[vlbatests] Proposed update to SC pointing model parameters

[Kirill Sokolovskii]

Dear everyone,

I propose to introduce changes to the pointing model parameters for SC on the next maintenance day.
The new parameters are derived by jointly fitting in ptanal 7mm+1cm+2cm single-dish offsets measured between 2026 June 20 and now. I've checked that the single-dish data are consistent with interferometric pointings, but the fit is based on single-dish data alone.
Attached is a ptanal plot comparing the the Az El offsets as a function of Az and El before and after fitting the model. My interpretation of the plot is that there is a clear improvement, but there is also some small-angular-scale structure that cannot be captured by the model. That structure may be related to rail highs data - something to be investigated further. One final caveat - before fitting the model I manually removed 2cm data in two narrow Az ranges: -52 to -49 deg and +50 to +52 deg. The offsets in these ranges somehow don't follow the the general trend. No manual editing was done for 1cm and 7mm data.

#################### ptanal.parm ####################
SC,,EWTILT,-1.07  # CHANGE FROM -.99
SC,,NSTILT,1.29  # CHANGE FROM 1.33
SC,,AZENCZERO,-.18  # CHANGE FROM .14
SC,,ELCENTERINGCOS,-.54  # (=SAG) CHANGE FROM -.95
SC,,TRKFLEXC,-.14  # CHANGE FROM .01
SC,,TRKFLEXS,-.03  # CHANGE FROM -.17
SC,,TRKQUADC,-.14  # CHANGE FROM -.11
SC,,TRKQUADS,.11  # CHANGE FROM -.08
SC,,AZCENTERINGCOS,-.10  # CHANGE FROM -.04
SC,,AZCENTERINGSIN,.25  # CHANGE FROM .10
SC,2cm   ,AZCOLIMATION,-4.62  # CHANGE FROM -4.69
SC,2cm   ,ELCOLIMATION,8.53  # CHANGE FROM 8.78
SC,1cm   ,AZCOLIMATION,-.15
SC,1cm   ,ELCOLIMATION,5.26
SC,7mm   ,AZCOLIMATION,-2.86
SC,7mm   ,ELCOLIMATION,9.02
##################################################

Best wishes,
Kirill
-------------- next part --------------
A non-text attachment was scrubbed...
Name: seljun-octsinglefit.plotSC.ps
Type: application/postscript
Size: 3531476 bytes
Desc: seljun-octsinglefit.plotSC.ps
URL: <http://listmgr.nrao.edu/pipermail/vlbatests/attachments/20261016/c6add432/attachment-0001.ps>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ptanal.parm
Type: application/octet-stream
Size: 609 bytes
Desc: ptanal.parm
URL: <http://listmgr.nrao.edu/pipermail/vlbatests/attachments/20261016/c6add432/attachment-0001.obj>