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  • Setting up a VLASS schedule block in the OPT


    Eventually, we hope to automate (as much as possible) the creation of scheduling blocks. This is the current approach, which requires a combination of a priori decisions, Amy’s code to create source and scan files, Lorant’s code to create an SB file, and manual intervention to upload the files to the OPT and manipulate to tweak the SB.

    What an SB should look like

    • SB length goal is 4 hours.

    • All scans should be divisible by 0.45s (the dump time); easy/nice way to ensure this is with scans that are divisible by 9 seconds.

    • Avoid elevations < 30d for the OTF scans (if possible), < 20d for calibrator scans, and > 80d for all scans.

    • An initial long slew with “X band dummy” resource to get close to on-source before the setup. Length: 6m32.85s

    • Setup scan to set attenuators. Length: 1m3s

    • Setup scan to set re-quantizers. Length: 30.15s

    • Flux/bandpass intent scan on flux calibrator. Length: 3m

    • Slew to gain calibrator; goal is on-source time of at least 30 seconds. Gain calibrator also serves as pol leakage calibrator.

    • OTF scan + gain calibrator loops:

      • A “ready” scan at start position of a scan; on-source time of > 0s but as short as possible.

      • OTF scans currently require 7s of extra time in order to settle, then start moving.

      • Return to phase calibrator after 15–20 minutes. Length: 90s (including slew time) should be sufficient

    Current Procedure

    A priori decisions for a tile (with known boundaries in RA/dec):

    • Determine the phase calibrator(s) for the tile. (I am currently doing this with an SCT cone search of the NRAO calibrator manual, looking for sources with P-code in both L and C band, and as close as possible to the tile center (within 15 degrees of the tile center if possible). –AEK)

    • Determine the flux calibrator for the tile based on location/proximity. Choose best, but in this order of preference:

      1. 1331+305=3C286 (suitable polarization angle calibrator)

      2. 0137+331=3C48 (suitable polarization angle calibrator)

      3. 0542+498=3C147 (NOT for polarization angle calibration; can be used for leakage WITH monitoring)

    • Guess at LST start range for the tile (I am currently doing this by examining the elevation pattern for the flux calibrator and the phase calibrator(s); this can also assist in making choice of flux calibrator. –AEK)

    • Determine whether phase calibrator is closer to the east or to the west edge of the tile. This will be the side to start from (parameter –rastart in OTF_scans_from_tile).

    • Use to create a source list and scan list from the tile boundaries (see below).

    • Manually add a header to the scans.txt file containing info for Lorant’s code: # <flux cal> [beg/end] <LST start range> <phase cals>. The choice of “beg” or “end” is to indicate whether the flux calibrator will be observed first or last in the SB. For the moment, we plan to consistently observe the flux calibrator first. (An example header: # 3C286 beg 16:00-19:00 J2007+4029)

    • Use the scans file as input into Lorant’s code to create a file that can be uploaded to the OPT.

    • Upload the sources.txt file to the SCT and change the “Unnamed_Catalog” in the SCT to the name of the tile.

    • Upload the .4opt file to the OPT.

    • Manually modify the SB in the OPT to finalize. This includes:

      • ensure that the wrap is correct based on relative location of flux cal and tile (use wrap diagram)

      • add slew time to first phase calibrator scan (if necessary)

      • ensure that the scans have appropriate elevation (use block checker)

      • change (bulk edit) the Ready scans to DUR with the appropriate duration (e.g., 27 or 36 seconds) such that they have a very short but non-zero on-source time, i.e. between 0 and 9 seconds (use block checker)

      • double-check that the polarization leakage calibrator has large enough range of parallactic angle— >30d for “bright” calibrators (>1Jy), >60d for fainter calibrators (<1Jy, >0.5Jy)

    • Submit!

    • (Can determine overhead by comparing total SB length to the “Total OTF time” reported in the scans.txt file)