National Radio Astronomy Observatory Memo ---------------------------------------------------------------------- Updated: 2006 January 18 To : Observers From : The AOC data analysts Subject: Schedule files for the VLBA and/or stations with VLBA control systems 1. INTRODUCTION You have received this memo because your VLBI program involves the VLBA and/or a station with a VLBA control system. Currently, the latter type of station includes the VLA, GBT, and Effelsberg. This memo summarizes station information and points you to resources for further information and advice. However, the main purpose of this memo is to describe how you should prepare the ASCII schedule files needed for your program. Relevant deadlines are also mentioned, as are how to use the vlbiobs account at the Array Operations Center (AOC) and how to monitor the VLBA's actions during your program. 2. STATION INFORMATION The table below summarizes some properties of the VLBA, VLA, GBT, and Effelsberg, emphasizing known differences that might influence your observing strategies. =================================================================== Property VLBA VLA GBT Effelsberg ------------------------ ---- ---------- -------- ---------- sched station name <1> VLA1 VLA27 GBT_VLBA EB_VLBA sched station code <2> y y gb eb Can do VLBA/MkIV modes? yes yes yes yes yes Can do MkV? yes no no yes yes Number of head positions 14 14 14 14 14 Can do readback tests? yes yes yes yes yes Hi density on thin tapes? yes yes yes yes yes Simultaneous dual pol'n? yes yes yes yes yes<3> Receiver agility? yes yes yes some<4> some<5> Recommend `manual' pcal'n? no yes yes <6> no<7> No. of tape drives 2 2 2 2 1 No. of double-sideband BBCs 8 8 8 8 8 Maximum no. of BB channels 16 16 16 16 16 Maximum BB channel BW [MHz] 16 16 16 16 16 Complete station information <8> <9> <9> <10> <11> List of VLBA stations with MkV only recording capability: VLBA_HN, VLBA_FD, VLBA_LA, VLBA_KP, VLBA_BR ------------------------------------------------------------------- Notes: <1> VLBA_SC, VLBA_HN, VLBA_NL, VLBA_FD, VLBA_LA, VLBA_PT, VLBA_KP, VLBA_OV, VLBA_BR, VLBA_MK <2> sc, hn, nl, fd, la, pt, kp, ov, br, mk <3> Except 13cm at Effelsberg is RCP only. <4> Receiver changes between frequencies above 1 GHz require 10-15 minutes. Receiver changes between a frequency above 1 GHz and a frequency below 1 GHz require 10-15 minutes. Receiver changes between frequencies below 1 GHz require much longer times. For details see <>. <5> For details see <>. <6> Recommended above 10 GHz but not needed below 10 GHz. <7> No pulse calibration below 2 GHz. Beware that the the phase of the pulse cal signal is not recovered after switching receivers in receiver-agile observations. <8> VLBA Observational Status Summary available at www.aoc.nrao.edu/vlba/html/vlbahome/observer.html Send inquiries to your AOC contact. <9> VLBI at the VLA available at www.aoc.nrao.edu/vla/vlbivla/vlbivla/vlbivla.html Send inquiries to your AOC contact. <10> VLBI at the GBT page www.gb.nrao.edu/~fghigo/gbtdoc/vlbinfo.html <11> Joint VLBA + EFFELSBERG observing page available at www.mpifr-bonn.mpg.de/EVN/VLBA-EB-instructions Send inquiries to Dave Graham (graham@mpifr-bonn.mpg.de) or Richard Porcas (porcas@mpifr-bonn.mpg.de). =================================================================== Automatic tape allocation has been implemented at the GBT, the VLA and each VLBA antenna, freeing you from the burden of tape management. Effelsberg has only 1 tape drive, so automatic tape allocation is not practical; for that station you *must* allow a tape change gap of 10-15 minutes and follow the tape management advice in The Sched User Manual (see section 5) concerning tape usage and postpass avoidance. The phased VLA has special calibration needs; you can ensure that these needs are met if you use the scheduling program sched (see section 5) to make your VLA schedule files. 3. STRATEGIES FOR USING THE VLBA CORRELATOR Any program destined for correlation in Socorro *must*: + Adhere to the Guidelines for VLBA Observations available at http://www.vlba.nrao.edu/astro/obsprep/ + Include at least two observations, each lasting 4 or more minutes, of a fringe finder source, and ensure that the fringe finder is up at all stations. Correlator output on such sources is closely examined by AOC staff to assess correlation quality. The data analysts will reject any schedule lacking a recommended fringe finder, unless you can convince your AOC contact that another source will suffice. See the section on `Fringe Finders' in the VLBA Observational Status Summary available at http://www.vlba.nrao.edu/astro/genuse/ + Provide program cover information regarding correlation parameters, source positions, and shipment of distribution tapes. This information must be supplied by setting parameters in the sched keyin file (see section 5). Source positions for correlation should be accurate to < 0.5 arcsec * (22 GHz / f), where f is the observing frequency in GHz; if possible, it is desired that positions be better than this by a factor of at least 3-5, to provide the best results. If your program will require multiple correlation passes, then you may be able to optimize your observing schedule to reduce the correlation load; consult your AOC contact for advice. If your program requires pulsar gating, then your pulsar must be observed with a sched calibrator code `G' (see section 5) and you must supply the data analysts with an output file from the Princeton program tempo. This output file, usually named polyco.dat, describes the pulsar phase behavior with time. The Pulsar Gate Observer's Guide available at http://www.aoc.nrao.edu/~jbenson/pulsar_gate.html provides more informaton. Direct inquiries about gating to John Benson at the AOC (phone +1-505-835-7399; e-mail jbenson@nrao.edu). 4. STRATEGIES FOR USING THE VLBA Every program should include occasional readback test gaps, so operations staff can be alerted to take corrective action should recording problems be discovered. Readback tests are done automatically during an appropriate gap in the schedule. A gap must last 2 or more minutes when writing to a single tape drive, and 4 or more minutes when writing simultaneously to both tape drives. Once the VLBA is fully converted to MkV recording, readbacks will become irrelevant. Every program should include observations of a few amplitude calibration check sources, for the reasons outlined in the section on amplitude calibration in the VLBA Observational Status Summary available at http://www.vlba.nrao.edu/astro/genuse/ That section lists popular check sources and points you to resources for selecting other amplitude check sources. If your program involves phase referencing, polarimetry, and/or spectral line, then recommended observing strategies are described in the appropriate sections in the VLBA Observational Status Summary, available at http://www.vlba.nrao.edu/astro/genuse/ 5. SCHEDULE FILE PREPARATION WITH sched The NRAO scheduling program sched should be used to make detailed schedule files for programs in VLBA and/or MkIV formats. Global projects will typically use VLBA formats at stations with VLBA formatters and MkIV formats at stations with MkIV formatters. (MkIII formats are rarely used these days; please consult your AOC contact for futher information and advice if you must use a MkIII format.) Program sched is available via anonymous FTP, as described in the section in The Sched User Manual on installing sched. This manual is available at http://www.aoc.nrao.edu/~cwalker/sched/sched/sched.html Ancillary files for sched, including sources, stations, and frequency catalogs, plus setup files, are distributed with the program. Because sched and its ancillary files are continually evolving, it is best to make schedules using the latest versions. If you have trouble with sched contact Craig Walker at the AOC (phone +1-505-835-7247; e-mail cwalker@nrao.edu). Although sched can be run interactively, we ask that you compose a sched keyin (.key) file containing program inputs. Many observers find it useful to consult the example keyin files distributed with sched. If special setup files are needed for your program, then ask your AOC contact to validate them and include them in the keyin file. If you will be observing at nonstandard frequencies then you may be able to improve amplitude calibration by putting at least one LOSUM near the standard frequency at which the VLBA gain is measured; these frequencies are listed in the frequencies table in the VLBA Observational Status Summary, available at http://www.vlba.nrao.edu/astro/genuse/ You should compose and run your keyin file at your home institution to be sure the output is as desired. Program sched will generate the following schedule files for the following telescopes: + VLBA: Schedule files to control each antenna/tape system. + VLA: An observe file for the VLA in addition to a VLBA tape control file for the VLA's recording system. + GBT: Schedule files to control each antenna/tape system. + Effelsberg: A VLBA tape control file for Effelsberg's recording system. Antenna and receiver control files are derived from this. If your program is to be dynamically scheduled, then you will be sent additional instructions. A sched keyin file is needed. That keyin file must be prepared in local sidereal time at PT by specifying `LST=VLBA_PT' and then e-mailed to the data analysts (see section 6.2). 6. Copying files to the vlbiobs account 6.1. FTP Use FTP to deposit all your schedule files, including the sched keyin file, via ftp.aoc.nrao.edu at the AOC and send e-mail to vlbiobs@nrao.edu to inform the data analysts of your deposit. If `mmmyy' is a code for the month and year of the beginning of your program (e.g., jan06) and `pppppp' is your program code (e.g., bw999x), then all files must be deposited to directory /home/vlbiobs/astronomy/mmmyy/pppppp. Files must have names in lower case. The example FTP session ftp ftp.aoc.nrao.edu Name: vlbiobs Password: ftp> cd astronomy/jan06/bw999x ftp> put bw999x.key ftp> quit deposits a sched key file. The data analysts will submit all relevant schedule files to VLBA and/or VLA operations. If you deposit revised files to the vlbiobs account, then it is your responsibility to alert the data analysts and all stations about the revisions. The vlbiobs password can be obtained from an active vlbiobs user, the data analysts (+1-505-835-7238; e-mail vlbiobs@nrao.edu), or the AOC contact assigned to your program. If you wish to avoid transatlantic or transpacific phone calls then you may contact Walter Alef at the Bonn correlator (+49-228-525220) or Anastasios Tzioumis at his ATNF office (+61-2-9372-4350). The password should *not* be transmitted in an e-mail message. An e-mail user name is given for the data analysts so you can contact them by either phone or e-mail if you experience trouble accessing the ftp site. If you need to deposit schedule files on the EVN file server vlbeer, then access that server as described in the PI instructions available at www.mpifr-bonn.mpg.de/EVN/EVNinstructions 6.2. E-mail Send your sched keyin file via e-mail to vlbiobs@nrao.edu. The data analysts will place this file to the appropriate directory, modify the file for local use, and then run it on the appropriate vlbiobs account subdirectory. If you e-mail a revised keyin file to vlbiobs, then it is your responsibility to alert all stations about the revisions. If your program is to be dynamically scheduled, then close to the time of your observations the schedule files will appear in the appropriate monthly directory (see section 6.1). 7. DEADLINES Your schedule files *must* be available on the vlbiobs account by the due date specified by the VLBA/VLA Scheduling Officer. 8. NRAO/NM ADDRESSES AND PHONE NUMBERS You can reach the AOC data analysts at: phone: +1-505-835-7235 +1-505-835-7238 +1-505-835-7239 +1-505-835-7359 e-mail: vlbiobs@nrao.edu paper mail: NRAO, P.O. Box O, Socorro, NM 87801, USA Although most of your communication should be with the data analysts, you can reach the VLBA array operator and the VLA operator at: VLBA array operator: VLA operator: switchboard: +1-505-835-7000 +1-505-835-7000 phone: +1-505-835-7250 or 7251 +1-505-835-7180 or 7181 e-mail: vlbaops@nrao.edu observe@nrao.edu paper mail: VLBA Operations VLA Operations NRAO, P.O. Box O NRAO, P.O. Box O Socorro, NM 87801, USA Socorro, NM 87801, USA