Instructions for GBT20A-539: Investigating the Ionized Gas of Cygnus X (Loren Anderson, Matteo Luisi, Will Armentrout, Dana Balser, Tom Bania, Dylan Linville, Trey Wenger)

Note: Our observing strategy and these instructions are identical to those of GBT18B -014.

Observing (C-band)

1. Run scheduling blocks sb01, sb02, sb03, etc.; Run these scheduling blocks in order. If a scheduling block is aborted or stuck then please re-run it. Our source will sometimes (usually during sb02) pass through elevation > 85 deg., and since the GBT cannot track sources that are that close to the zenith, this may cause Astrid to display a warning or abort the scheduling block. In this case, please abort (if Astrid has not aborted automatically) and run the next scheduling block.

Quality Control

1. Check the pointing/focus results. If the pointing or focus scans are bad then just abort and re-run the scheduling block. If the pointing or focus scans continue to fail after two attempts, use previous pointing and focus corrections if available; otherwise zero out these corrections.

2. Check the VEGAS bandpass. We are tuned to 64 spectral windows at 2 polarizations. Make sure we have a reasonable bandpass in all spectra. Since Astrid may crash when set to display all spectra, the best way to check the bandpasses is by opening a web browser and going to https://vegasdisplay.gb.nrao.edu. For example, below is a screen shot of the Vegasdisplay (on the left) where all bandpasses look ok. If the bandpasses significantly deviate from the screenshot, please reset VEGAS and run the scheduling block again. Lately, the Vegasdisplay has been offline a number of times. If it is offline, please check a few spectral windows in Astrid.

3. Check the power levels. Go to Cleo --> Launch --> Backends --> VEGAS and select VEGAS Power Monitor --> All measpwr. Power levels should be around -21 dBFS for all banks, except for one polarization in bank H for which the power level should be around -26 dBFS. Short-term spikes in the power levels are usually due to RFI and are ok as long as the power level returns to its normal value after a few seconds (see right-hand side of screenshot below). *If the power levels deviate from the above values by more than ~5 dBFS for several minutes, please reset VEGAS and run the scheduling block again.

-- MatteoLuisi - 2020-05-16

  • igp_54d6d4e9261f3777da820a74df74e38d_VEGAS_power_spikes.png:
    igp 54d6d4e9261f3777da820a74df74e38d VEGAS power spikes.png
Topic revision: r3 - 2020-06-15, MatteoLuisi
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