Jupiter: continuum polarization calibration 5.5.0

Data Import

Import the data into CASA. Task importuvfits() will read the original AIPS friendly UVFITS format and create a CASA native MS.

importuvfits(fitsfile='planets_6cm.fits', vis='jupiter6cm.demo.ms', antnamescheme='old')

Data Inspection and Editing

First, check the observation set up and print verbose summary of the observations to the CASA logger

listobs(vis='jupiter6cm.demo.ms')

The output of this task is fairly long, the abridged version is shown below since we may need some of this information for reference later on during our calibration.

##########################################
##### Begin Task: listobs            #####
   Observer: FLUX99     Project:   
Observation: VLA
Computing scan and subscan properties...
Data records: 2021424       Total elapsed time = 85136.5 seconds
   Observed from   15-Apr-1999/23:15:25.0   to   16-Apr-1999/22:54:21.6 (TAI)

[...]

Fields: 13
  ID   Code Name                RA               Decl           Epoch   SrcId      nRows
  0    A    0137+331            01:37:41.299500 +33.09.35.13400 J2000   0          72946
  1    T    0813+482            08:13:36.051800 +48.13.02.26200 J2000   1         227524
  2    A    0542+498            05:42:36.137900 +49.51.07.23400 J2000   2         227058
  3    T    0437+296            04:37:04.174700 +29.40.15.13600 J2000   3         113424
  4         VENUS               04:06:54.109428 +22.30.35.90609 J2000   4         121098
  5    A    0521+166            05:21:09.886000 +16.38.22.05200 J2000   5          81258
  6    T    1411+522            14:11:20.647700 +52.12.09.14100 J2000   6         243608
  7    A    1331+305            13:31:08.288100 +30.30.32.96000 J2000   7         307958
  8         MARS                14:21:41.365747 -12.21.49.45444 J2000   8         118570
  9         NGC7027             21:07:01.593000 +42.14.10.18600 J2000   9         136082
  10        NEPTUNE             20:26:01.136316 -18.54.54.21127 J2000   10        157736
  11        URANUS              21:15:42.828572 -16.35.05.59272 J2000   11         99412
  12        JUPITER             00:55:34.043951 +04.45.44.70633 J2000   12        114750

Spectral Windows:  (2 unique spectral windows and 1 unique polarization setups)
SpwID  Name   #Chans   Frame   Ch0(MHz)  ChanWid(kHz)  TotBW(kHz) CtrFreq(MHz)  Corrs          
  0      none       1   TOPO    4885.100     50000.000     50000.0   4885.1000   RR  RL  LR  LL
  1      none       1   TOPO    4835.100     50000.000     50000.0   4835.1000   RR  RL  LR  LL

Sources: 26
  ID   Name                SpwId RestFreq(MHz)  SysVel(km/s) 
  0    0137+331            0     0              0            
  0    0137+331            1     0              0            
  1    0813+482            0     0              0            
  1    0813+482            1     0              0            
  2    0542+498            0     0              0            
  2    0542+498            1     0              0            
  3    0437+296            0     0              0            
  3    0437+296            1     0              0            
  4    VENUS               0     0              0            
  4    VENUS               1     0              0            
  5    0521+166            0     0              0            
  5    0521+166            1     0              0            
  6    1411+522            0     0              0            
  6    1411+522            1     0              0            
  7    1331+305            0     0              0            
  7    1331+305            1     0              0            
  8    MARS                0     0              0            
  8    MARS                1     0              0            
  9    NGC7027             0     0              0            
  9    NGC7027             1     0              0            
  10   NEPTUNE             0     0              0            
  10   NEPTUNE             1     0              0            
  11   URANUS              0     0              0            
  11   URANUS              1     0              0            
  12   JUPITER             0     0              0            
  12   JUPITER             1     0              0            

Antennas 27
[....]

##### End Task: listobs              #####
##########################################

Check also the array configuration and pick a reference antenna. Here, we will use antenna '11' as a reference since it's located in the middle of the array.

plotants(vis='jupiter6cm.demo.ms', figfile='jupiter6cm.demo.ant.png')

Calibration

Set the Flux Scale

Set the absolute flux density scale, but only for Stokes I at the moment. Our primary (flux) calibrator here is 1331+305 (3C286). The default model for CASA 5.3+ is 'Perley-Butler 2017'.

setjy(vis='jupiter6cm.demo.ms', field='1331+305')

Initial gain calibration

At this stage the data have an overall flux density scaling determined, but full gain solutions aren't there yet. The relevant task is gaincal() (analogous to the AIPS task CALIB). Gaincal() will produce a separate table with solutions, and we will use appropriate extensions to keep track of what is what.

Firstly, generate an antenna zenith-angle dependent VLA gain curve calibration table

gencal(vis='jupiter6cm.demo.ms', caltable='jupiter6cm.demo.gc', caltype='gc')

Now, solve for antenna gains on 1331+305 and 0137+331, using the just generated gain curve table (.gc).

gaincal(vis='jupiter6cm.demo.ms', caltable='jupiter6cm.demo.G', field='1331+305,0137+331', spw='', gaintype='G', calmode='ap', solint='inf', combine='', refant='11', minsnr=3, gaintable=['jupiter6cm.demo.gc'], parang=False)

# And check the solutions
plotcal(caltable='jupiter6cm.demo.G', xaxis='time', yaxis='amp', subplot='333', iteration='antenna')

If all looks good, bootstrap the flux density scale of the flux calibrator onto the phase calibrators. AIPS called it GETJY, but CASA calls it fluxscale().

myFluxscale = fluxscale(vis='jupiter6cm.demo.ms', caltable='jupiter6cm.demo.G', fluxtable='jupiter6cm.demo.Gflx', reference='1331+305', transfer='0137+331', append=False, display=False)

The output is displayed in the logger as well as stored in the myFluxscale python dictionary.

 Beginning fluxscale--(MSSelection version)-------
 Found reference field(s): 1331+305
 Found transfer field(s):  0137+331
 Flux density for 0137+331 in SpW=0 (freq=4.8851e+09 Hz) is: 5.29882 +/- 0.00457512 (SNR = 1158.18, N = 54)
 Flux density for 0137+331 in SpW=1 (freq=4.8351e+09 Hz) is: 5.35056 +/- 0.00178254 (SNR = 3001.65, N = 54)
 Fitted spectrum for 0137+331 with fitorder=1: Flux density = 5.32463 +/- 0 (freq=4.86004 GHz) spidx=-0.944519 (degenerate)
 Storing result in jupiter6cm.demo.Gflx
 Writing solutions to table: jupiter6cm.demo.Gflx

When executing fluxscale(), the calibration table with the extension .G is modified and stored as a new table with the extension .Gflx. So far, solutions have been generated only for the calibrators, and have not yet been transferred to the target source(s).

Before proceeding, inspect the flux density calibration and save results to a file.

plotcal(caltable='jupiter6cm.demo.Gflx', xaxis='time', yaxis='amp', showgui=True, figfile='jupiter6cm.demo.Gflx.amp.png')

plotcal(caltable='jupiter6cm.demo.Gflx', xaxis='time', yaxis='phase', plotrange=[-1,-1,-200,200], showgui=True, figfile='jupiter6cm.demo.Gflx.phase.png')

Polarisation calibration

Set the polarisation model

Now, set the polarisation model for the polarised position-angle calibrator (here 1331+305=3C286 which is also our primary flux calibrator). For polarisation properties of your primary polarisation calibrator see VLA Polarimetry Guide.

i0=7.3109    # Stokes I value for spw 0 ch 0
f0=4.8851    # Frequency for spw0 ch0 (note that in our data the 'lower' spw is actually higher frequency)
alpha=log(i0/7.35974932)/log(4.8351/f0) # Values from our setjy() run on Stokes I earlier
c0=0.114     # Fractional polarisation 11.4% for 5GHz
d0=33*pi/180 # Polarisation angle 33deg in radians

myPolSetjy = setjy(vis='jupiter6cm.demo.ms', field='1331+305', standard='manual', spw='0', fluxdensity=[i0,0,0,0], spix=[alpha,0], reffreq=str(f0)+'GHz', polindex=[c0,0], polangle=[d0,0], scalebychan=True, usescratch=False)

The results are displayed in the CASA logger as well as myPolSetjy python dictionary

#In CASA
CASA <49>: myPolSetjy
Out[49]: 
{'7': {'0': {'fluxd': array([ 7.26237491,  0.33674164,  0.7563341 ,  0.        ])},
  'fieldName': '1331+305'},
 'format': "{field Id: {spw Id: {fluxd: [I,Q,U,V] in Jy}, 'fieldName':field name }}"}

Solve for the leakage terms (D terms)

Solve for polarization leakage on 0137+331; assume it has unknown polarisation (poltype='D+QU' if good parallactic coverage, 'D' otherwise, consult polcal() help for more information on options).

Solve for the R-L polarisation angle (X-terms)

Template:Checked 5.3.0

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