVºutºlºg, FB-1000...fij}:{}_. Otúrce Absolute position switching, called the APS mode, is useful when observing in complex emission regions where it is difficult to find an emission-free reference position. In such cases, position switching with (Az, El) offsets can be dangerous because rotation of the parallactic angle as the source is tracked across the sky may cause emission to rotate into the reference beam. You will want to search for an emission-free position as close to the source position as possible, and use this as the reference position. If you wish, you can compute the (RA,DEC) offsets to this position and use ordinary position switching. Most observers find it most convenient, particularly for future observations, to enter the absolute (RA,DEC) coordinates of the reference position and use the absolute position switching observing mode. - APS is identical to ordinary position switching except that the switching is done between two positions absolutely specified by their celestial coordinates. The reference (OFF) position should be given a different name from the signal (ON) position and is best placed in a different source catalog from the signal position. Data taking and calibration options are the same as for ordinary position switching. The parameters of an APS scan that you must give to the operator are summarized as follows. O The name of the source (ON) position and the number of the catalog which contains it; O The name of the reference (OFF) position and its catalog; O The integration time for each SAMPLE (ON or OFF). 30 sec is the default; • The number of REPEATS of an ON-OFF pair or the total integration time of the scan; * O The number of scans between each vane calibration, if that calibration method is chosen. 7.5.3 ToTAL Power ONS AND OFFs Two observing procedures, called TPN and TPF, are available for recording total power spectral line scans. The two procedures are identical, except that TPN tracks the ON (source) position and TPF tracks the OFF (reference) position. You must execute the procedures manually, one scan at a time. As such, these procedures are mainly used for diagnostic purposes. To use TPF and TPN, follow this prescription: 1) Provide the operator with the following setup information: e The source catalog and the source name (the ON position). • The (Az, El) pointing corrections and the reference offset position (OFF). The offset may be specified in AZ and EL or in RA and DEC. • ‘The integration time of the scan in seconds (the scan will have only one SAMPLE, i.e., REPEATS does not apply to TPN or TPF scans). 7-15 2) Have the operator perform a vane CALIBRATE, a TPF (the OFF scan), and a TPN (the ON scan) in that order. The scan numbers of the CALIBRATE and TPF will be stored in the header of the TPN scan for use in data processing. 3) To look at either the TPF or TPN Scans, type scan+ F for the first filter bank, or scan; S for the second filter bank. The displayed scan will be a total power bandpass. Unless the band contains a very strong spectral line, you will probably not be able to see any lines. To display a final spectrum, formed from the ratio (ON-OFF)/OFF * CAL, type - INSTALL TON (Loads a procedure from a disk file. You only need to load the procedure once per session on the analysis system.) scan:# TON for the first filter bank, or scan:#+1 TON for the second filter bank. The scan number should be that of the TPN (ON) scan. The TON procedure will use the last CALIBRATE and TPF scan to form the Spectrum. 7.5.4 FREQUENCY SWITCHING The frequency switching observing mode has two primary uses: to increase the on-source integration time through "in-band" switching and to alleviate the problem of finding an emission-free reference position when observing in a (spatially) complex emission region. It also entails less system overhead than most other 7-16 observing modes. In this mode, called an Fs observation, a reference spectrum is obtained by shifting the center frequency of the signal spectrum. In principle, this can be done by switching the frequency of the LO or an I.F. oscillator; at the 12 m, the former is generally used. If the frequency shift is small enough, the spectral line will appear in both the signal and reference spectra. When the resultant spectrum is formed, the line will appear twice, once in emission and once in absorption. The spectrum can be "folded" to obtain a V2 improvement in signal-to-noise. With this technique, which is called "in-band" or "overlapped" frequency switching, you are effectively observing on-source all the time. The primary drawback of frequency switching is that the spectral baselines are generally not as good (i.e., flat) as with position switching. This is because the two frequency positions each have their own spectral bandpass shapes which do not cancel in the computation of the final spectrum. If the lines are narrow and the frequency shift is small (say «10 MHz), acceptable results can often be obtained. One must also be careful of frequency switching in regions (spatial or frequency) containing many spectral lines in the bandpass. Frequency switching is effected by switching the phase lock loop offset frequency (the Lock IF) between two nearby settings, usually generated by separate oscillators. The oscillator settings must be set manually. The frequency of switching is usually 5 Hz and is generated by the spectral line multiplexer when so instructed by the computer. The phase lock circuitry must be able to lock at both the signal and reference frequencies. This places a practical limit on the magnitude of the shift of typically < 20 MHz. Some receiver systems use the fundamental frequency of the Gunn oscillator as the LO frequency. For these systems, a shift in the loop offset frequency will produce exactly the same shift in the Spectrum. other receiver systems, particularly the high frequency receivers, use a harmonic multiple of the oscillator source as the LO frequency. The desired frequency shift must be divided by the appropriate multiple before setting the loop offset frequencies. * You will usually want to know whether the reference frequency is higher or lower than the signal frequency, or in other words, where the apparent "absorption" and "emission" features appear in the band. This is dependent upon which sideband ("SB") is being used. Figure 3.15, which shows how the SB options are related in frequency space, and Table 7.3 will be of use in making this determination. Table. 7.3 Effect on Band Center Frequency of Changing the Lock I.F. SB Increasing the Lock I.F. will shift the band center to a frequency that is O lower l higher 2 higher 3 lower - To reduce "in-band" frequency switched data in the LINE data reduction system, use the parameters FS and FR and use the FOLD command. FS is frequency offset (in MHz) of the signal line relative to band center and FR is the frequency offset (in MHz) of the reference line. Fold is the verb which averages the signal and reference lines and displays the result. You should understand the workings of the oscillator system and calculate your own frequency settings (the "Friend of the Telescope" can help you with this). After doing so, the operator will set the oscillators for you. If possible, test the technique on a strong line before proceeding to a long integration on a weak line. Example 7.3 shows how to make the oscillator calculations for frequency switching. When performing frequency switched observations, you must decide upon the following parameters and give them to the operator: 1) The magnitude, sense, and symmetry of the frequency shift; 2) The switch rate (the usual setting is 5 Hz); 3) The total integration time of the scan. Frequency switched scans always consist of only one record and, hence, cannot be record-edited. §§§§§§gúštº - e - **-Keº e º sº e º ſºº-I-I-K-K-T-I-T-Ysſel is *Is sº, s-e----------I-I-I-I***Is Is & º e e s sº e º 'º - - - - - --_-_-_-_-_e_e_g s_s_º_e_-_-_-_-_-_-_- •.º. º.º. ----, - -_-_-_-_-_e_e_&_e_º_e e_-_-_-_-_- - - - e.e. a --------Tº-Taº ºrg" & "3" arº"º"-----------Yº" ºre"ºº" sº ºrg" ºrº" ------T-Y-T-Y-Tº-Teººg Is el eleTºT-T-T-I-T-T-I-T-Yº YºYº Iº e º ºr pºº-º-º-º-º-º-Ye"eTe Iglº IsIe ſeleTel - 7"-T-T-I-I-I-Ie IºIGIsIe Is I*I-I-I-I-T-T-I-I-I- **************eºsºe”s-sºsºsºsºs"sºe’s "sºº"e"e"e"e"s"sºe’s”sºsºsºsºsºe’sºaº"e"sºº"a"ºe"e"sºo"s"s"-"e"sºº"s"s"sºsMereºsºe’e”,”e's "e"e"e"e"sº*** ******s****.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*s erate e are starºte are ere evere are a twº eteratºre 7.5.5 BEAM SWITCHING Spectral line beam switching can be useful when observing small angular diameter sources and when the best possible baselines are needed. This observing mode involves the nutation (chopping) of the subreflector and a positional movement of the telescope and is thus called the BSP (beam switching plus position switching) mode. The technique is much the same as that used for continuum ON/OFF's. With the subreflector nutating at a rate of typically 1.25 Hz, the telescope is moved to place the source first in one of the beam positions and then in the other. The beam position which, for a positive source signal, produces a positive response in the spectrometer is called the "positive beam" and a sample taken in this position is called an "ON." Conversely, the beam position which produces a negative response in the spectrometer is called the "negative beam" and a sample taken there is an "OFF." A BSP scan always consists of four samples taken in the order OFF-ON-ON-OFF. The samples are taken in this order to get the best atmospheric rejection, the best baselines, and to reduce telescope movement. The integration time of one of the individual ON or OFF samples controls the total integration time of the scan (sample length times 4). The beam switching mode usually produces very good spectral baselines. The subreflector switch rate is such that atmospheric changes and filter bank anomalies are most often subtracted out. The primary restriction for beam switching is that the Source angular diameter must be smaller than the subreflector throw. The subreflector throw can be varied between 0 and 6 arc min. The default switching rate is 1.25 Hz. At this switching rate the observing efficiency is about 90% that of a position- switched scan, i.e., line intensities are about 0.9 that of a PS scan. This is because no blanking is applied during subreflector movements. Switch rates of 2.5 and 5.0 Hz are also available. The observing efficiencies are poorer at the faster rates but the cancellation of atmospheric drifts may be better. You must decide upon the following parameters in a beam switched observation and give them to the operator: 7-22 The subreflector throw. Changes in the throw must be made manually; the computer must be updated (manually) as to the new value of the throw. - can is the sample time x 4. The vane calibration method is available, although it is applied in a different manner than for position switched data (see below). 7.5.6 MAPPING The 12 m system offers four modes of spectral line mapping: mapping by manual offsets, automatic mapping of rectangular grids in either the total power or position-switched modes, and automatic absolute position- or frequency-switched mapping using catalog generation routines. In addition, the system offers an automatic spectral line five-point mapping routine, which is used most often for determining azimuth-elevation pointing corrections. Mapping with manual offsets is appropriate for small maps or maps with unevenly spaced points. For most rectangular grid mapping, we recommend the automatic position-switched total power mode. With the total power mode, you can choose to observe several ONs per OFF and thereby increase the observing efficiency. The other alternative for grid mapping is through automatic catalog generation. With this method, you build a catalog of positions and step through them, either automatically or through manual selection by the operator. This method works in either the automatic position switched (APM) mode or the frequency switched mode. 7.5.6.1 MANUAL OFFSETS Often an observer will want to make a simple source map consisting of only a few points. In such cases, manual offsets (in RA, DEC) from the center position are the easiest way to proceed. Follow these steps: 1) Enter the center position into a source catalog or tell the operator the name and position so that he can enter it manually; 2) Compute the offsets in angular units. For declination offsets, this is unambiguous. For right ascension, two cases exist: 7–24 a) You want true angular offsets in the RA direction, i.e., with the "cosine declination" correction made. Tell the operator the magnitude of the offset in minutes and seconds of arc and whether you want to go East (+RA) or West (-RA). Ask him to use the FORTH E/D (for East) or W/D (for West) offset command which makes the cosine declination correction; b) You want an RA offset in units of time. Convert the RA offset to arc measure by multiplying by 15. Tell the operator the magnitude of the offset in units of minutes and seconds of arc and whether to go East or West. Ask him to use the FORTH EE or WW commands which do not make an undesired cosine declination correction. 3) After each integration, loop to Step 2 and select a new point in the map. The header information on the spectrum displayed by the LINE data reduction program will show any offsets that have been entered. The offsets are given in (real) angular units. 7-25 iméâš - - - - - s - - - - 7.5.6.2 AUTOMATIC TOTAL POWER MAPPING OF RECTANGULAR GRIDS (TPM) With the total power mapping mode, called TPM, you can define a rectangular RA-DEC grid with different grid spacings in the RA and DEC coordinates. You can choose to observe several map positions (ONs) for each reference (OFF) position, and everal OFFs for each vane calibration scan. After defining the grid, you can choose to map a subset by specifying the beginning and ending row numbers, and the beginning and ending column numbers. The map is scanned row-wise, starting at the negative-most RA offset and the negative-most DEC offset. The TPM mapping procedure insists upon placing a map point on the center position of the map. This is regardless of whether there are an even number of rows or columns. To use the TPM procedure, proceed as follows: 1) Give the operator the following information (FORTH commands issued by the operator are in square brackets): b) d) f) g) h) The catalog and name of the source (map center position). Standard setup parameters, including the (Az, El) pointing offsets, the pointing tolerance, and the focus setting. The reference position offset (relative to the map center) in either the AZ-EL frame or the RA-DEC frame. The maximum RA-DEC offset is 2°48' from the source position. - The RA grid spacing in seconds of arc (real angle). [mm:ss XCELL] The DEC grid spacing in seconds of arc. [mm:ss YCELL] The number of rows (displaced in DEC) in the map. ISROwl The number of columns (displaced in RA) in the map. [SCLM] The integration time per ON or OFF (both must be the same) in seconds. [secºlo SEC !] - - - The number of map positions (ONs) to be observed for each reference position (OFF). [N/F] 7–27 --- * * * e_e & a s. sº º is is ºn e-º-º-º---------- *-*.*.*.*.*.*.*.*.*.*.*.*.*.*_* -e e_s e º a sie --_-_-_-_-_-_-_- *_º_*.*.*.*.*.*.*.*.*.*.e., s_º_*.*.*.*_-_-_-_--_-_-_-_-_- ----------------ºxº-º-º-º-º-º-º-º-º-,---------------------_*.*.*_*-* ºº: º-ºº: fºº: :*: sº - º & * Fºrz. - -T-Y- º: •,• ::::::::: :-º-º-º: §§§ 38; 5% &######$$5 §§ £ 3 º' ºº e-sºº rºs.ºrrºrs ºvºie vºve - • * * •=e_----rrºrs Trºs-rrºr ex-rºw rºe ſieje vºw-wºwie, bi-r-s-s-s-s 3:33& -I-I-Le a s Tºle Iº e g º eIº.º.º.I-I-L-_- *.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.e. sIsleſaleſe ºxalºeºeſs ºſey- e.e. ºw’sſaſs slºſeſt ºeſºeºsºe's elºw ſeſſeſ-º-º-º-º-Ye --_-_--_*_-_-_º_&_º_º_e_º.º.º.º.e.--_-I-I- ---------_-_-_-_-_-_-_-_e ********************************.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.* **************************************************** j) The number of OFFs for each vane CALIBRATE [F/C]. k) The beginning and ending rows of the map (optional) [BROW, EROW). 1) The beginning and ending columns of the map. (optional) [BCLM, ECLM] 2) When you are satisfied with the setup, the operator will start the map with the TPM command. 3) To display the spectrum of a single map point, type INSTALL TON (loads the procedure from disk) scan; TON for the first filter bank, or scan++1 TON for the second, where the scan numbers are those of the map positions (ONs). 4) To display a contour map of peak or integrated intensity versus position, consult the Spectral Line Data Reduction manual and auxiliary documentation. 7-28 º - - - • * - - - - - - e e a e - - e .*.*. - - - & •.”.” • - - - - - .*.*.*.*.*.*.*. - * * : * * * * •:---- - - : •*.*.*.*. * * * * * * - * * * * * ~ * *.*.*.*.*.*.* - The position-switched mapping routine PSM will generate a position-switched A-DEC grid map using relative offsets for its reference position. The reference offset can be specified in either the AZ-EL or RA-DEC frames. If you specify a Il RA-DEC reference offset, the map is equivalent to an absolute position-switched map since the reference position is always the same point on the sky. The map is done on a rectangular grid that can have different X and Y cell sizes. You can specify that only a subset of the originally specified grid be mapped. Each point of a PSM gri map is taken as a position switched scan using the PS observing algorithm, i.e., th telescope switches on and off source in the pattern OFF-ON-ON-OFF ...., where eac OFF-ON pair is called a REPEAT. You can also set the integration time of individual ON and OFF samples. XCELL the X (= RA) cell size in arc seconds; YCELL . . the Y (= DEC) cell size in arc seconds; SROW the number of rows to map; SCLM the number of columns to map: S/C the number of scans per vane calibrate; SEC the * of seconds of integration for each ON or OFF Sample: REPEATS the number of ON-OFF pairs per mapping point. When the map is executed, the RA step size in time measure is given by XCELL / [15 * cos (DEC) 1, i.e., the cosine declination correction is taken into account automatically so that all mapping grid offsets represent real angle on the sky. The following optional commands allow you to observe a subset of the grid specified by SROW and SCLM. The defaults for each parameter are given in parentheses. BROW the beginning row of the map (1); EROW the ending row of the map (SROW); BCLM the beginning column of map (1); ECLM the ending column of the map (SCLM). There is no hard rule to determine whether one should use PSM or TPM, the total power mapping mode. TPM is more efficient in the sense that you can use one OFF scan with several ONs. However, PSM may produce better baselines because of the switching pattern. As a general recommendation, we suggest that you use TPM for maps of strong lines and large mapping grids; use PSM if the lines are weak and baseline stability is critical. APM is also an alternative to PSM: it uses the same OFF- ON-ON-OFF... pattern but the mapping positions are taken from discrete catalog 7-31 entries rather than a grid built from offsets from a single central position. The PSM mapping procedure (like TPM) insists upon placing a mapping point on the center position of the map. fääi -_-_- *...*_e_e_º_-_-_-_-_-_-_-_-_*_*.*.*_*.*.*.*.*.*_*_-_-_-_-_-_-_*.*.*.* ****** *.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*. -. Tº Lº ºn... it ººz. - - - - -I-A-T re. Tº ſa Ie IsIe Tº - *. * - - *.*.*.*. *.*.*.*.* ." - * *.*.*.*.* **.*.*.* ..." •.-- - ** * - sºsºs º-º-º- - **** Jºº.º.º. -sz.º.•ºr.º.º.*…*.*.*.*.*.*.*º.” .*.*.*.*…* - -I-I-I-I-I-I-I-I-I-I- - - - - - sººsteºsteº.”.”.”e"º"e"sºsºsºsºsºsºsºsºs"sºº"e"s’s’s’s’s’s’s’s 7.5.6.4 AUTOMATIC MAPPING OF RECTANGULAR GRIDS BY CATALOG GENERATION (APM) - - The catalog generation mapping mode allows mapping of rectangular grids in either the absolute position switching mode (APM) or a frequency switching mode (FS-MAP). The grid can have different cell dimensions in the horizontal and vertical directions. The APM and FS-MAP modes execute by automatically loading one of the standard source catalogs (5 CAT) with the coordinates of each map point. Coordinates in either the 1950 Equatorial or Galactic frames can be generated. Although not strictly required, the map generation works best if the map center position and map reference position (for APM) are stored in different catalogs, neither of which is 5 CAT. To generate and then execute an automatic map, give the operator the following information: 1) The number of columns and rows of the grid. If n is the number of columns and m the number of rows, the operator will enter the information with the command (n-1)/2 (m-1)/2 MGRID 2) The grid step size in the horizontal and vertical directions. The units are always angular, but gridding in the right ascension or galactic latitude direction does not automatically correct for the cosine of the declination. If the cos(dec) correction is to be made, include it in the specification of the grid spacing. The operator enters the cell dimensions with the command mm:ss. mm:ss. MCELL 7–33 3) 4) 5) 6) 7) 8) -_-_-_-_-_-_-_*.*.*.* tºº Me: - *. & -º-º-º-º-T-Y-L-.e. •" state"s ******** •I-I-I- *::::: *a*s •,• -> - - - - - - - - - - - - - -I-I-I-I-I-I-º-º-º- s"sºa"e"e"e"e"e"e"s where the first angle is the horizontal spacing and the second is the vertical spacing. Whether the map is to be in the equatorial (RA, Dec) frame or the Galactic frame. The positions in 5 CAT will be in 1950 RA and DEC in either case. Whether the horizontal or vertical map coordinate should increment first. The default is horizontal. Whether the center position of the map should be reobserved every few map points and, if so, what the interval should be. The number of scans to take between each vane calibration, if that calibration mode is chosen. The names of the source center position and the reference positions and the catalogs that contain them. The standard observing parameters such as the integration time, number of OFF-ON repeats per scan, tracking tolerance, etc. When the operator has entered all this information, he will generate the map positions in 5 CAT. Only 34 positions will be calculated at a time. When these positions are finished, the next 34 positions can be generated without re-entry of parameters. In the normal mode, the operator will start the map at the first position and step through sequentially. He can skip about in the map upon request, however. In addition, he can also step through a catalog of mapping positions which you generate yourself. 7–34 : ***************** if Il - & * * * * * * * * s & 6 & 2 º' .*.*.*.*.*.*.*.*.*.*.*.*.* §fÉ : *. e 7.5.6.5 SPECTRAL LINE FIVE-POINTS Spectral line five-points are used most often to determine azimuth and elevation pointing corrections, but may sometimes be of use as a general spectral line mapping routine. The data are taken in either the position-switching mode or the beam- switching mode, and the map points are taken in the same order as in a continuum five-point, i.e., +EL, -EL, CENTER, -AZ, and +AZ. A listing of sources appropriate for spectral line pointing is given in Chapter 4, Table 4.2. To perform a spectral line five-point, the operator will need the following information: 1) Which source to observe. The source listing in Table 4.2 is by no means all-inclusive, but if another source is used, take care that it is really suitable for use as a pointing source. In particular, it should have an angular size that is smaller than, or at least comparable to the antenna beam size and possess an accurately known position; 2) The azimuth offset angle of the reference, to be used for position switching. 3) An initial guess for the azimuth and elevation pointing offsets; 4) The grid spacing "HP". As for a continuum 5-point, HP is usually chosen to be 1/2-FWHP. 5) The observing mode, position-switching (PS5) or beam-switching (BS5). 6) The integration time per point, as specified by the seconds per sample, and the number of REPEATS, consisting of an ON and an OFF sample for position-switching or an OFF-ON-ON-OFF pattern for beam 7-36 switching. The observer also must specify the integration time per sample (30 s is the default and is usually convenient). Table 4.2 gives suggestions for the integration times. The display of the map and the fit for pointing offsets is somewhat more involved than for a continuum five point. When in the POPS/LINE data reduction program, you must first install the reduction procedure from its disk file by typing INSTALL LF . Then type center seen number LF for the first filter bank, or center scan number 11 LF for the second filter bank. As explained in Section 7.4.1.1, a single filter bank may be split into two 128 channel halves, one for each polarization channel (PARALLEL mode), or the whole filter bank used for a single polarization channel (SERIES mode). After typing "center_scan number LF", you are asked some questions by the routine: "AVERAGE THE TWO RECEIVERS7 (1=YES, O=NO)" This question is asked only if the data were taken in SERIES mode. If the question is answered "yes," the routine averages the first and second filter bank to improve sensitivity. You should answer "yes" only if you are reducing the first filter bank; you will usually not need to reduce the two filter banks separately if averaging the two. 7-37 If the data were taken in PARALLEL mode, the two polarization channels in each filter bank are automatically averaged. The next question asked is "USE OLD BASELINE & INTEG. REGIONS7 (1=YES, O=NO)" The observer must define baseline fitting and spectral line integration regions for this routine. If these regions have already been accurately set, as, for example, in a five-point of the same source performed immediately prior to the present one, you can answer "yes" and speed up the reduction process considerably. If you answer"no," the spectrum at the center of the map is displayed on the screen, and the question "ENTER # OF BIL SEGS" is printed. This part of the LF routine is the same as the "BSET" procedure. The observer must enter the number of baseline segments to be used to fit a least-squares baseline. [NOTE: The order of the fit is determined by whatever NFIT is set to (the default is 1 -- see the LINE data reduction manual for a description of the baseline fitting facilities).] When the number of segments to be fit is entered, the graphics cross hairs appear and you must mark off the two ends of each segment with the cross hairs (move the cross hairs to the desired position and strike any key except RETURN, if using the MODGRAPH). When this operation is finished, the baseline is removed from the center spectrum and the spectrum is replotted. The prompt "ENTER INTEG. REGIONS" is printed and the cross hairs reappear. You should then mark off the two velocity/frequency extremities of the spectral line (or whatever region you wish to integrate over). When this is done, the question 7–38 "DISPLAY EACH SCAN7 (1=YES, 0=NO)" is printed. If you answer "no," the map and the fit for new offsets are printed out. If you answer "yes," each scan of the map, with baselines removed, is displayed on a single plot, one spectrum on top of the other. The final question asked is "TYPE 1 To contLNUE OR O TO STOP" If you approve of the fits, answer l and the map and fit for new offsets will be displayed. An example of the five-point map with explanatory annotations is given in Figure 6.6. 7.6 CALIBRATION. AND SIGNAL PROCESSING 7.6.1 vaNE AND CHOPPER wheel CALIBRATION The calibration mode used for almost all spectral line observations at the 12 m is the vane or chopper wheel method. In this method, a calibration signal is generated by differencing the signals recorded first on cold sky and then on an ambient temperature absorber. In 12 m vernacular, a vane is a paddle covered with microwave absorber that is switched in and out of the beam at a rate of about 1 Hz. A chopper wheel is, in this case, a chopping blade whose solid portions are covered with absorber and which rotates at a rate of typically 10 - 50 Hz. The calibration technique is identical with the two devices. The receivers currently in use at the 12 m are all equipped with vanes. - Chopper wheel calibration has been discussed extensively in the literature (see - Ulich and Haas, 1976 Ap. J. Suppl., 30,247, and Kutner and Ulich, 1981 Ap. J.,250, 341). The technique corrects for atmospheric attenuation and several telescope losses. At the 12 m, the temperatures resulting from this technique are on the TR’ Scale (Kutner and Ulich) which means that the temperatures are corrected for the 7-39 atmosphere and all telescope losses except for coupling of the source and beam. The beam is defined here to include the central diffraction lobe, all near-in sidelobes, and the error pattern (error pattern losses are often the largest of the uncorrected losses). Observers should be aware that other observatories using the chopper wheel method have different definitions of the basic temperature scale. Exercise care when comparing data! An essential part of the chopper wheel calibration method is the specification of the calibration scale temperature TC. To first order, TC is equal to the ambient temperature for a single sideband receiver. In actuality, TC is a function of mean atmospheric temperature, atmospheric optical depth, sideband gain factors, the rear spillover and blockage efficiency me and the forward spillover efficiency mas. For observations under typical atmospheric conditions, TG = 400 for single sideband operation and TC = 800 for double sideband operation for most 12 m receivers. TC varies with elevation, particularly for double sideband observations on the wings of an atmospheric line such as at 115 GHz. Recommendations for TC are available from the staff and a utility program exists on the VAX for its computation. The procedure for performing a VANE CALIBRATE is the following: a) set the calibration scale temperature TC. As explained above, TC is approximately 400 for SSB receivers and 800 for DSB receivers. The precise value of TC is dependent upon efficiency factors, temperature, atmospheric optical depth and elevation or airmass. Recommended values for TC can be provided by the 12 m staff. b) Perform a calibration cycle (called a CALIBRATE) at intervals which you prescribe. The interval should be small enough that the atmospheric transmission during the interval does not change appreciably. This depends on the atmospheric optical depth and its stability and the elevation. During stable conditions of low optical depth, a CALIBRATE every 10-15 minutes is usually sufficient. If the atmosphere is choppy 7-40 or the elevation is changing rapidly as when the source is rising or setting, more frequent CALIBRATEs may be necessary. The operator can command the system to perform a CALIBRATE before each position switched scan or before a specified block of scans. The length and number of repeats of a given CALIBRATE can also be specified. The default is 30 seconds, with the vane and sky sampled 15 times each at 1 second per sample. c) The result of a CALIBRATE is loaded into the GAINS array. To examine the GAINS, type G1 for the first filter bank and G2 for the second. Exact definitions of the signal processing are given in Section 7.6.3. During position and frequency switched observations taken in the AUTO mode, the telescope moves to the OFF position to take the CALIBRATE. 7.6.2 DIRECT CALIBRATION Note: The staff does not recommend this calibration procedure. We describe it here for completeness. In the direct calibration mode, called NO-CAL in the control system, the data are scaled by the system temperature and the atmospheric attenuation according to the relation TA - S R * - TS - exp(r. A), (7.5) where S is the signal array, R the reference array, TS the system temperature, re the zenith optical depth, and A the airmass. The exact expressions for NO-CAL signal processing are discussed below. The observer is responsible for the computation of TS and the measurement of re. The value for TS can include efficiency factors, or the 7–41 * ºf ... rºs"A." - rºº e.g. g. g., &3:35::::::::::::::3: *********** tº º ***** º ^sºsºsºsºe’sº ** g &_e * * * sº-º-º-º-º: > *. - sº e - e s sº a tº ºr 4 ººzºº ºf ºzº J. & Wºº & tº * *_º_e_e as e. e. g.º. 9 s tº ele. º. º.º. ****************** 3, e º sº *s antenna temperature can be scaled up in the data reduction and post-processing stage. One reasonable definition of TS is sº (1 + G / G)(TR. * Tºky) (7.6) 74 ſlfss - TS where Gi and G, are the image and signal sideband gains, TRx is the receiver noise temperature, T., is the antenna temperature of the sky, m, is the rear spillover efficiency, and mta, is the forward spillover efficiency. With this definition, the ge e sº e - - resulting antenna temperature is on the same scale (TR) as with the chopper wheel calibration. This calibration scheme has a certain appeal because it is direct and easy to understand. However, the method has several difficulties which prevent it, in general, from being as accurate as the chopper wheel method. First, in the absence of an automatic HOT/COLD/SKY load. system (which the 12 m doesn't have), you must make several time-consuming observations. These include tipping scans to measure the atmospheric optical depth, and manual HOT/COLD loads to measure the receiver noise temperature and possibly the sky temperature. If these measurements are not made frequently, receiver and atmospheric drifts may introduce calibration errors. In addition, measurement of an average atmospheric optical depth may not adequately correct for local cloudlets and other atmospheric anomalies. Finally, the chopper wheel method depends only weakly on me whereas the direct calibration method depends strongly on it. Although we do not recommend the NO-CAL method for most cases, you should follow this procedure if you choose to use it. a) Perform an ordinary WANE cal to look for bad channels in the filter banks and give the operator a list of the bad channels; 7-42 b) Tell the operator you will be using the NO-CAL method. He will first perform a dummy CALIBRATE to zero the bad channels. You will not need to perform any more calibrates. c) Tell the operator the value of Ts you wish to use. It's up to you to decide how to calculate this number, but you will probably want to measure the receiver noise temperature by a HOT/COLD load, in the least. d) Perform a tipping scan (this must be done in CONTINUUM mode – see Chapter 6). - e) Repeat steps c) and d) at intervals short enough to catch any significant system or atmospheric changes. 7.6.3 SIGNAL PROCESSING FOR POSITION AND FREQUENCY SWITCHED DATA - 7.6.3.1 VANE/CHOPPER CALIBRATES When a vane calibration is performed, a calibration array called the GAINS array is computed according to the formula c - at: . Tc, (7.7) Sci - Rei where Ci S- Cl is the effective system temperature for channel i, is the calibration signal (vane over the feed) for channel i, 7-43 Rei is the calibration reference (cold sky) for channel i, Zi is the zero value response of channel i with no input signal, and TC is the calibration scale temperature. The array of C. elements is called the GAINS array. The average effective system temperature of all channels in the multiplexer, is displayed and updated on the on-line status monitor each time a CALIBRATE is performed. Note that TS is an average of both receiver channels when a two-channel receiver is in use. The calibrated antenna temperatures (TR') that are recorded on disk are calculated by the formula S. - Ri Tº), - +-- * C. , (7.9) ( R). R; -e Z; × l where (TR'), is the calibrated antenna temperature for channel i, Si is the Source or ON signal, and R is the Reference or OFF signal. 7.6.3.2 NO-CAL SIGNAL PROCESSING In the NO-CAL mode, the antenna temperatures are calculated from the relation 7–44 S – R. (TA) - Z * TS + exp(ro-A), (7.10) i where re is the zenith optical depth (called TAU9 in the control system), and A is the airmass, calculated as 1/sin(elevation). All other symbols are defined in 7.6.3.1. 7.6.4 SIGNAL PROCESSING FOR BEAM switchED DATA Beam switched data are calibrated using the vane but the signal processing is different from position and frequency switching. When a calibrate is performed during a beam switching session, the GAINS array is defined as – R- ci Cl * TC , (7.11). where the terms are defined above. The antenna temperature scale is given by (rº - (s-R) - c. - (7.12) 7.7 CHANGING THE INTERMEDIATE FREQUENCY Occasionally an observing situation may arise in which a change in the Intermediate Frequency from the nominal 1.5 GHz is either necessary or desirable. One example of this is when the program line is just outside the tuning range of the local oscillator. Another example occurs when, for double sideband observations, it is advantageous to observe lines from both the signal and image sidebands for pointing, calibration, or simultaneous line search purposes and the image line is just outside the normal spectral bandpass. 7–45 These observing situations can be accommodated provided the I.F. needs to be changed by only a small amount. The I.F. system has a bandpass filter centered at 1500 MHz with a bandwidth of + 300 MHz. Any change of the I.F. must thus fit within the 600 MHz I.F. bandwidth, leaving room to include the filterbank bandwidth. Hence, the minimum I.F. can be 1200 MHz plus 1/2 the filterbank bandwidth and the maximum I.F. can be 1800 MHz less 1/2 the filterbank bandwidth. Lines in opposite sidebands can be separated by at most 3600 MHz less 1/2 the filterbank bandwidth, or in the least by 2400 MHz plus 1/2 the filterbank bandwidth. To adjust the I.F. bandwidth, the first I.F. synthesizer, which is normally set to 109.50000 MHz, must be changed. The equation for determining the synthesizer frequency is i- fif + 2442[MHz) - (7.13) ſayn 36 9 where fir is the desired I.F. If the lines are in opposite sidebands, fir - (fu - fº) / 2. (7.14) where fu is the upper sideband center frequency and f, is the lower sideband center frequency. This intermediate frequency must be entered into the control computer so that the local oscillator synthesizer frequency will be correctly calculated. Note that if the two target lines are at the center of their respective sidebands, they will fall on top of each other in the resultant spectrum. To keep this from happening, offset the line rest frequencies from the band center. If the signal sideband center frequency is offset by an amount 6, the signal and image sideband lines will be separated by 26 and will be symmetrically displaced about the center of the final spectrum. To observe with a non-standard I.F., follow this procedure: 7-46 b) c) d) f) Discuss your intentions with a staff member well in advance of the observations; Calculate the new synthesizer frequency according to the equations above. Make sure that you are not exceeding the 600 MHz bandwidth of the I.F. system. Ask the operator to dial the synthesizer frequency into the I.F. synthesizer that is nominally set to 109.5 MHz. Ask the operator to set the new I.F. into the control computer. If appropriate, offset the signal band center frequency from the line rest frequency to prevent overlap of signal and image lines. Remember to have the synthesizer set back to 109.50000 MHz when the special observations are finished. Step (f) above is especially important to remember as the computer does not check the I.F. synthesizer for a correct setting. If you (or the next observer) resume standard observations and the synthesizer is not reset to 109.5 MHz, the band center will be offset from what you intend. In addition, we highly recommend that you check you special observing configuration on a strong test line before conducting program observations on weak lines. 7-47 *…*..*…*…*..*.*.*.*.*.*.*.*.*…*…*…*.*.*.*.*.*.*.*.*..*..*..*..* • • • • • • • • • • • • • • • •· • • • • • • • • • • • • *...*..*..*.*.*.*.*.*.*.- - *...*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*..**...*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*..* .*.*.*.*.*…*…*..*..*..*..*..*…*.• • • • • • • • - - - - -• • • •• • • • • • • • • • - • • • • • • • • • • • • • • • • • • • • • • • • • • •_- - T-T-T-T-T-T- → • • • • • • • • • • • T • • • • • • • • • • • • • • • • • |-• ·• - ·- - - - - - - - - - -- - • • • • • *.º.º.º.º.º.º.º. • • • æ ø • • • • •*...*.*.*.*.*.*.*.*.*.*.*.*. • • • • • • • • • •--• • • • - - -• • • • |-----• • • • • •-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-- - - - - - - ·:·º·:·º·:·º·:·º·:·º·:·º·:·º·:·º·:·º·:·- - -- .*.*.*.*..* • • • • • • • • • - • • • • • • • • • • • • • .*.*.*.*.*.*.*.*.*..* � * • 4 • • -:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-: •* • *...*.*. • • • • • • • • • • • • • • • • • • • • •*. • • • • • • • • • • ► ► ► ► ► ► • ·:·º·:·º·:·º·:·º·:· •• • • • • • • • • • • • • • •• • • • • • • • • • • • • • ¶ • • • • • • • • • • •• • • • •• • • •• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • T • T • T •• • • • •• • • • • • • • • • • • • • • • • • • • T • T • T • • T • • • • • • • • • • • • • • • •• • • • •• → • • • • • • • •• • • •• • • • • • • • • • • • • • • • • • • • • • • • • • •• • • • • • • • •* ... • • •• • •-• • • • •• • • *º-º-º-º-º-º-º-º•• • • • • • • • • • • • • • • - - ae … • • • •- - - - … • • •• • • • • • • - - - - --- « œ • •- --• • • • • • • • • • • • • • • • • • • •- - - - -.• • • • • • • • • • → （- - - - - ... • 7 • • • • • • • • • • • • • • • • • • •- "- - - -----I • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •-T-T-T- → ↓ • • • • • • • • • • • • • • • • • • • T • • T • T • • • • • • • • • • • • • • • • • • • • • • • -T-T-T--• • • • • • • • • • • • • • • • • - • T • •• • • • • • •• • • • • • • • • • • • • • • • • • • • T • • • • • • • • • • • • • • • • • • • • • • • • • • • • • T • • • •• • • • • • • • • • • • • • • • • • -• • • • • •• • • • • • T - T -*...*..*• • • • • •*...*..*..*..*• • • • • • • • • ••• •• • • • ----• • • • • - - - - -• • • • • •* • • • • • • • • • • • • • • • •• • • • • • • • • • & & & & & & . & … （ …» *...*..*..*..*..*• •• T • • • • • T • T • T • T • T • • -* *T* * · · · · * .*.*.*.*.*.*.*.º.º.º.º.º.º.º.º.º.º.º.º.º.º.º.• • • • • • • • • • • • • • • • • • • • • •• º.º.º.º.º.º.º.º.º.º.º.º.º.º.º.º.º.º.º.º.º.º • - ， ， ， «» ， • • • • • • • • • • • • • • • • • • • • • • • * « · · · *� • •• • • • • •• • • • • • • • • • • • • • • • • • • • • • • • • • • • T • • • T • • • •& & & & • • • • • • • • • * • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • --------_-_e_s_s ,e_s_e_s_*.*_-_-_-_-_-_-_*.*.*_*_*.*.*.*.*.*.*_e_-_-_-_-_-_* * *_e, e.e. e., s_º - - - - --_-_-_-_e_e_e_*.*.*.*.*.*.*_-------------_*.*.*.*.*.*.*.*.*.*.*_-_--_-_-_-_*-*-e_s *********a*a*a*a**a*-Ca"e"sº-Talalataºtaº"efe’ssº-ºw"e"e"sºsº.º.º.ºsteºaºeºsºcºsº.” *** © <- & ** - - º *.*.* wº-yº" yºur e-e-rw-ye Twº-ev-rsivºy rºya vºw ºvºvºvers-ºf-y-º-º-º-ºryº-e-F-ºvº"Tera ºr e-rw-ſ e-º-ei vºw-v- w w w re-s_s_e - - - º-ºº-ººººººººººººººººººººººººººººººººº-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º-º- ere’s eaterestate-e-eeee-ere are eatereºsTere e ºsterstate"e"eteererºecºsºeteere evere"e"everetate’s e ere evere ere were eTººnTere e's sº ere’s evereterate everets 7.8 USING THE OFFSET OSCILLATOR The 12 m I.F. system allows you to displace the frequency of one I.F. (polarization) channel relative to the other. This capability allows neighboring lines that would normally be out of the spectral bandpass to be observed simultaneously. Such an observing configuration can be advantageous for certain detection projects and when you need good relative calibration of two or more lines. In terms of observing time, the use of the offset oscillator offers no clear advantage since the two frequencies appear in only one polarization each. One could achieve approximately the same signal-to-noise per unit integration time by observing a single frequency at a time and averaging the two polarizations, and then tuning to the other line and observing it in both polarizations. Furthermore, use of the offset oscillator adds a considerable measure of complexity to the observations, so you should budget adequate check-out time. The total separation of the main and offset sky frequencies must be within the I.F. bandpass of 600 MHz maximum for the same sideband, or 3600 MHz maximum for different sidebands. In addition, the mixer oscillators within the I.F. box must all be phase locked. For large offsets, the I.F. oscillators may not lock. The offset frequencies are entered by changing the frequency of the first mixer oscillator in the I.F. box. Each of the two I.F. channels can be set independently. The mixer oscillators are driven by synthesizers in the control room. The output of the synthesizers are multiplied by 36 to give a nominal frequency of 3942 MHz. Thus, the synthesizers are usually set to 109.5 MHz. Under the standard configuration, one synthesizer is used to drive both I.F. channels. When offset frequencies are requested, a second synthesizer is installed to drive the other channel. For this reason, you must give the staff advance notice if you want to offset the Second channel. 7-49 If the separation between the two frequencies is small (say «200 MHz), one of the observing frequencies can be entered into the control computer as the center frequency and the other frequency can be observed by offsetting one of the synthesizers. If the separation of the two frequencies is large, the center frequency entered into the computer should be midway between the two frequencies. The formula for computing the synthesizer frequency is in all cases 3942 : (f1 - f.) syn 36 MHz , (7.15) where fe is the center frequency entered into the control computer and f is the frequency of the center of the spectrum. The use of the offset oscillator can be tricky. Always set up a test observation on a known, strong line to check the operation of the system before starting the main observing program. Try to make the test setup as similar to the actual observing setup as possible (same sideband, etc.). Be sure to shift the frequencies of the synthesizers and local oscillator to see how the lines move in the band when frequency shifts are applied. Finally, remember that the synthesizers must be returned to 109.5 MHz before resuming normal observing. No safeguard exists against using the wrong synthesizer setting. In summary, follow this procedure when using the offset oscillators: a) Carefully consider whether the offset oscillators are really advantageous to your project. If you decide they are, give the 12 m staff notice well before your run begins. b) Decide where the lines should fall in the band and use Equation (7.15) to calculate the synthesizer settings. c) Give the synthesizer frequency to the operator who will set it in. 7–50 Test the setup, or one similar to it, before program observations of weak lines. . Set the synthesizers back to 109.50000 MHz when the special observing is completed. 7.9 KEY TO THE ON-LINE STATUS MONITOR The Spectral Line On-Line Status Monitor provides basic information about the status of the telescope and the observations that are underway. The observer should check the monitor frequently to see that the telescope and control system are configured as they should be. Figure 7.3 shows a sample monitor screen divided into several blocks. Definitions of the quantities in each block follows. Lines 1 and 2 SCAN SOURCE HORIZON LST - UTC DUT1 YEAR OBS OPR Line 3: Current scan number Source name Time to 15° elevation (rise or set) Current local sidereal time Current coordinated universal time UT1-UTC time correction (top) year, (bottom) date Observer's initials Operator's initials (Far right) Receiver identification code Lines 4 - 8. (Left side) CURRENT 1950. O ECLIPTIC OFFSET Apparent right ascension and declination of date RA and DEC at Equinox 1950 Source ecliptic coordinates RA and DEC offsets (RA in time units, DEC in angle units) 7–52 NGIGIHOS HOJLINOWN SQLVJLS ĢINIT "IVYHLOĢIAIS --cº LĢINHT|5)I.gſ Ț º $ z:= | I || ||±558łº º Ç Ģ Ģ º Ď,， º 3.5T Ģģ ţ Ņ"I køTI I Jk， 6 I Ģ Ģ Ī Ō.Ģ" (3$łºȚ§:ł{z \; {r £ º Ģ Ģ Ģ " (§T º £; £ĢT I GÌ| ſl d'HI 8I {ļļ I 1 CJ3I3 SHTA!!!38 · 5H93.3 3ſIÙ || ( ſ ) d 1 ( f )|d3 Sf1！} + TO 1/ I ſr$ 5Ų8{， E}{\{" Ț[3，3] º [ſ] | [] & -1 --i (Iºſi įg I {3！}(?!?...E5!?. E º TQQ5ȚT T!5- 85Ż №35 Ż: GI ĢZT ZZ: ‘ GT TĢ Ģ ĮȚZ.$5" BT --ğ º §Z.--Sd5 55? - QQ5Ż T :ł ſy I ſ', [] }} {{[] []3[?] -!5 , -! I Ū TI {{$3&lň∂XISTÊ THÍ ŤI:łHŌ Ō "IĘIHH JHJ MH£I ~ĢĒ Ī ŌzłH ZI ĢĞ] | []ĢĞ] | ? .|;|k}}{{{+Z£; £Ģ º QQ}{z ： " [35588 " ，Q" z G & T - Ț II ĢT | ©5T i Gj-1 H I [] d$)', $1J1Ø-1 {{!!}}-1 1814:Iſl H19 01 ĢT ; ÇſSiły i T1 BIS-|-|[]ĮŽĘ) I №.[3] º [}|]] | []Iasaeoſ * # @ : ğ Ģ Ī Ģj* T T | Ț ț¢ £ © –?|[|]?!?!?! Z850* 5ł,$3$}{z \; " ¡ ¿?.JIJ, Qęłº]{}{}, / * T Z: ; ÇIÇI | Z.5 ° § T | & |+ | € £ Z.TķJTI J. Jk/* Üſz i €38 i £ Ț 8 * # [ ] ſiły ſ 5غ (35ET 9 Ț (3 ł Ż .. 9E$ $ $ $ Ż.[I]{k}|}|}|[] []º 58 || E.T | & Ț ' [ ° {· Ž. I 24; † 5IHH?!?!(13 g }|[] I 1 k} (\ FIT EI H 1 || ||I2 kJ}|[] I l \j \{ IT []3[[Iº 19 º 8ț7 $IŠĶ|Ļ| Ūº & 1 &ł ſ T}}|-| {{!}} {}}|&| 8 QIQ XJR 100 ST 81 G-È È Ì {-ſ} ; &T Ț & i & T | Ț Ț§5 i §º’ſ ŽIŲ Į + ']?|I3383 Z &l:10 S80 58ĘTȚ ] [ [I31n1$"||| [] 2 I}{ [\ H HJÈ|[|[]|$}} kJJŠ I }|Ú (Right side) COMMAND ACTUAL Line 9 ERROR OFFSET Source azimuth and elevation (spherical coordinate conversion plus pointing corrections) Actual AZ/EL encoder readings Difference between COMMAND and ACTUAL Total AZ/EL offsets (sum of pointing offsets plus subreflector beam throw) (will contain mapping offsets when a map) Lines 10 - 11 ATM REFRT T(AMB) FO TC Tsys POINT +BEAM Number of airmasses (1/sin(EL)) at current elevation Refraction coefficient for elevation refraction pointing correction (") Ambient Temperature (Celsius) Radial focus zero position (in mm) The calibration scale factor used for VANE/CHOPPER cal The system temperature. In the VANE or CHOPPER mode, this number is an average over the multiplexer of the values in the GAINS array. In the NO-CAL mode, this is the value entered by the observer to scale the data. The Azimuth and Elevation pointing offsets, used to correct the telescope pointing model at a given sky position (MM:SS format) The beam offset, relative to the electrical axis, of the subreflector. For position-switched observations, the subreflector is locked in this position. 7-54 Line 12 HP Lines 13 - 16 F1 BW F2 BW F1 CHANNEL : F2 CHANNEL : CONFIG VEL VR/VLSR SB IF 'S FSO FREQUENCY Beam half-width at half-maximum (used as grid spacing for spectral line five-point maps) The resolution of the filters in the first filter bank. The resolution of the filters in the second filter bank. The multiplexer channels used by the first filter bank. The multiplexer channels used by the second filter bank. A code describing the filter bank mode in use. The key to the codes are: The center velocity of the source with respect to the Local Standard of Rest (LSR). The projected motion of the LSR in the source direction. The total velocity correction applied to the synthesizer setting is VEL + VR/VLSR. The sideband code (see Chapter 3 for definitions). Multiplier factor for the Local Oscillator Source The top number is the LOCK-IF (the phase lock loop offset frequency) and the bottom number is the first I.F. of the system. Frequency Switching Offset The top number in the input center frequency in GHz. The bottom number is the 2 GHz synthesizer setting calculated by the computer. The synthesizer setting is calculated from the LO equation and includes the velocity correction. 7-55 Lines 17 - 19 rol FOCUS SP(V) TP(V) MODE SCANS SAMPLES SEC TIME Pointing tolerance mm:ss (top - input, bottom - actual pointing error, sum of AZ and EL) - Actual radial focus at the current elevation (top input, bottom – actual) - Switched power voltage from analog backend (top - Ch. 1, bottom, Ch. 2) Total power voltage from analog backend (top — Ch. 1, bottom - Ch. 2) Observing mode (e.g., PS = Position-switching) Number of scans requested Number of continuum ON/OFF samples requested (top — total sample time requested; bottom - sample time remaining (top - total integration time requested for this scan; bottom - integration time remaining) 7-56 APPENDIX A PoſNTING EQUATIONS FOR THE 12 M TELESCOPE A.1 PRIMARY POINTING EQUATIONS The basic pointing model in use at the 12 m is much the same as that described by Ulich (1980 Int. J. Infrared & Millimeter Waves, 2, 293); much of this discussion is excerpted from that paper. The azimuth and elevation terms used to correct the nominal encoder positions are given by the equations AA - A, C.sec(E) - C'tan(E) + Itan(E)sin(A - A) + Ansec(E), (A-4) AE - E + B., cos(E) + Icos(A - A t) + Eth + R., f(E) (A.2) is the total azimuth encoder correction, is the azimuth of the source, is the azimuth encoder zero offset, is the collimation error of the electromagnetic axis, is the collimation error of the mount, is the tilt of the azimuth axis from the zenith, is the azimuth toward which the azimuth axis is tilted, is the observer-applied "thumb wheel" azimuth correction; is the total elevation encoder correction, is the elevation of the source, is the elevation encoder zero offset is the gravitational flexure correction at the horizon, is the observer-applied "thumb wheel" elevation correction, R is the weather dependent term in the atmospheric refraction correction (see below), - f(E) is the elevation dependency of atmospheric refraction correction (see below). The weather-dependent refraction coefficient, which is practically independent of wavelength, is given by R. - 21.36Pr/Tk - 1.66Pw/Tk 103030Pw/TÉ, (A.3) where Pr is the total surface barometric pressure (in Torr) Pw is the partial pressure of water vapor at the surface (in Torr), and TK is the surface ambient air temperature (in K). PT must be measured by a barometer at the telescope site. Pw may be calculated from the expression Pw - RH - e.at/100, -> (A.4) where RH is the surface relative humidity (in 96) and eat is the surface saturated water vapor pressure (Torr) and is given by As the 12 m does not have on-line digital weather instruments, Re is not calculated or updated during observations. Instead, a typical value for Ro, usually 52", is fixed as a constant in the pointing code in the control system. Under certain weather conditions, this assumption could produce pointing errors of up to 10" at low elevations. The elevation dependency of the refraction correction is given by | f | *. m cos(E) - A.6 f(E) sin(E) + 0.00175 tan(87.5° - E) (A.6) This term is recomputed for each elevation of observation. The 12 m staff determines the pointing coefficients on a 3- 6 month interval. Pointing sources are observed at as many azimuth and elevation positions as possible and the corrections necessary to receive peak flux from the source are measured. The corrections are then input to a fitting program and the coefficients are determined. The total rms of the fit is typically 3–5". A.2 SECONDARY POINTING CORRECTIONS In addition to the primary pointing corrections, a set of secondary pointing corrections are used at the 12 m. In azimuth, these corrections are given by the equation AA icos(E) - A1 cos(E) + C1, - (A.7) where the left-hand side of the equation corresponds to the "cross-elevation" azimuth correction on the sky, given at a particular elevation by the azimuth "thumbwheel" correction. In elevation, the secondary correction is AE1 - Bicos(E) + E1. - (A.8) These terms correspond to the linear (in cosine(E)) terms in the principal pointing equations given above: Ai is the supplemental azimuth encoder offset, C1 the supplemental electromagnetic collimation error correction, B1 is the supplemental gravitational bend error, and Ei the supplemental elevation encoder offset. Each of the four receiver bays have their own set of these secondary coefficients to compensate for slight differences between feed and mirror alignments in each bay. The intent of these pointing coefficients is to keep the required pointing offsets as close to zero as possible. The determination of these coefficients requires much less data than the main pointing equations and can thus be adjusted on a more frequent basis. VISITOR INFORMATION for the NRAO 12-Meter Millimeter-wave Telescope NATIONAL RADIO ASTRONOMY OBSERVATORY 949 N. Cherry Avenue Campus Building 65 Tucson, Arizona 85721-0655 Telephone: (602) 882–8250 May 1990 -_-_-_-_-_- eºs"sºeºsºeºeºeºsºsºeºs * -- - - I. OBSERVING OPPORTUNITIES AND RESPONSIBILITIES The NRAO 12-meter telescope is available, on a competitive basis, to all qualified scientists and students without regard to nationality or institutional affiliation. Financial support, in the form of travel funds and publication fees, is only provided to investigators employed by U.S. institutions. The procedure for submitting proposals to the NRAO and the mechanics of the evaluation and approval of these proposals are outlined below. Once scheduled on the telescope, the principal investigator has the responsibility for proper supervision of all aspects of the observing program. This means, for example, that each principal investigator is responsible for obtaining all calibrations and other receiver/telescope parameters necessary for the reduction of his/her data--the NRAO assumes no responsibility in these matters. For this reason it is the policy of the NRAO that the principal investigator, or one of his/her collaborators, be in residence throughout the observations to supervise the program. II. PROPOSALS FOR OBSERVATIONS Scientific proposals for use of the 12-meter telescope should be submitted to Director - National Radio Astronomy Observatory Edgemont Road Charlottesville, Virginia 22903–2475 The proposals, no more than 3 pages in length, should contain a thorough but succinct discussion of the scientific justification for the observations being proposed as well as a discussion of the sources to be observed, the manner in which the data will be taken, and an estimate of the telescope time needed to carry out the scientific program. A source list containing source identifications and coordinates should be included. For extensive lists (~50 objects), specific criteria defining the observing sample may be substituted. Special needs, instrumentation or software, should also be noted explicitly. A Cover Sheet on which this information can be summarized is appended; it should accompany each proposal. Once received, the proposals are sent to five referees--established scientists with broad backgrounds and considerable experience in millimeter-wave astronomy but unaffiliated with the NRAO--who consider each of the proposals individually and advise the telescope scheduling committee as to whether the scientific merit of the proposal is sufficient for them to be allocated time on the telescope and, if so, with what restrictions. Using the referees’ remarks as a guide, the observations are either scheduled or the proposal is returned to the proposer for further consideration or explanation. Proposals are reviewed, and the telescope is scheduled, in trimesters as follows: Proposals received by: 1 January 2nd trimester (1 April to 15 July) 1 July 3rd trimester (15 Sept to 31 Dec) 1 October 1st trimester (1 Jan to 31 March) Some time exists in each of the trimesters for proposals requesting frequencies lower than 270 GHz. Such proposals, if received before the deadline for a trimester, will either be scheduled in that trimester or, if unsuccessful, will again be considered in the subsequent trimester. A proposal unsuccessful in two consecutive trimesters will be dropped from the telescope queue and the proposer notified. Proposals for high frequencies (above -300 GHz) can be scheduled only in the first trimester (1 January to 31 March) for reasons of atmospheric transparency. The NRAO will take receipt of high frequency proposals at any time of the year and will referee the proposals upon receipt. Scheduling consideration will be deferred until the first trimester of the year. If a high frequency proposal cannot be scheduled on its first consideration, it will be dropped from the queue and the proposer notified. V-3 III. LOGISTICS OF OBSERVING AT THE 12-METER A. THE ARIZONA ORGANIZATION The following individuals should be contacted when questions arise in their areas of responsibility: Darrel Emerson Phil Jewell John Payne Pat Murphy/ Jeff Hagen Dennis Chase Jennifer Neighbours Bill Hale Nancy Clarke Site Director; responsible for general matters of operations policy. Handles detailed scheduling of the telescope; provides scientific assistance for users; handles telescope calibration and pointing. Responsible for telescope electronics. Real-time and analysis software. Responsible for the telescope and all operations on the mountain. - Responsible for 12-meter data archives and handling of observer data tape requests. Arranges transportation to Kitt Peak; handles shipping and receiving. - Coordinates visitor travel in and out of Tucson as well as lodging in Tucson. In addition, more general questions or comments pertaining to Observatory-wide activities (scheduling procedures, scientific or instrumentation priorities, inter-site relations) or specific criticisms of, or suggestions for, the Arizona Operations may be addressed to the director of the NRAO located at the Charlottesville, Virginia office. B. TRAVEL To the NRAO Tucson Office - It is most convenient for the observer arriving at the Tucson Airport to take the airport limousine to the NRAO office. The limousine, called the "Arizona Stagecoach", departs from a stand located about 50m on the right as one exits the main terminal building on the lower level. The limousine driver will know where Steward Observatory is on the UA Campus and will also know where the Kitt Peak National Observatory (KPNO) building is. The NRAO is found on the 5th floor of the Steward Observatory building directly across Cherry Avenue from the National Optical Astronomy Observatory (NOAO) office and KPNO. To Kitt Peak – The 12-meter telescope on Kitt Peak is 55 miles from the NRAO Tucson office. Observers travel to and from the mountain with U.S. government GSA cars. The cars, one for each observing team, are available from Bill Hale at the Tucson office. The observer should contact Bill at least a week prior to his observations to arrange for the vehicle. A current driver’s license is required for those driving GSA cars. Federal regulations require that GSA vehicles are to be used for official business only. They must not be taken to local tourist attractions or local restaurants. Because we have only two vehicles for observing teams, you are requested to return the vehicle to the downtown office as soon as your scheduled observing run is completed. The principal investigator should coordinate the return of the vehicle with Bill Hale sometime during his/her observing TUIIl. C. HOUSING ON KITT PEAK The NRAO maintains 7 rooms in 2 dormitory trailers immediately adjacent to the telescope for observers' lodging. Each room is provided with clean linens and towels. The observer is requested to make up his/her own bed upon arrival and later to return used linen, towels, and wash cloths to the clothes hamper at the conclusion of his/her visit. In addition to bedrooms, each trailer has a living area with a color television, a desk, and a small kitchen v-5 for the observer's use. (Contact the telescope operator if you wish to use the stove in the trailer’s kitchen; the gas to the stove is usually shut off.) As at all NRAO facilities, spouses are welcome. The necessity for maintaining quiet in the vicinity of the dormitory trailers generally precludes children from using these facilities. Pets are not permitted in the trailers or on the mountain. D. MEALS Visitors using the 12-m telescope are welcome to use the cafeteria on the mountain operated by Kitt Peak National Observatory. Children, however, are not permitted to use the KPNO cafeteria. The cafeteria is located at the summit of Kitt Peak approximately 2 miles from the 12-m telescope; observers usually drive their GSA cars to and from the cafeteria. Meal hours are as follows: Breakfast 0600 - 0800 Lunch 1130 - 1300 Dinner 1700 - 1800 - (1630 - 1800 during winter months) Note: At all the above hours a cook is present in the cafeteria to take orders. There is also a small kitchen in the KPNO dining area, open 24-hours a day, from which observers may obtain cold cuts, cereals, soup, etc. Observers may order a "night lunch" to be left in the cafeteria refrigerator, by filling out a form (found in the kitchenette area) before 1300 each day. V-6 E. LAUNDRY. A free, self-service clothes washer and dryer are available for the observer's use in the recreation building on the summit. F. RECREATION AND LEISURE Adjacent to the KPNO cafeteria is a lounge with a color television, stereo, magazines and card tables. Pool tables, ping-pong tables, and shuffleboard are available for the observer's use at the recreation building. Candy bars, soft drinks, gum and cigarettes may be purchased either at the KPNO museum or in the recreation building. G. CHARGES FOR ROOM AND BOARD While observing on the 12-meter telescope all observers will be charged $30 per night. This charge will cover all meals (whether eaten or not), lodging, and mountain services. Of this $10 goes to the NRAO for lodging and $20 is allocated to KPNO for food and other services. No charge for meals will be made on the last day an observer is at the telescope if dinner is not eaten on the mountain. To facilitate accounting, a clipboard is provided at the entrance to the KPNO cafeteria. On the NRAO clipboard observers should sign for all meals when they are taken; the column for lodging also should be checked for each night's stay on the mountain. All payments for meals and lodging are made to the NRAO. (1) Payment may be made in cash, check, or credit card (VISA, MasterCard, Diner's Club or Carte Blanche) at the Cherry Avenue office between 0800 and 1530 Monday through Friday when you return the GSA car. (2) You may sign an imprinted credit card form which is available at the 12-meter and we will fill in the amount for meals, lodging, and tapes, and send you a copy along with an itemized invoice which is marked "Paid". (3) If you do not pay at the time of your visit, an invoice will be sent to you. Payment by check should be made promptly to the NRAO Fiscal Division in Socorro, New Mexico. Note: Observers from foreign countries and U.S. observers who will be away from their home institution for more than 30–60 days should make every effort to pay their bill at the Cherry Avenue office prior to departing. H. TELEPHONE Long distance service is available for personal telephone calls through AT&T. All long distance calls should be recorded on the clip pad (located near each phone) unless charges are reversed or charged to a calling card/3rd number. You will be billed for all personal calls. To make an AT&T call, dial 9-1-A/C + 7-digit number. I. LIBRARY A modest library with recent issues of principal astronomical journals and books is located in the KPNO administration building adjacent to the 1.3 m telescope on the mountain summit. IV. OBSERVING INSTRUMENTATION/SOFTWARE: Visitors who require special hardware or software configurations should consult us (Electronics: John Payne; Computer Software: Pat Murphy/Jeff Hagen) well in advance of their observations. PROPRIETY: Observers are scheduled on the telescope with the understanding that - they are to pursue only the program described in their observing request. Since we have many observers from various institutions working on related programs, we require that any observer wishing to change their program or to exchange time with other observers, do so only with the consent of the Site Director. OBSERVER COMMENTS: In an effort to improve our facilities and service, we request that observers completing their observations provide us with a brief summary of their experiences, remarks about any difficulties they encountered, or suggestions for improvements. These remarks are not normally kept confidential. USER MANUALS: Four User Manuals are available which describe in detail the telescope control, data acquisition and data reduction programs that are implemented at the 12-meter. 1. User’s Manual for the NRAO 12-m Telescope - Describes observing setup, Source catalog, etc. 2. Spectral Analysis System - Spectral line reduction program and procedures. 3. CONDAR: Continuum Data Analysis - Off-line reduction of continuum data: programs and procedures. 4. Continuum Mapping with the 12-m Telescope - Observing strategies and data analysis for beam-switched maps. Copies of these manuals can be found at the telescope and at the Tucson office. V-9 Phil Jewell is the NRAO "Friend of the 12-m Telescope." At any time prior to, during, or after the observations, specific questions should be referred to Phil. Since telescope time at the 12-meter is so much in demand, observers will want to observe as efficiently as possible. A discussion with Phil prior to the observations may enable one to optimize the observations and make the most effective use of the time scheduled. GETTING YOUR DATA ON TAPE. The raw data may be saved on a Forth binary tape that is available at the end of your observing run. The charge for each tape supplied to you by NRAO is $11.00. Analysis system (VAX) tapes require some time to make and cannot normally be produced on the mountain. They are made on the downtown computer after the observing run. More than one file can be written on a tape depending on the size and density requested. All export tapes will be FITS format unless otherwise requested. The tapes will be mailed to you, at a cost of $13.00 each. You will receive a credit or a refund if the tape is returned to NRAO. Please complete a Data Tape Request Form before leaving the telescope. V. PUBLICATION OF RESULTS PUBLICATION OBLIGATION: The results obtained by NRAO staff and visitors are expected to appear in publication. Observers are urged to analyze their data and to publish their results with minimum delay. The accumulation of masses of unpublished data may be a detrimental factor in future considerations of requests for observing time. ACKNOWLEDGMENT: Whenever a significant portion of research was done, or observational material taken, at the NRAO, we request that the author include the following footnote in the text where the Observatory is mentioned: The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation. - VI. NRAO TUCSON OFFICE VISITOR FACILITIES: Office space has been set aside specifically for the use of visitors in the NRAO downtown office; we encourage telescope users to spend time with us prior to or upon completion of their observations. visitors will have access to a VAX-11/750 Computer identical to that on the mountain for data reduction at a more considered pace. The downtown computer is equipped with a laser graphics printer so that one can produce publication quality spectra and maps. In addition, visitors have access to a modest library in the NRAO office as well as to the very extensive Steward Observatory library. INFORMATION SHARING: The Arizona NRAO staff is very interested in the scientific results of the research that they support. Feedback, positive or negative, is desirable because it helps assure that our efforts are consonant with your goals. To this end we would particularly appreciate it if you would summarize your work in a brief and very informal talk, a "brown-bag" lunchtime talk, while you are with us in Tucson. Let any of us know if you would be willing to give such a presentation. VII. NRAO REIMBURSEMENTS A. TRAVEL REIMBURSEMENT: The NRAO will partially reimburse travel to and from the 12-meter telescope under the following conditions: (1) A reimbursement request must be submitted within 30 days of the completion of travel. (2) The NRAO will reimburse the cost of actual round-trip fare (not to exceed the normal coach airfare) less a deductible. The deductible is $150 or 0.25* ($300+ air fare) whichever is greater. V-11 (3) Original ticket receipts must be submitted to the NRAO when reimbursement is claimed. (4) Only travel originating within the United States or Puerto Rico will be considered for reimbursement. (5) Reimbursement will be made only to supporting institutions and organizations - – not to an individual. This policy is limited to persons affiliated with U.S. institutions. Reimbursement will be provided for one round-trip per person. As a rule, the reimbursement can be provided to only one observer per observing program, although reimbursement can often be made to a second person. If a second person desires travel reimbursement, he/she should petition the Arizona Site Director; the decision will be based on need and the current budget status of the Observatory. The secretary can provide the observer with a travel authorization form which the observer should send, together with the original air ticket stub, to the NRAO Fiscal Division, Post Office Box 0, in Socorro, New Mexico 87801. Visitors should expect to pay for all lodging and meals connected with their visit -- the NRAO does not reimburse these charges. B. NRAO SUPPORT FOR PAGE CHARGES: Users of the NRAO telescopes and facilities are encouraged to publish their scientific results in a timely manner. To this end the NRAO provides partial page charge support to scientists at U.S. educational institutions. When requested, the NRAO will pay the larger of the following: 1. One third (33%) of the page charges of papers reporting original observations made with NRAO instruments when at least one of the authors is eligible for Such Support. V-12 2. 100% of the page charges prorated by the fraction of authors who are NRAO staff members. (Further details can be found in the NRAO Newsletter of October 1988.) The specific procedure to be followed to obtain page charge support is: 1. At the time of submission, please send four publication copies of the paper to the NRAO Librarian, Charlottesville, Virginia, indicating the journal to which the paper has been submitted. One copy is for the Director's office; three copies are for the libraries. If you wish to have the preprint placed at the 12 m telescope, send one additional copy and indicate that it is for the telescope. The Observatory does not . desire to referee visitors’ publications prior to submittal. 2. At the time of acceptance for publication, please notify the Librarian in Charlottesville of the proposed date of publication and apportionment of page charges, so that the necessary purchase orders can be initiated. 3. All other scientific and administrative communications should be kept between the authors and the journals. V-13 Attached Figures: 1. Map of Tucson showing route from the airport to the NRAO downtown office. Map of southeast Arizona showing route from Tucson to Kitt Peak. Map of Kitt Peak showing mountain facilities. Map of 12-m site. The following forms are appended when the Visitor Guide is printed as a stand-alone document; these forms also appear in the Preface to the User’s Manual. Observing Application Cover Sheet Data Tape Request Form Observer’s Comment Sheet 5| GRAN'ſ RD Tº # NATIONAL RADIO A *: ASTRONOMY : OBSERVATORY NOAO : o —i SPE5DWAY N Blvd # 2 No 57 -N- S. © . -UNIVERSITY \l-l | 67H Sºf OF . . 3 #| g| ARIZONA congress w_\-*- Él BROADWAY < TUCSON, ARIZONA MILES O l 2 | | | | | | | | | [TTTTTTTTTTTTTT KILOMETERS TO KITT PEAK . *lo Wºº- | : TUCSON INTERNATIONAL AIRPORT ARIZONA C Görgloss §§ OFLORENCE BEN ". C - N - * - 4 f (35) --- | - ! | F-------- | ! | - | !. (j r - - - - * , * * * * AJOC ! {--- (---, | | - t- A4/24 GO //VD/A/V | A'5 SEA?!/47/OA/ : | ! - | ! -------> TUCSON] KITT PEAK Q9) **GS ÖSASABE º - º * - f º . - - VONOGALES SCALE IN MILES Aſaya// 4-Meter Je/escope KITT PEAK, ARIZONA - - ºf- 90" ſelescope f | ſ M 15 . . Je/escope (/niversity of Arizona $CA16 - \ \ * 3reward Observatory () \ 36" Je/escope - N - º | /2" ſe/escope º E | ~ | § | •j - NRAO as sº ...M., 12 in RAD 10 sº *visitor CENTER TELESCOPE ADMINISTRATION lºo" Jelescope BUILDING - & QUONSET HUI - (laundry) • AMcMath & Soſar Je/escope EMPLOYEES' AMcGraw -///// DINING HALL 32" ſelescoee e 36" Ie/escope 34 e 8 84" Je/escope m So/ar /6" Je/escope 36" Je/escope Vacuum Je/escope * Gaë wº $on - Já" Je/escope Alma NJ- - Jower C N |l[lO/\\/T ELISuz | N Ķ&ae ķ uuJOC] ,SJOqe ued % %% (X) Ķ Z # 191į el 1 EQUIPMENT AND CALIBRATION STATUS for the NRAO 12 m Telescope July 1990 Edited by P. R. Jewell I. INTRODUCTION - This report summarizes the current status of equipment and system calibration at the NRAO 12 m telescope. The following two sections give some general comments about equipment and calibration; the figure captions give detailed information about each of the graphs displayed. This report will be updated on a regular basis as the equipment and system calibration status changes. Before using the information contained in this report, check with the NRAO Tucson staff to see that you have the most recent version. II. RECEIVER STATUS The receivers available for general use at the 12 m are listed in Table 1, The NRAO 12 m Front-End Box Status Sheet. For each receiver, the table lists the frequency coverage, the amplifier type, a typical receiver noise temperature, the continuum sensitivity for each polarization channel, the bandwidth, the feed type, polarization of the feed(s), the calibration system, any remarks, and the engineer in charge of maintaining the receiver. Graphs of the receiver noise temperatures as a function of frequency are presented in Figures 1 - 5 for five receivers. Because the majority of observations done on the 12 m are of spectral lines, the noise temperatures are referred to the single sideband (SSB) scale. The 1.3 mm SIS receiver and all Schottky receivers are, in fact, double sideband (DSB) systems with no inherent sideband rejection. The noise temperatures are measured on the DSB scale. We assume, with some confidence, that the gains of the image and signal sidebands are equal and thus derive the SSB temperatures by doubling the DSB temperatures. The 90 – 115 GHz SIS receiver can be tuned to have a single sideband or double sideband response. Continuum observations are usually performed as DSB observations. Continuum sensitivity is often determined by low frequency excess noise rather than the noise temperature, however. Continuum sensitivities are listed in Table 1. Some of the noise temperatures were measured in the laboratory and some were measured on the telescope. The laboratory measurements were made through most or all of the receiver optics (in particular, the lens-corrected feed system and L.O. diplexer), and are representative of the values an observer will obtain with a hot/cold load measurement on the telescope. Measurements made on the telescope are made by holding hot and cold loads above the window to the receiver box. Note that the numbers plotted are receiver temperatures, not system temperatures. The effective system temperature is defined as r: - TR.[SSB] * (, Gi/G.)TAlsky] (1) sys ments,exp(-r) where Gi and G, are the image and signal sideband gains, respectively, TRx is the measured receiver temperature using broadband hot and cold loads, m, and miss are the rear and forward spillover efficiencies (see § III), and r is the atmospheric optical depth at the position of the observation. TAIsky] is the antenna temperature of the sky, defined as TAIskyl - niſm[1 - exp(-r) + (1 - m)Tem n,7,exp(-r). (2) In the equation above, Gi/G, is 1 for a double sideband tuning and 0 for a single sideband tuning, TM is the mean atmospheric temperature, Tapill is the spillover spil temperature, and Tbg is the cosmic background temperature. Additional information about the receivers is given in the Figure Captions. All 12 m coherent receivers use Gunn oscillators as local oscillator (L.O.) sources. Although most of the Gunns have broad tuning ranges, observing programs utilizing a wide range of frequencies may require more than one Gunn oscillator. We have included the coverage of the L.O. sources for the 3 mm, 1.2 mm, and 870 pm bands. S-3 Note that the 1.2 mm receivers (200 - 310 GHz) use a tripler and the 330 - 360 GHz receiver uses a quadrupler. A calibration curve for the throw of the nutating subreflector is also included. This curve will change if the control electronics are adjusted. The nutating subreflector is used for beam switched observations in both spectral line and continuum modes. This curve will be of use in varying the throw of the subreflector. The range of the throw is 0 - 6 arc minutes and is always switched in azimuth. III. CALIBRATION STATUS This section gives efficiency and calibration parameters for the 12 m telescope as they are presently understood. The aperture efficiencies and the corrected beam efficiencies have been measured at several standard frequencies. From these measurements, we have parameterized the telescope in terms of Ruze theory. All efficiency measurements were made at the Cassegrain focus and include the losses of the feed and all optics. The Ruze parameters thus include the net effect of the entire telescope and receiving system, not just the primary reflector. Several of the graphs are not based on direct measurement but are inferred from Ruze theory. These curves are identified in the figure captions. These calibration factors are intended for "first order" calibration of 12 m data and as an indication of system sensitivity in assessing the feasibility of observing programs. Observers requiring precise calibration should make calibration measurements at their specific observing frequencies. The NRAO staff will be glad to assist in these measurements. The calibration parameters of the telescope are listed in the following table. S-4 12 M TELESCOPE PARAMETERS Dish diameter D | 12.0 m RMS surface accuracy Oſ 77–85 pum Infinite wavelength aperture efficiency mAo 0.52 Surface deviation correlation size Co. 28 cm Feed taper function K. 1.22 Forward Spillover Efficiency Tris 0.75 Rear spillover and blockage efficiency m, (70 – 310 GHz receivers). 0.85 (330-360 GHz receiver) 0.78 Note: A range of values are given for the RMS surface accuracy. The aperture efficiency is fit best by the larger RMS values while the beam efficiencies are fit best by the smaller RMS values. This is probably the result of the astigmatism associated with the primary reflector. The astigmatism tends to broaden the beam which will degrade the response to a point source more than for an extended source. The numbers given above are appropriate for the conventional hyperbolic subreflector. An error-correcting subreflector is sometimes in use which improves the efficiency of the antenna. Consult the staff for the latest numbers. A final figure included in this report shows how the 230 GHz gain of the telescope to a point source varies with elevation angle. For extended sources, the fall- off in gain may not be as sharp as for a point source. The measurements and the estimated best fit curve are plotted. Additional discussion of antenna calibration theory is given in Baars (1973, IEEE Trans. Ant. Prop., AP-21, 461), Kraus (1986, Radio Astronomy, Cygnus-Quasar Books), and Kutner and Ulich (1981, Ap. J., 250, 341). Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 FIGURE CAPTIONS The single sideband receiver noise temperatures for the 1.3 mm SIS receiver. As this receiver is new at this writing (July 1990), the noise temperature measurements were made in a laboratory test assembly. All other receivers were measured in the telescope receiver chassis and include all receiver optics. The SSB receiver noise temperatures for the 200 - 240 GHz mixers in the 1 mm receiver package. The 1 mm receiver box contains 4 dual polarization mixer sets (8 mixers in all) covering the range 200 - 360 GHz. The SSB receiver noise temperatures for the 240 – 270 GHz Schottky mixer pair of the 1 mm receiver package. The SSB receiver noise temperature for the 270 – 310 GHz Schottky mixer pair of the 1 mm receiver package. The SSB receiver noise temperature for the 330–360 GHz Schottky mixer pair of the 1 mm receiver package. The L.O. frequency range of the Gunn oscillators available for use with the 3 mm receivers. The I.F. of 1.5 GHz allows signal sideband observations to extend another 1.5 GHz on either end of the plotted bars. S-6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 The L.O. frequency range of the Gunn oscillators (and tripler) available for use with the 1.2 mm receivers (200 -270 GHz). The L.O. frequency range of the Gunn oscillators (and quadrupler) available for use with the 270 - 310 GHz and the 330 - 360 GHz. receivers. The calibration curve for the subreflector control dial as a function of measured beam throw on the sky. This curve is subject to change if the electronics are adjusted. The conventional aperture efficiency, defined by the relation na - naoexp(-6°), (3) where 6 - 4” . (4) * - X - Representative measurements of this quantity at several frequencies are plotted. The conventional main beam efficiency, defined by the relation ApQM - - (5) 7/M x_ 7A A2 9 where m - 1.13%. , t - (6) Figure 12 Figure 13 Figure 14 and Ap is the physical aperture (113 m”). mM was derived from the aperture efficiency and the theoretical FWHP beamwidth. The main diffraction beamwidth (FWHM). This curve is plotted from the standard relation, X &M - K - , 7) M – “B ( At high frequencies, the azimuth beamwidth is broadened beyond its theoretical width by the astigmatism of the primary reflector. - Janskys per Kelvin of TA. This conversion factor is appropriate for converting point source antenna temperatures (standard calibration) to flux densities. If the source is extended relative to the beam, a beam resolution factor must be applied. Do not use this conversion for spectral line data calibrated by chopper wheel or vane. This curve is plotted from the relation * - + #. (8) Janskys per Kelvin of TR". This quantity can be used to convert point source antenna temperatures measured on the vane or chopper wheel calibration scale, Th", to flux densities. Measurements of this quantity at three different frequencies are plotted on the graph. This factor is given by the relation S, -> 'le'lfss 2k. (9) Figure 15 Figure 16 F igure 17 The corrected beam efficiency. This quantity can be used to convert - a TR* temperature to a main beam brightness temperature, provided that the source is not extended beyond the main beam. The corrected beam efficiency is the fraction of forward power in the main diffraction beam relative to the total forward power in the main beam plus error beam. The quantity is given by the relation Aeº 44% (10) nM. - || + where AE and AM are the amplitudes of the error and main beams, respectively, and 0B and 9M are the FWHM of the error and main beams, respectively. The FWHM of the error beam. This quantity has been measured at only one frequency; the plotted curve should be used only as a rough indicator of the extent of the error beam. The theoretical relation on which the curve was generated is given by 9s - 2012)*/* + 9 (11) Cy where cº, is the correlation scale size of surface deviations. The amplitude of the error beam relative to the amplitude of the main beam. As with the width of the error beam, this quantity is based on a theoretical estimate rather than hard measurement; use the curve only as a rough indicator of the relative amplitudes of the main and S-9 Figure 18 error beams. The theoretical relation on which the curve was generated is given by A 2c - * - – - |:l (exp(3*) - 1), (12) AM 7Ao | D where all the parameters have been defined above. The variation of antenna gain with elevation angle at a wavelength of 1.3 mm. The data points and a fitted curve are plotted. This curve is valid only for point sources. S-10 TABLE 1 NRAO 12 M FRONT END Box STATUS July 1990 APPLICABLE | FREQUENCY AMPLIFIER RECEIVER CONTINUUM 3 dB FEED TYPE | POLARIZATION | CALIBRATION SWITCHING REMARKS PERSONCs) TELESCOPE (GHz) TYPE TEMPERATURE I SENSITIVITY || BANDWIDTH VALUE SYSTEM IN - (KELVIN) (JANSKY / SEC (MHz) 12 M 90-115 SIS 125 SSB 1.0 600 HORN-LENS | DUAL-LINEAR 6 K NUTATING HYBRID LAMB SUBREFLECTOR CRYOSTAT 12 M 200-250 SIS 150 SSB TO BE 600 HORN-LENS DUAL-LINEAR N/A NUTATING CLOSED-CYCLE LAMB MEASURED SUBREFLECTOR CRYOSTAT 12 M 200-240 COOLED 500 SSB 7.0 600 HORN-LENS | DUAL-LINEAR N/A NUTATING LAMB SCHOTTKY - - SUBREFLECTOR 12 M 220-240 COOLED 600 SSB NOT 600 HORN-LENs | DUAL-LINEAR N/A NUTATING 8-BEAM PAYNE SCHOTTKY MEASURED - SUBREFLECTOR RECEIVER 12 M 240-270 COOLED 900-1200 NOT 600 HORN-LENS DUAL - LINEAR N/A NUTATING LAMB - schottky SSB MEASURED - SUBREFLECTOR 12 M 270-305 COOLED 1100-1600 NOT . 600 HORN-LENS | DUAL - LINEAR N/A NUTATING LAMB - SCHOTTKY SSB MEASURED SUBREFLECTOR 12 M .330-360 COOLED 1800-2200 NOT 600 HORN-LENS DUAL - LINEAR N/A NUTATING LAMB SCHOTTKY SSB MEASURED SUBREFLECTOR 12 M 5 ROOM TEMP. 100 SSB N/A 100 HELIX CIRCULAR N/A NONE FOR VLBI PERFETTO HEMT USE 12 M 38 ROOM TEMP. 200 SSB N/A 50 kHz | HORN-LENS CIRCULAR N/A NONE HOLOGRAPHY PERFETTO HEMT RECEIVER 200 – 250 GHz SIS Receiver Noise Temperatures Yº I (NIIR F LO Frequency (GHz) O SP - ſ J t ſ J I º U U U U U ſ ITI º ſ { U U | U U U U I U U U U I. Mixer F7 tºº 3 L. Prelimingry...ligb. Megàurements. Cº- NO Ks - * o P I C H-------------------------------------4------------------------------------------------------------4-------------------- NO H. - o ſ | Lſ) H---------------------------------------------------------------------------------------------------------------------------------- CN H. I o ſ I C), CN H. c ſ I Lſ) H. * - o I —r I O - H--------------------------------------------------------------------------- * O T * Lſ) L ºx- O T º l_1 | | ſ | | | | | | | | | ſ | | | | | || | ſ ſ f ſ | | | 190 200 21 O 220 230 240 250 260 270 200 — 240 GHz Schottky Receiver Noise Temperatures gº E. Rolarizdition 1 (Mixeſ; 3) tºº A Rolarizqtion 2; (Mixeſ. 17) . - tºº. - Measured 1987 Sep. | . tº *::==-4- A I / N amº / N / ; cº / N ,” . * jº / N. ,” \ fººm A&- ->+4 \---- - \ tºº. * V \ gº tº gº tº gº tº - - - \ * - . rºl - _ſh–5 S. - - Hºspº - TA- - - -4 : 1_1_1_1 l_ſ_ſ_l l_ſ_ſ_l FIGURE 2 l—1–1–1 LO Frequency (GHz) 95 200 205 21 O 215 220 225 230 235 240 245 240 – 270 GHz Schottky Receiver Noise Temperatures O O & F * Polarization 2 (Mixer 61) – ^_* Med:#ured 1989 January (l) 5 of tº O C T – § & - 8– T • Q) º H o P I .# 3 H º O CN e- 2. I s F------|-sy– - • - O H. * § 3 F – Oz T * CD H------------------4-------------------------------------------------->---4---------~~---4------------------------------ I (/) }º I 00 o E - C E – SN E I 32O S25 330 335 340 345 350 355 360 LO Frequency (GHz #2H27 | #2H2O | | (SIS RX) — | #2H23. | | - | | #2H3O | | | | | | | | | | | | . . . . . . . . . . . . | | | | || º - Ll Ll Ll - d L.O. Frequency 70 75 80 85 90 95 100 105 110 1 15 120 (GHz) * * r * | L.O. FREQUENCY RANGE *:::::H 3mm RECEIVERS | 5 ſºlº SCALE STE DRAMNG NO. B \3MMGUNN Do no scale Drawing sºft FIGURE 6 [ ºſ[\[[15)I）{ Bºs|9NW\/?$O ETIVOS 1ON OC1 NNnĐWW1\| 8 ‘ON SJN WAY№13JĀS:JYOS §EAÏïĪīŪūūī B0N\/\} )\ONE|[TÖB}}-} ‘O’T 99/g ciſ\/. 31W0 STMA0}}&ſ? NOU YON/m03 30NGOS TYNOMIWN 3+{1 \nța ſºonvoo »pun “ona sausſwaen galvoossy ſº peloxº SNOU, YM380 ſosºțul • A801WAŁ S00 AÑONOMISY OKUYM TYNOMIWN # Sºnº Nºw Q30 SMOTIOVAJ (№3&S 3 SW83}{10 SSTUR， $30ŅYMgTO! ± ș SèJBX|WN \}|\/c} „ĻONE(\OB}} + H9||H SĄJBX|W ç x *baug uun9 = Kouanbºu-, "O'T }}|Wc] « F-> KONBnO3H3 MOT (ZH.9) ogz gaz zzz goz ºgz ogz 9.sz zsz gyz wyz oyz 9cz zcz ºzz zzz Ozz 9lz zuz goz voz ooz 961|---- „KONE|[\Ö3}} + ”O’TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTIȚIIIIIIIIIIIIIIIIIIIIIIII →·||ff Ogiſ||9 | | #| !|!| |ggſ }}||6Żlſ} „º1… I-| NÕły | #!(x8 03348) |61 i #| !||| |Z9|| #||6:71 #! {|||– |9G| ||U|99 | #| !| 1 |----OVH}}| || !ÇgH#| #140 (X3) 270 280 290 #207 (X3) H #139 (X3) H JOO 310 #168 (x4) Hi! 40 (X4) | T | #156 (X4) H | Hilº!—ſº- ! * LL | | | | | | d L}_l i Ll L.O. FREQUENCY 320 330 340 350 360 370 (GHz) IOLFRANCES UNAESS NATIONAL RADIO ASTRONOMY 00SERVATORY - TUCSON OPERATIONS FRACTIONS DEC ANGLES operated by A SSOCATED UNIVERSITES (NC, under controcł with THE NATONAL SCIENCE FOUNDATION * º L.O. FREQUENCY RANGE - g/gal 300/345 GHz RECEIVERS B | \SUBMGUNN Do Nor scALE DRAWNG |ssºr FIGURE 8 | (uȚUuoup) Mouu L uudeG |DļOL 0 &1 C1 A 1.v.ſ. （A / G’9 9 Gºg g gºy y Gº 2 GºŽ Z G‘ İ I G’0 0 I|×I |- +v^！– |-æ|×·•{ :-）---šēši įööſö päiſistēſ"） |-Jºsé+ [MÞYJHLțWWEG TV1@]] # vzŽG’O H= [OŅILLES TVIG] - ?|ſi ſl?|||{|-ı| –ſ!|ſ! • uoņDuq|DO MOu.ųL UuDºg uoņO3|gºuqnS G'Z (senſpa F) 5uſhes ſold Joloaſalans O G’O G | G 2 (ZHŌ) Kouenbºu- o'i gano IJ 002 OGØ OOZ OG 1 001 OG 0 T-T-T-T）TTJTT JT.TT， UT， U1-1--1--|J， UT， UT-T-T-T）, | "O zºo 2 "O V(t +7'O KoueſoņJE Đunquedv G'O 9°O ITTTI | || | I I IT I TITITIT I ITI IT I I / I T-I-T-I s e. | | º I I I I ? I 1 | | 1 || ! 1 1 || ſ ! 1 ſº I ! I 9'O g"O +7'O 2’O Z'O | "O 833.§:g§ 3 | i ITTTT TTTI TI I I TTTI TITITI I I ITT I I ITT 3 3 ſº I I ſº I i 1_1_1_1 1_1_1_1 W_1_1_1 1 ſ 1 | f | 1 OO || O6 O9 O/ 09 OG O-7 (oes oup) "e § g § 3. 3 3 O O2 OZ Ol i (ZHŌ) Kouanbºu-€ I SH?HT10IJ OOV OGç 002 OGz 00Z 091 001 OG 0 •_-'！！∞） [ ] l-- [zgro = 9Wu ） VI.ļo uļ^|3). Jedsºſsupp OOZ OG 1 001 OG ('1), X. Kr OSC OO2 2.".3. Janskys per Kelvin of Ts' (For Vane Cal.) Frequency (GHz) C) GO ſ J | U U U U T U U J U U I U U U U J U U U | U U U U U U U O = 85 pum / SP ~mao-F-0.52. T m, = 0.85 § Tliss...}: O.75 3 / *- / O o || O. (O º - - Sº I _T O CN CD | ſ | ſ | | | ſ ſ | | l ſ | | ſ | ſ | | ſº | | | ſ | | l ſ | O 50 100 150 200 250 300 350 FIGURE 14 400 s : 5 g Corrected Beam Efficiency T U I : N = 77; p.m : I mao = 0.52 : H- N - Tº...H.0.85 - º N "lfss ~ ().75 - mºs N I N - * - N - º Sº O 50 100 150 200 250 300 350 400 FIGURE 15 Frequency (GHz) E I - O §º ~g tºº. I || O sº O . A–– i—T - dº ow gº Oz gz Oz gº ol 0 (uſu oup) *e 3 i Ratio of Error Beam Amplitude to Main Beam Amplitude O CN U J U r U U U J U J U U U U U U J | J lſ | J I | U ſ J J U - nao H 0.52 D = 12.0 m - C = #28 cm - / Lſ) Q = 77 pum º * * * º C. - <& O / I-> <ſ N Lil <ſ O | | ſ ſ - | | | ! I | | | | | ſ ſ ſ | | | ſ ſº ſ | | | | | | || O 50 1 OO 150 200 250 300 350 - 400 Frequency (GHz) FIGURE 17 (seeu690) →|6uV uoņD^êIE8 [ GIÀIſl5)I）{ 08 04 09 09 0V 09 0Č 01.）, þæ， J-TVT， J， T.T-T-T-ſ.|TIT.•ön į，] © |-J OD þærNI ſae•\O- |-* \\ © ſae \,-~] CNI ，\，●© |- QNJ OO •NJ-I |- þ滫∞ kºsN∞ N ：© ， N|• (O I> į į L 2 - 1 ] L9||-||4}y_4.864 ſpędnȘpg|W（~~~~-i-•º| – - ZHOį O’6ZZ :Kouenbeș-● ■ | ZYÈC] :30-anđS] Đ^JnOuondaeĘ-uſboUuuu 9Cº | \ e-Inlpuedual puueluv pez||Dulo N +BEAM 4-6 -BEAM 4-6 %5FF 6-9 mA 1-4 7ts. 1-4 mM 1-4 mº 1-4 re 6-32 1 mm Schottky receiver 1–5 1 mm SIS receiver 1–5 12 m Scheduling Committee 1-15 200–250 GHz SIS receiver 3–9 200–360 GHz Schottky receiver 3–9 3 mm SIS receiver 1–5 8-beam receiver 1–5 90- 1.16 GHz SIS receiver 3–4 Absolute position switching 7–13 Analog backend 1–7, 3-32 Analysis computer 3–34 Antenna pointing 6-26 Aperture efficiency 6–9, 6–44, S-4 APM 7–33 + APS 7–13 Arizona Stagecoach V-5 Associated Universities, Inc. (AUI) 1–1 Asteroids 5–25 Atmospheric attenuation 6–32 Automatic catalog generation 7–24 Azimuth limits 4–2 Azimuth transitions 4-4 Bad filter channels 7-8 Beam switching 6–4 Blanking interval 3–34 BS5 7-36 BSP 7-22 Cafeteria V-6 Calibration factors S-4 Calibration scale temperature 6-9 Canceling systematic errors 6–18 Catalog generation mapping 7–33 Catparse 5-7 Catxmit 5-12 Central mirror 3-3 Chopper wheel calibration 7-39 Clothes washer and dryer V-7 Comet and satellite positions 5-24 Computers 1-8, 3–34 CONDAR 2-7 Continuum observation 6-1 Continuum sensitivity S-2 Continuum status monitor display 6–55 Control computer 3–34 Corrected beam efficiencies S-4 Cosine declination correction 7–25, 7-31 Data Tape Request Form V–10 DBGAUSS 4–9 - DBMAP 6–20 Deputy Director 1-1 DIFTIP 6–37 Digital backend 1–7 Digital backend (DBE) 3-33, 6-6 Direct calibration 6–43 Direct calibration mode 7–41 DON-OFF 6–15 Dormitory trailers V–5 Double sideband (DSB) mode 3-4, 7-2 Drift scans 6–24 DSF 6-9 Dual beam mode 6-5 Index-1 Dual-beam reconstruction algorithm 6-18 EDLIN 5-4 Effective system temperature 1-11, 7-43, S-3 Eight-beam rotator 3-16 Eight-beam, 1.3 mm Receiver 3-12 Equipment and system calibration S-2 Error-correcting subreflector S-5 Export tape 1–8, V-10 FO 6–30 Fast-moving sources 4-1 File transfer 5-5 Filter banks 1-6, 7–4 Filter spectrometers 3–29 FITS format V-10 FIVE-POINT 6-26 Flux density calibrators 6-54 Focal Ratio 1-2 FOCALIZE 4–24, 6–30 Focus 4–24 Focus-Translation Mount 3–3 FOLD command 7–18 FORTH 5-14 - Frequency switching 7–16 Friend of the 12-m Telescope V-10 - Front-End Box Status Sheet S-2 FS 7 — 17 Fs-MAP 7–33 FTM 6–39 FTSBR 6–39 Geocentric velocity 5–26 GPOINT 4-17 GSA cars V-5 Gunn oscillators 3–21, S-3 GZFL file 1-8 Harmonic check 3–25 Heating of the feed legs 1–23 - * * * * º *a*a*a*a*. ---- ºr tº . ~ * * - - âûâûg - - - - --- - - - - - **-*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.sºsºs" º-º-º-º-º-º-º: Hot/cold load calibration 6-45 HP 6-26 Hybrid Spectrometer 1–6, 3-12, 3–31, 7-9 Hyperbolic subreflector S-5 IBM PC 5–1 IF Processor Module 3-26 IF system 3–26 Intermediate frequency 1–5, 3–4, 3–25, 7–45 IRFL file 1-8 Kitt Peak National Observatory (KPNO) V-5 Leveler Module 3–26 LF 7-37 Library V-8 LINE 2-7 Liquid nitrogen 6-45 LO chain 3-21 Local oscillator 1-4, 3-4, 3-21 Lodging V-5 - Lower sideband (LSB) 3-4 Lunchtime talk V-1 1 Manual offsets 7-24 Mapping extended continuum sources 6- 18 Meals V-7 Moon 5-22 National Optical Astronomy - Observatory (NOAO) V-5 NO-CAL 7-41, 7-44 Noise diode 1–7, 6–44 Noise temperatures S-2 Noise tube calibration 6-9 North-South translation stage 4–25 Norton Editor (NE) 5-4 NT 6-9 - Nutating subreflector 6–4 Index-2 Observations in the 330–360 GHz band 1-15 Observing frequency 6–3 Offset oscillator 7-49 ON/OFF measurements 6-12 Optical depth of the atmosphere 6-9 Optics 1–3, 3–1 PAFL file 1-8 Page charge support V-12 Parallactic angle 3-17 Parallel mode 1-6, 7–5 Payments for meals and lodging V-7 PC subdirectory 5–2 PCWRITE 5–4 PDFL file 1-8 Personal telephone calls V-8 Phase lock sideband 7–3 PKFL file 1-8 Planetary positions 4–1, 5–19 Pointing Accuracy 1–2 Pointing checks 4-10 Pointing coefficients A-3 Pointing corrections 4-6 Pointing equations 4-6 Pointing history 4-17 Pointing model A-1 Pointing sources 4-10 Position Angle 3-18 Position switching 7-10 Position-switched mapping 7-30 Preventive maintenance 1-21 Principal investigator V-2 Proposal submission deadlines 1-14 Proposals 1-15 - PS mode 7–10 Ps; 7-36 PSM 7-30 Quasi-optical diplexer 3–9 R-J-E temperatures 6-32 Radiometer equation 1-12 Rear spillover 6–18 Receivers 1-4 Recommended brightness temperatures 6-53 Rectangular grid mapping 7–24 Referees 1-15, V-3 Reimbursement request V-1 1 Rms noise level 1-12 Ruze theory S-4 Safety rules 1–23 SBMAP 6–20 Schottky barrier diodes 3-4 Scientific proposals V-2 Secondary pointing corrections A-3 SEQUENCE 6-12 Series mode 1–6, 7–6 Sexagesimal coordinates 5–3 Sideband codes (SB) 7-3 Single beam observation 6-5 Single sideband (SSB) 3-4, 7-2 Site Director 1-1 Slew Rates 1-2 Source catalogs 5-1 Source list 2-1 Spectral baselines 7-22 Spectral line beam switching 7-22 Spectral line contamination 6–3 Spectral line five-points 7-36 Spectral line mapping 7-24 Spectral line observing modes 7-10 Spectral Line On-Line Status Monitor 7-52 Spectral line pointing sources 4-15 Spectrometers 1-6 Spectrum Expander 3–30, 7–6 SPSTACK 6-43 - SPTIP 6-32 Standard backend 3-33 Stationary sources 4–1 Steward Observatory V-5 Index-3 gšiggg e e - e - º 4. - * ******.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*.*•ºsºsºsºe’sº * * *I*_*T*I-I-T-Y-L- e Te *** *Tº Tº STIP 6-39 - - | Subreflector 3–1, 4–6, S-4 Subreflector switch rate 6–4 Subreflector throw 4-8 Summer shutdown 1-1. - Superconducting (SIS) junctions 3-4 Surface Accuracy 1–2 SWITCHED 6-9 Switching phases 6-6 Synthesizer frequency 3–23 System electronics 3-4 TAUO 6-9 TC 6–9, 7-40 Telescope focussing 6-30 Telescope scheduling 1-14 Topocentric frame 5–26 Total power mapping 7–26 Total power spectral line scans 7-15 TOTALPWR 6-9 TPF 7-15 TPM 7–26 TPN 7-15 TR" scale 7-39 Tracking errors 4-4 Transmitting a catalog to FORTH 5-12 T 1-12 sky Tucson Airport V-5 - Upper sideband (USB) 3–4 User Manuals V-9 Vane calibration 7–43 VAX disk subdirectory 2–6 vi 5-4 VTERM 5-5 VTRANS 5-5 WL 6-30 Index-4 |||||||||| -** **JºhałAA, ff } 6