[daip] Issue running CVEL for a non-Doppler tracked spectral line set

[Michael Rosenthal]

Good afternoon,

We're using AIPS to reduce a K-band spectral line dataset. We're concerned
about the discrepancies in the spectra we see when running SETJY and then
CVEL on our data.

After completing steps from the guide for spectral line and astrometry
through the entire geodetic block, and for the main data up until EDITR, we
ran SETJY with the appropriate rest frequency and optical-helio velocity
for the central pixel, and then ran CVEL. We then used CLCOR to apply
solutions from the DELZN outfile from the geodetic block, and FRING+CLCAL
to apply a global fringe fit of our phase calibrator (FRING had a failed
solution rate of 2.5%) to the data. Finally we ran a self-cal on three
channels which have a strong line (~200 mJy) using CALIB.

At this point we inspected the results in POSSM. I've attached spectra for
two baselines (FD-BR and FD-SC) corresponding to the following:

   - POSSM_CVEL_CL10 - No self-cal, applied to the CVEL data.
   - POSSM_NAR_CL10 - No self-cal, but applied to the non-CVEL UV data,
   with identical calibration as in POSSM_CVEL_CL10 (CL #10 was copied over
   from the CVEL data using TACOP).
   - POSSM_CVEL_CL11 - Including self-cal, applied to the CVEL data.

You can see that the spectra look significantly better in some baselines
for the non-CVEL data, despite having identical calibration applied. S/N
only becomes comparable when the CVEL data has a self-cal applied. Do you
have any idea why this is, and which data should we proceed with?

For context: CVEL returned an average shift of ~15 channels (~7 km/s). We
thought this was quite large, but our observations did not use Doppler
tracking, so we continued. We also had around half of CALIB solutions fail
when doing self-cal on the CVEL data with solint 1.

Best,
Michael

-- 
*Michael Rosenthal*

Research Assistant
Center for Astro, Particle, and Planetary Physics
New York University Abu Dhabi
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