******************************************** Argus Observer Instructions 2019.09.20 David Frayer (dfrayer@nrao.edu) ===================================================================== Example Argus observing scripts are located at: /home/astro-util/projects/Argus/OBS Example Argus GBTIDL reduction scripts are located at: /home/astro-util/projects/Argus/PRO ========================================================================= Observing Procedure: o Startup astrid and relax heuristics for pointing and focus tab. o Go online with control in Astrid, and run the argus startup script (when given permission by operator). The argus startup script checks the instrument status, turns ON the instrument if it is currently OFF, and pre-configures the instrument for the default 90 GHz parameters. o At the start of the observing session, run an AutoOOF to optimize the surface, unless observing extended sources during the day [astrid command: AutoOOF(source)]. This procedure will correct the surface for the current thermal conditions and derive the initial pointing and focus corrections. For AutoOOF, it is recommended to use the brightest point source in the sky between 25–80 degree elevation. If the Ka-band receiver is available, run the AutoOOF at Ka-band instead of Argus for more accurate surface corrections. After the AutoOOF solutions are applied, run a point and focus with Argus to confirm the telescope collimation offsets after the application of the OOF solutions. o Run autopeak focus with Argus, where the pointing source is > 1.5 Jy within ∼30 deg of the target region; brighter sources are better than closer sources since the GBT pointing model is fairly accurate. Choose a frequency that is the approximate frequency of your science frequency. For best results, autopeak focus should be run every 30 - 50 minutes depending on conditions (point more often during the day and after sunrise and sunset). Avoid pointing in the ”key-hole” (el>80 deg). o If pointing is problematic with Argus, e.g., observations during the day, or in periods of marginal weather, or in cases where the pointing source is too weak, observers can point and focus in X-band and use these telescope corrections for their Argus observations. Pointing and focus using Argus requires special attention, and users should not blindly accept the default solutions provided by the software system. Users can enter solutions manually as needed as discussed in Section ??. o After configuration and balancing VEGAS for science observations, check the power levels in the system. The VEGAS levels should be ∼ −20 +/- 3dBm. The target power levels in the IF rack (for beams 9-16) are 1.5 Volts. The Yig LO power level going into the instrument should range from ∼ 0.2–0.6 Volts. The power coming out of the warm electronics of Argus should read about ∼ 1.0–1.2 for beams 1-8 and ∼ 0.6–0.7 for beams 9-16. o Users must run the argus vanecal procedure to calibrate the data (/users/astro-util/projects/Argus/OBS/argus vanecal) after each configuration and/or balance for observations that need to be calibrated. The vane calibration is stable over longer periods than is needed for pointing and focusing, so only one argus vanecal procedure is required for each set of VEGAS observations between the pointing and focus observations. o It is best to observe similar frequencies together in time since it can take a few minutes for the YIG system to adjust to large frequency jumps. If you need to switch by a large amount in frequency (e.g., 4-10+ GHz), configure and wait a couple of minutes before observing. If the YIG LO power is low after a large frequency shift, re-configure again. o Only beams 9-16 that go through the GBT IF Rack can be configured with the DCR. All 16 beams can be configured with VEGAS using the 8 dedicated optical fibers for Argus beams 1-8. o Beam-8 has very little sideband rejection and will show higher noise when using the LSB at high frequency (e.g., when the O 2 atmospheric line is in the USB). o The ”Auto” procedures will run vanecal observations be default. For pointings/focus scans that do not need to be calibrated, observers could use the calSeq=False keyword in your observing scripts, e.g., AutoPeak(source,frequency=90000.,calSeq=False). If your frequency is not set, the default frequency for the Auto procedures for Argus is 86000 MHz. o It is recommended to run AutoOOF without the calSeq=False flag since this will properly calibrate the data from both beams in fitting for the surface model. Also, the Astrid ObservationManage- ment Log will report the system temperatures on the sky from the initial vanecal scans. Run the Argus AutoOOF at the default 86 GHz frequency (for higher S/N and software is semi-hardcoded for this frequency; i.e., astrid command: AutoOFF(source)). o Beam 10 is the default signal beam and beam 11 is the default reference beam for pointing, focus, and OOF observations. o The instrument performance using VEGAS can be checked by running the vanecal.pro procedure within GBTIDL. Example Argus data reduction scripts are located at /users/astro-util/projects/Argus/PRO. o For absolute calibration carryout PEAK scans with the associated vanecal observations (e.g., AutoPeak(souce) after applying good surface, pointing, and focus corrections for a source of known flux density (e.g., ALMA source catalog (https://almascience.eso.org/sc/). The ALMA calibrator catalog can also be used to check the strength of your pointing/focus source. The calibration methods and performance of the telescope are presented in GBT Memo#302. o Check instrument performance by reducing the vanecal observations within gbtidl, e.g., GBTIDL -> vanecal,25,ifnum=3 (zenith) Opacity(88.627500,57730.253) = 0.1096 AtmTsys(88.627500,57730.253) = 29.3598 Tatm(88.627500,57730.253) = 263.8712 beam, Tsys*[K]: 1 103.80726 beam, Tsys*[K]: 2 100.54533 beam, Tsys*[K]: 3 127.23248 beam, Tsys*[K]: 4 120.26474 beam, Tsys*[K]: 5 107.24904 beam, Tsys*[K]: 6 99.043334 beam, Tsys*[K]: 7 102.49700 beam, Tsys*[K]: 8 97.231515 beam, Tsys*[K]: 9 109.22220 beam, Tsys*[K]: 10 97.850002 beam, Tsys*[K]: 11 104.95907 beam, Tsys*[K]: 12 140.16193 beam, Tsys*[K]: 13 103.56645 beam, Tsys*[K]: 14 101.36605 beam, Tsys*[K]: 15 112.89979 beam, Tsys*[K]: 16 95.859751 Tcal, Twarm, tatm: 268.88648 270.74999 263.871 Note the Tsys* is the effective Tsys which is applicable for Ta* and includes the atmospheric correction. In comparison to the "standard" GBT definition of Tsys: Tsys* = Tsys*exp(tau_o*Airmass)/eta_l, i.e., Tsys is lower than Tsys*. ========================= Argus Trouble-shooting: o Confirm that the CIF and LNA are both on. If off, then run the Argus startup script. o Make sure the vane is in the desired position (e.g., obs for looking at the sky). If the vane is “stalled” or in an unknown state, click the Vane Obs button to move the vane to the obs position. If the vane is not already in the obs position, a configuration will also command the vane to the obs position. o Confirm there is LO power from YIG after configuration. o The status of the instrument is checked before each scan, and the scan will be aborted if there is not enough YIG LO power, or for other major issues. If the YIG power is too low, or the WIF power levels are low, and/or if one or more of the beam Status colors are red, reconfigure. If one or more the beams are bad, observations with the remaining beams can continue, but one must have sufficient YIG LO power to carry out Argus observations. o If Argus is in a “fault” state after configuration and multiple attempts to collect data, then: (a) Turn manager off and back on again (under the Mangers tab at the top of the Argus CLEO window) and reconfigure. (b) If cycling the manager does not work, have the operator restart turtle and/or “grail” and reconfigure. (c) If neither of the above work, then contact the Argus support scientist. o If Argus communication errors occur (e.g., Netburner time out error), then the recent commands given to Argus may not have taken and you may need to re-configure and re-issue your observing script. Within the Argus CLEO window, run a “prepare” to collect the current state of the instrument. If the LNA/CIF are off under the Status Codes, run the Startup script and then reconfigure. o If Argus communication errors persists, then: (a) Turn manager off and back on again, run the start-up script, and reconfigure. (b) If cycling the manager does not work, have operator hit the Argus reset button within the “Reset Box”. (c) If neither of the above work, then contact the Argus support scientist. ==================================================== Argus Technical Documentation ==================================================== Mapping Argus Beams to VEGAS Banks and the GBT IF channels -------------------------------------------------- VEGAS VEGAS Argus CM IF-Rack Dedicated fibers Bank (J) Beam OD "Mike's channels" -------------------------------------------------- A1 1 9 1 1 - A2 2 11 5 3 - B1 3 10 2 2 - B2 4 12 6 4 - C1 5 1 3 - 1 C2 6 3 7 - 3 D1 7 2 4 - 2 D2 8 4 8 - 4 E1 9 13 9 5 - E2 10 15 13 7 - F1 11 14 10 6 - F2 12 16 14 8 - G1 13 5 11 - 5 G2 14 7 15 - 7 H1 15 6 12 - 6 H2 16 8 16 - 8 --------------------------------------------------- where CM=converter module, OD=optical driver All beams can be connected to VEGAS, but only beams 9-16 that use IF-Rack OD channels 1-8 can be connected to the DCR. ======================================== Argus Beam Positions on the Sky The Argus beams are separated by 30.4 arcsec in Az and El in a 4x4 grid. Beam Numbers 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 ^ El | Az --> Offsets in arcsec Name XelOffset ElOffset 1 -45.6 45.6 2 -15.2 45.6 3 15.2 45.6 4 45.6 45.6 5 -45.6 15.2 6 -15.2 15.2 7 15.2 15.2 8 45.6 15.2 9 -45.6 -15.2 10 -15.2 -15.2 11 15.2 -15.2 12 45.6 -15.2 13 -45.6 -45.6 14 -15.2 -45.6 15 15.2 -45.6 16 45.6 -45.6 C 0 0 Beam 10 is the default beam for pointing and focus. =============================