Jupiter: continuum polarization calibration 6.4.1

DISCLAIMER

This is an advanced reference guide to calibration and imaging of pre-upgrade VLA polarimetric data with CASA 6.4.1. If you are a beginning or novice user, please consult relevant CASA guides first.

Data Import

This CASA guide discusses how to set the flux scale for calibration of an archival VLA 6cm data set (circa 1999), taken in D-configuration, with a resolution of around 14 arcsec. The original observation included several planets, among them was Jupiter, which will be the focus of this guide.

• The data set for this tutorial can be downloaded from this link: planets_6cm.fits (129MB).

CASA task importuvfits will read the original AIPS friendly UVFITS format and create a CASA native measurement set (MS).

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

Use listobs to check the observation setup 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 later on during our calibration.

##########################################
##### Begin Task: listobs            #####
   Observer: FLUX99     Project:   
Observation: VLA
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)

   ObservationID = 0         ArrayID = 0
  Date        Timerange (TAI)          Scan  FldId FieldName             nRows     SpwIds   Average Interval(s)    ScanIntent
  15-Apr-1999/23:15:25.0 - 23:16:11.7     1      0 0137+331                  8218  [0,1]  [3.3, 3.3] 
              23:38:38.4 - 23:48:01.7     2      1 0813+482                 87618  [0,1]  [3.3, 3.3] 
              23:53:38.3 - 23:55:21.7     3      2 0542+498                 19462  [0,1]  [3.3, 3.3] 
  16-Apr-1999/00:22:08.4 - 00:23:51.6     4      3 0437+296                 20728  [0,1]  [3.3, 3.3] 
              00:28:21.7 - 00:30:01.7     5      4 VENUS                    20560  [0,1]  [3.3, 3.3] 
              00:48:38.4 - 00:50:21.7     6      1 0813+482                 21016  [0,1]  [3.3, 3.3] 
              00:56:11.7 - 00:57:51.6     7      2 0542+498                 19914  [0,1]  [3.3, 3.3] 
              01:10:18.4 - 01:12:01.6     8      5 0521+166                 21248  [0,1]  [3.3, 3.3] 
              01:23:28.3 - 01:25:01.7     9      3 0437+296                 19604  [0,1]  [3.3, 3.3] 
              01:29:31.7 - 01:31:11.7    10      4 VENUS                    20634  [0,1]  [3.3, 3.3] 
              01:49:48.3 - 01:51:31.7    11      6 1411+522                 16446  [0,1]  [3.3, 3.3] 
              02:02:58.4 - 02:04:31.6    12      7 1331+305                 15366  [0,1]  [3.3, 3.3] 
              02:17:28.3 - 02:19:11.6    13      1 0813+482                 21136  [0,1]  [3.3, 3.3] 
              02:24:18.3 - 02:26:01.7    14      2 0542+498                 21248  [0,1]  [3.3, 3.3] 
              02:37:48.3 - 02:39:31.6    15      5 0521+166                 20196  [0,1]  [3.3, 3.3] 
              02:50:48.4 - 02:52:21.7    16      3 0437+296                 15456  [0,1]  [3.3, 3.3] 
              02:59:18.3 - 03:01:01.6    17      6 1411+522                 19474  [0,1]  [3.3, 3.3] 
              03:12:28.3 - 03:14:11.7    18      7 1331+305                 20398  [0,1]  [3.3, 3.3] 
              03:27:51.7 - 03:29:41.6    19      1 0813+482                 21124  [0,1]  [3.3, 3.3] 
              03:34:58.3 - 03:36:41.7    20      2 0542+498                 21660  [0,1]  [3.3, 3.3] 
              03:49:48.4 - 03:51:31.7    21      6 1411+522                 20316  [0,1]  [3.3, 3.3] 
              04:03:08.3 - 04:04:51.6    22      7 1331+305                 21118  [0,1]  [3.3, 3.3] 
              04:18:48.3 - 04:20:41.7    23      1 0813+482                 21360  [0,1]  [3.3, 3.3] 
              04:25:54.9 - 04:27:41.6    24      2 0542+498                 21680  [0,1]  [3.3, 3.3] 
              04:42:48.3 - 04:44:41.7    25      8 MARS                     15804  [0,1]  [3.3, 3.3] 
              04:56:48.4 - 04:58:31.7    26      6 1411+522                 20830  [0,1]  [3.3, 3.3] 
              05:24:01.7 - 05:33:41.6    27      7 1331+305                112178  [0,1]  [3.3, 3.3] 
              05:47:58.4 - 05:49:51.6    28      1 0813+482                 21040  [0,1]  [3.3, 3.3] 
              05:58:35.0 - 06:00:31.6    29      8 MARS                     20892  [0,1]  [3.3, 3.3] 
              06:13:18.4 - 06:15:01.6    30      6 1411+522                 20618  [0,1]  [3.3, 3.3] 
              06:27:38.3 - 06:29:21.7    31      7 1331+305                 20686  [0,1]  [3.3, 3.3] 
              06:44:11.7 - 06:46:01.6    32      1 0813+482                 18564  [0,1]  [3.3, 3.3] 
              06:55:05.0 - 06:57:01.6    33      8 MARS                     20744  [0,1]  [3.3, 3.3] 
              07:10:38.4 - 07:12:21.7    34      6 1411+522                 19950  [0,1]  [3.3, 3.3] 
              07:28:18.3 - 07:30:11.7    35      7 1331+305                 19460  [0,1]  [3.3, 3.3] 
              07:42:48.3 - 07:44:31.6    36      8 MARS                     21428  [0,1]  [3.3, 3.3] 
              07:58:41.6 - 08:00:41.6    37      6 1411+522                 22212  [0,1]  [3.3, 3.3] 
              08:13:28.4 - 08:15:21.6    38      7 1331+305                 22024  [0,1]  [3.3, 3.3] 
              08:27:51.7 - 08:29:31.6    39      8 MARS                     19500  [0,1]  [3.3, 3.3] 
              08:42:58.3 - 08:44:51.7    40      6 1411+522                 22158  [0,1]  [3.3, 3.3] 
              08:57:08.3 - 08:58:51.6    41      7 1331+305                 21470  [0,1]  [3.3, 3.3] 
              09:13:01.6 - 09:14:51.7    42      9 NGC7027                  16062  [0,1]  [3.3, 3.3] 
              09:26:58.3 - 09:28:41.6    43      6 1411+522                 19808  [0,1]  [3.3, 3.3] 
              09:40:31.7 - 09:42:11.6    44      7 1331+305                 19742  [0,1]  [3.3, 3.3] 
              09:56:18.3 - 09:58:11.7    45      9 NGC7027                  19458  [0,1]  [3.3, 3.3] 
              10:12:58.3 - 10:14:51.7    46      8 MARS                     20202  [0,1]  [3.3, 3.3] 
              10:27:08.3 - 10:28:51.6    47      6 1411+522                 20504  [0,1]  [3.3, 3.3] 
              10:40:28.4 - 10:42:01.6    48      7 1331+305                 19554  [0,1]  [3.3, 3.3] 
              10:56:08.4 - 10:57:51.7    49      9 NGC7027                  19912  [0,1]  [3.3, 3.3] 
              11:28:28.3 - 11:35:31.7    50     10 NEPTUNE                  87260  [0,1]  [3.3, 3.3] 
              11:48:18.3 - 11:50:11.7    51      6 1411+522                 21338  [0,1]  [3.3, 3.3] 
              12:01:35.1 - 12:03:11.7    52      7 1331+305                 15962  [0,1]  [3.3, 3.3] 
              12:35:31.6 - 12:37:41.6    53     11 URANUS                   21824  [0,1]  [3.3, 3.3] 
              12:46:28.3 - 12:48:11.7    54     10 NEPTUNE                  15016  [0,1]  [3.3, 3.3] 
              13:00:28.3 - 13:02:11.6    55      6 1411+522                 19954  [0,1]  [3.3, 3.3] 
              13:15:21.6 - 13:17:11.7    56      9 NGC7027                  19732  [0,1]  [3.3, 3.3] 
              13:33:41.6 - 13:35:41.6    57     11 URANUS                   20576  [0,1]  [3.3, 3.3] 
              13:44:28.3 - 13:46:11.6    58     10 NEPTUNE                  15026  [0,1]  [3.3, 3.3] 
              14:00:45.0 - 14:01:41.6    59      0 0137+331                  8380  [0,1]  [3.3, 3.3] 
              14:10:38.3 - 14:12:11.6    60     12 JUPITER                  15324  [0,1]  [3.3, 3.3] 
              14:24:05.0 - 14:25:41.7    61     11 URANUS                   18528  [0,1]  [3.3, 3.3] 
              14:34:28.4 - 14:36:11.7    62     10 NEPTUNE                  21050  [0,1]  [3.3, 3.3] 
              14:59:11.7 - 15:00:01.6    63      0 0137+331                  8576  [0,1]  [3.3, 3.3] 
              15:09:01.7 - 15:10:41.7    64     12 JUPITER                  19802  [0,1]  [3.3, 3.3] 
              15:24:28.3 - 15:26:21.7    65      9 NGC7027                  19518  [0,1]  [3.3, 3.3] 
              15:40:08.3 - 15:45:01.6    66     11 URANUS                   18910  [0,1]  [3.3, 3.3] 
              15:53:48.3 - 15:55:21.6    67     10 NEPTUNE                  19384  [0,1]  [3.3, 3.3] 
              16:18:51.8 - 16:19:51.6    68      0 0137+331                  9980  [0,1]  [3.3, 3.3] 
              16:29:08.4 - 16:30:51.6    69     12 JUPITER                  20634  [0,1]  [3.3, 3.3] 
              16:42:51.7 - 16:44:31.6    70     11 URANUS                   19574  [0,1]  [3.3, 3.3] 
              16:54:51.7 - 16:56:41.6    71      9 NGC7027                  21448  [0,1]  [3.3, 3.3] 
              17:23:05.0 - 17:30:41.6    72      2 0542+498                 60338  [0,1]  [3.3, 3.3] 
              17:41:48.4 - 17:43:21.7    73      3 0437+296                 19058  [0,1]  [3.3, 3.3] 
              17:55:35.0 - 17:57:41.6    74      4 VENUS                    19844  [0,1]  [3.3, 3.3] 
              18:19:21.6 - 18:20:11.6    75      0 0137+331                  8490  [0,1]  [3.3, 3.3] 
              18:30:21.6 - 18:32:01.7    76     12 JUPITER                  19516  [0,1]  [3.3, 3.3] 
              18:44:48.3 - 18:46:31.6    77      9 NGC7027                  19952  [0,1]  [3.3, 3.3] 
              18:59:11.7 - 19:01:01.6    78      2 0542+498                 20482  [0,1]  [3.3, 3.3] 
              19:19:08.4 - 19:21:21.7    79      5 0521+166                 20228  [0,1]  [3.3, 3.3] 
              19:32:48.4 - 19:34:31.6    80      3 0437+296                 19506  [0,1]  [3.3, 3.3] 
              19:39:01.7 - 19:40:41.7    81      4 VENUS                    19106  [0,1]  [3.3, 3.3] 
              20:08:05.0 - 20:09:01.6    82      0 0137+331                 10468  [0,1]  [3.3, 3.3] 
              20:18:08.4 - 20:19:51.7    83     12 JUPITER                  21480  [0,1]  [3.3, 3.3] 
              20:33:51.6 - 20:35:41.7    84      1 0813+482                 15666  [0,1]  [3.3, 3.3] 
              20:40:58.3 - 20:42:41.6    85      2 0542+498                 21522  [0,1]  [3.3, 3.3] 
              21:00:15.0 - 21:02:21.7    86      5 0521+166                 19586  [0,1]  [3.3, 3.3] 
              21:13:51.7 - 21:15:31.6    87      3 0437+296                 19072  [0,1]  [3.3, 3.3] 
              21:20:41.7 - 21:22:31.6    88      4 VENUS                    20792  [0,1]  [3.3, 3.3] 
              21:47:25.0 - 21:48:21.7    89      0 0137+331                 10478  [0,1]  [3.3, 3.3] 
              21:57:28.3 - 21:59:11.7    90     12 JUPITER                  17994  [0,1]  [3.3, 3.3] 
              22:12:11.6 - 22:14:01.7    91      2 0542+498                 20752  [0,1]  [3.3, 3.3] 
              22:28:31.7 - 22:30:21.6    92      4 VENUS                    20162  [0,1]  [3.3, 3.3] 
              22:53:31.6 - 22:54:21.6    93      0 0137+331                  8356  [0,1]  [3.3, 3.3] 
           (nRows = Total number of rows per scan) 
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:
  ID   Name  Station   Diam.    Long.         Lat.                Offset from array center (m)                ITRF Geocentric coordinates (m)        
                                                                     East         North     Elevation               x               y               z
  0    1     VLA:W9    25.0 m   -107.36.52.1  +33.53.47.7        356.6676     -433.6626      225.1132 -1600975.158364 -5042494.107339  3554641.463172
  1    2     VLA:N9    25.0 m   -107.37.15.4  +33.54.11.9       -240.2897      313.4933      393.6539 -1601460.354854 -5042049.553468  3555355.644885
  2    3     VLA:N3    25.0 m   -107.37.06.7  +33.54.04.2        -17.4692       74.9714       99.6712 -1601214.397725 -5042011.251852  3554993.689372
  3    4     VLA:N5    25.0 m   -107.37.08.7  +33.54.05.9        -68.1751      129.2172      166.5864 -1601270.378184 -5042020.000342  3555076.037288
  4    5     VLA:N2    25.0 m   -107.37.05.9  +33.54.03.5          2.8076       53.2529       72.9164 -1601192.017162 -5042007.769898  3554960.739959
  5    6     VLA:E1    25.0 m   -107.37.03.2  +33.54.01.1         71.0982      -20.0662      -17.3341 -1601116.634461 -5041996.020503  3554849.546756
  6    7     VLA:E2    25.0 m   -107.37.04.9  +33.54.02.8         28.4675       33.8392       -7.3941 -1601150.662703 -5041962.325383  3554899.832601
  7    8     VLA:N8    25.0 m   -107.37.13.4  +33.54.10.2       -190.6576      260.3978      328.2083 -1601405.572907 -5042041.036208  3555275.069191
  8    9     VLA:E8    25.0 m   -107.37.05.8  +33.54.06.1          6.2989      134.7733     -434.2193 -1601047.525515 -5041564.312882  3554745.537752
  9    10    VLA:W3    25.0 m   -107.37.02.9  +33.54.00.3         80.1203      -45.8643       64.8699 -1601133.041078 -5042077.495318  3554873.983114
  10   11    VLA:N1    25.0 m   -107.37.04.8  +33.54.02.5         30.6279       23.4333       36.2250 -1601161.318153 -5042003.016938  3554915.524518
  11   12    VLA:E6    25.0 m   -107.37.05.4  +33.54.04.7         16.2933       91.7808     -250.8566 -1601091.322144 -5041735.243504  3554812.129595
  12   13    VLA:W7    25.0 m   -107.36.56.5  +33.53.52.9        242.4927     -273.5855      158.9586 -1601040.352218 -5042322.124637  3554737.442512
  13   14    VLA:E4    25.0 m   -107.37.05.1  +33.54.03.6         23.5047       57.5697     -107.0769 -1601126.344551 -5041869.352053  3554863.929945
  14   15    VLA:N7    25.0 m   -107.37.11.7  +33.54.08.6       -145.3754      211.8883      268.4505 -1601355.591425 -5042033.262017  3555201.473230
  15   16    VLA:W4    25.0 m   -107.37.01.6  +33.53.58.8        111.6612      -90.1592       83.1040 -1601115.036739 -5042125.013009  3554847.387295
  16   17    VLA:W5    25.0 m   -107.37.00.2  +33.53.57.1        149.6513     -143.3993      105.1539 -1601093.353462 -5042182.256385  3554815.494412
  17   18    VLA:N6    25.0 m   -107.37.10.1  +33.54.07.2       -104.4709      168.0821      214.4514 -1601310.435141 -5042026.216445  3555134.993586
  18   19    VLA:E7    25.0 m   -107.37.05.5  +33.54.05.4         11.6554      112.2594     -337.9233 -1601070.412516 -5041654.078252  3554780.563218
  19   20    VLA:E9    25.0 m   -107.37.06.0  +33.54.06.9          0.6202      159.5263     -539.5994 -1601022.285439 -5041466.074026  3554707.303013
  21   22    VLA:W8    25.0 m   -107.36.54.4  +33.53.50.4        297.0182     -350.0344      190.5487 -1601009.218716 -5042404.256117  3554691.603703
  22   23    VLA:W6    25.0 m   -107.36.58.5  +33.53.55.1        193.2713     -204.5968      130.4320 -1601068.457362 -5042247.987272  3554778.796515
  23   24    VLA:W1    25.0 m   -107.37.04.0  +33.54.01.8         50.8529        1.6839        9.4260 -1601138.981029 -5041999.500238  3554882.525039
  24   25    VLA:W2    25.0 m   -107.37.03.8  +33.54.01.4         55.3249      -11.1030       50.4728 -1601147.188879 -5042040.122361  3554894.805680
  25   26    VLA:E5    25.0 m   -107.37.05.2  +33.54.04.1         20.1567       73.4368     -173.7487 -1601110.107707 -5041807.161867  3554839.912508
  26   27    VLA:N4    25.0 m   -107.37.07.5  +33.54.04.9        -37.7490       96.6657      126.4434 -1601236.789681 -5042014.759199  3555026.628473
  27   28    VLA:E3    25.0 m   -107.37.05.0  +33.54.03.2         26.2962       44.2582      -51.2014 -1601139.968101 -5041921.474667  3554884.046580


##########################################
##### 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              #####
##########################################

Next use plotants to check the array configuration and select 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')

Note (for uvfits sourced directly from archive only): CASA 5.4 and earlier versions will not plot the antennas properly. This is to be resolved in future CASA versions. If this occurs then a reference antenna can be selected using the listobs task and choosing an antenna located on a pad close to the center of the array (Pads numbers increase with distance from the center of the array, ie. "VLA:_N1" and "EVLA:W2" are pads close to the center of the array, where as, "VLA:_N18" is not).

Data Inspection and Flagging

In this section we present two methods of flagging the data:

• Interactive flagging using plotms, which is destructive to the data set and cannot be undone. If a mistake is made, you must start over with a new copy of the data set. Because of the destructive nature of this method, it is generally not recommended.

• Non-interactive flagging using flagdata, which is not destructive to the data set and can be undone (be sure to set flagbackup=True). If a mistake is made, you may undo the flagged data. This is the recommended approach to flagging any data set, new (JVLA) or old (VLA).

For both methods (interactive and non-interactive flagging), we will use plotms to inspect the data.

plotms(vis='jupiter6cm.demo.ms', selectdata=True, field='1331+305', correlation='RR,LL', xaxis='uvdist', yaxis='amp')

Inspect the following in the data set:

• The primary flux density scale and polarization angle calibrator, 1331+305 (3C286).
• RR,LL and RL,LR correlations separately due to large amplitude differences between them (when all correlations are plotted together, the RL,LR will seem like bad data due to their much lower amplitudes as compared to RR,LL).
• The other two sources we are interested in, the polarization leakage calibrator (0137+331) and the target source (JUPITER).

Interactive Flagging

• Use Mark Regions within the plotms GUI to draw boxes around points to flag, and hit Flag to flag.

Non-Interactive Flagging

• Use plotms to inspect the data set and flagdata to flag the data. While inspecting the data, you may notice that Antenna 9 (ID=8) in spw='1' is often bad. The bad data on Antenna 9 are in the last 4 scans in spw='1' for the 0137+331 calibrator and for the target source (JUPITER), as well as in the last scan for all antennas in both spws on the target source. We can flag these points with the following flagdata task executions.

flagdata(vis='jupiter6cm.demo.ms', mode='manual', field='0137+331', spw='1', antenna='9', timerange='42:00:00~48:00:00', flagbackup=True)
flagdata(vis='jupiter6cm.demo.ms', mode='manual', field='JUPITER', spw='1', antenna='9', timerange='16:26:00~22:20:00', flagbackup=True)
flagdata(vis='jupiter6cm.demo.ms', mode='manual', field='JUPITER', spw='', timerange='21:40:00~22:20:00', flagbackup=True)

• There are more data points to flag -- keep flagging until you are happy with the results. The following commands will get rid of most bad data, but depending on how clean the data you want to proceed with, you may still want to inspect them in plotms and flag interactively the remainder of bad data points.

flagdata(vis='jupiter6cm.demo.ms',mode='clip',field='1331+305',correlation='ABS_RR,LL',clipoutside=False,clipminmax=[0,0.75], flagbackup=True)
flagdata(vis='jupiter6cm.demo.ms',mode='clip',field='1331+305',correlation='ABS_RL,LR',clipoutside=False,clipminmax=[0,0.04], flagbackup=True)
flagdata(vis='jupiter6cm.demo.ms',mode='clip',field='0137+331',correlation='ABS_RR,LL',clipoutside=False,clipminmax=[0,0.55], flagbackup=True)
flagdata(vis='jupiter6cm.demo.ms',mode='clip',field='0137+331',correlation='ABS_RL,LR',clipoutside=False,clipminmax=[0,0.01], flagbackup=True)

If you are unfamiliar with flagging in CASA, consult the detailed topical guide Flagging VLA Data.

Calibration

Flux Density Scale

Next we will use setjy to set the absolute flux density scale, only for Stokes I at the moment (the total flux density model).

• Our primary flux calibrator here is 1331+305 (3C286).
• The default model for CASA 5.5+ is 'Perley-Butler 2017'.

setjy(vis='jupiter6cm.demo.ms', field='1331+305', model='3C286_C.im')

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 the different tables and their corresponding solutions (e.g., gain curve table = .gc).

NOTE: Since we have only two single-channel continuum spw, we do not want to do bandpass calibration nor solve for delays within spws as is currently done with wide bandwidth JVLA data.

First, 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 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
plotms(vis='jupiter6cm.demo.G', xaxis='time', yaxis='amp', gridrows=3, gridcols=3, iteraxis='antenna')
plotms(vis='jupiter6cm.demo.G', xaxis='time', yaxis='phase', plotrange=[-1,-1,-200,200], gridrows=3, gridcols=3, iteraxis='antenna')

If all looks good, bootstrap the flux density scale of the flux calibrator onto the phase calibrators (CASA's fluxscale task is equivalent to GETJY in AIPS). When executing fluxscale, the calibration table with the extension .G is modified and stored as a new table with the extension .Gflx.

myFluxscale = fluxscale(vis='jupiter6cm.demo.ms', caltable='jupiter6cm.demo.G', fluxtable='jupiter6cm.demo.Gflx', reference='1331+305', transfer='0137+331', incremental=True, 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: 5.29665 +/- 0.00449217 (SNR = 1179.09, N = 54)
 Flux density for 0137+331 in SpW=1 (freq=4.8351e+09 Hz) is: 5.34890 +/- 0.00176819 (SNR = 3025.07, N = 54)
 Fitted spectrum for 0137+331 with fitorder=1: Flux density = 5.32271 +/- 1.70229e-07 (freq=4.86004 GHz) spidx=-0.954124 (degenerate)
 Storing result in jupiter6cm.demo.Gflx
 Writing solutions to table: jupiter6cm.demo.Gflx

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

plotms(vis='jupiter6cm.demo.Gflx', xaxis='time', yaxis='amp', showgui=True, plotfile='jupiter6cm.demo.Gflx.amp.png')

plotms(vis='jupiter6cm.demo.Gflx', xaxis='time', yaxis='phase', plotrange=[-1,-1,-200,200], showgui=True, plotfile='jupiter6cm.demo.Gflx.phase.png')

Polarization Calibration

Just as in the step of the initial gain calibration, since our old VLA data have single-channel continuum spws, we do not want to solve for KCROSS delays in our polarization calibration. Instead, we directly solve for D and X terms.

Set the Polarization Model

First, set the polarization model for the polarized position-angle calibrator (here 1331+305=3C286 which is also our primary flux calibrator). For polarization properties of your primary polarization calibrator see the Polarimetry section of the VLA Observing 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 # Polarization angle 33deg in radians

myPolSetjy = setjy(vis='jupiter6cm.demo.ms', field='1331+305', standard='manual', spw='', 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 saved in the myPolSetjy python dictionary

#In CASA
CASA <49>: myPolSetjy
Out[49]: 
{'7': {'0': {'fluxd': array([ 7.3109    ,  0.33899165,  0.7613877 ,  0.        ])},
  '1': {'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. In this step we solve for the instrumental polarization. We will assume here our calibrator has unknown polarization (poltype='D+QU' if good parallactic coverage, otherwise poltype='D', consult polcal for more information on options).

polcal(vis='jupiter6cm.demo.ms', caltable='jupiter6cm.demo.D', field='0137+331', spw='', refant='11', poltype='D+QU', solint='inf', combine='scan',minsnr=3, gaintable=['jupiter6cm.demo.gc', 'jupiter6cm.demo.G'], gainfield=['','0137+331',''])

Check the solutions

plotms(vis='jupiter6cm.demo.D', xaxis='antenna', yaxis='amp', showgui=True, plotfile='jupiter6cm.demo.D.amp.png')

plotms(vis='jupiter6cm.demo.D', xaxis='antenna', yaxis='phase', plotrange=[-1,-1,-200,200], showgui=True, plotfile='jupiter6cm.demo.D.phase.png')

plotms(vis='jupiter6cm.demo.D', xaxis='antenna', yaxis='snr', showgui=True, plotfile='jupiter6cm.demo.D.snr.png')

Solve for the R-L Polarization angle (X term)

The total polarization is now correct (since we just calibrated the instrumental polarization, i.e., D terms). Now the R-L phase needs to be calibrated to obtain an accurate polarization position angle.

polcal(vis='jupiter6cm.demo.ms', caltable='jupiter6cm.demo.X', field='1331+305', spw='', refant='11', poltype='Xf', solint='inf', combine='scan',minsnr=3, gaintable=['jupiter6cm.demo.gc', 'jupiter6cm.demo.G', 'jupiter6cm.demo.D'], gainfield=['','1331+305','',''])

Check the solutions in the CASA logger window

The following calibration term is arranged for solve:
.   Xf Jones: table=jupiter6cm.demo.X append=false solint=inf,none refantmode='flex' refant='none' minsnr=3 apmode=AP solnorm=false
For solint = inf, found 2 solution intervals.
Mean position angle offset solution for 1331+305 (spw = 0) = 80.7525 deg.
Mean position angle offset solution for 1331+305 (spw = 1) = 48.9853 deg.
  Found good Xf Jones solutions in 2 solution intervals.

NOTE: If you are using CASA 4.7 or earlier, you may want to use poltype='X' in X-term calculations (Mueller matrices). For CASA 5.0 and later this option will not work (the relevant CASA documentation is being updated), and hence you need to use poltype='Xf' (Jones matrices). Although 'Xf' should be used predominantly for large bandwidths, which clearly is not the case here, it can also be used for the single channel old VLA data as long as you make sure the interp parameter is set to default (which should be nearest).

Apply the Calibration

Now that we have derived all the calibration solutions and saved them in the tables of multiple extensions, we need to apply them to the actual data. The applycal task commands will apply the solution tables to the DATA and write a new column CORRECTED_DATA as it is standard for CASA. Important: make sure you set parang=True.

applycal(vis='jupiter6cm.demo.ms', field='1331+305', spw='', selectdata=False, gaintable=['jupiter6cm.demo.gc', 'jupiter6cm.demo.G', 'jupiter6cm.demo.D','jupiter6cm.demo.X'], gainfield=['','1331+305'], calwt=[False], parang=True)

applycal(vis='jupiter6cm.demo.ms', field='0137+331', spw='', selectdata=False, gaintable=['jupiter6cm.demo.gc', 'jupiter6cm.demo.G', 'jupiter6cm.demo.Gflx','jupiter6cm.demo.D','jupiter6cm.demo.X'], gainfield=['','0137+331','0137+331'], calwt=[False], parang=True)

applycal(vis='jupiter6cm.demo.ms', field='JUPITER', spw='', selectdata=False, gaintable=['jupiter6cm.demo.gc', 'jupiter6cm.demo.G', 'jupiter6cm.demo.Gflx','jupiter6cm.demo.D','jupiter6cm.demo.X'], gainfield=['','0137+331','0137+331'], calwt=[False], parang=True)

Next, we will split the corrected (i.e., calibrated) Jupiter target data from the MS we started with and write it to a new single-source MS.

split(vis='jupiter6cm.demo.ms', outputvis='jupiter6cm.demo.JUPITER.split.ms', field='JUPITER', datacolumn='corrected')

You can use the plotms task to look at the split calibrated data.

Initial Imaging (Stokes I)

Next we will image and clean the Jupiter data. In this step we will self-calibrate, therefore in the initial imaging we will not clean too deeply and we will save the model in the MS data (with the use of parameter savemodel in tclean).

Since we set mask="" in tclean, the interactive GUI will not allow you to do the deconvolution before you draw the mask on at least one plane. When drawing a mask, make sure to extend it to all channels and all polarization.

tclean(vis='jupiter6cm.demo.JUPITER.split.ms', stokes='I', field='', spw='', imagename='jupiter6cm.demo.JUPITER.I.clean1', robust = 0.0, imsize=[288], cell=['3arcsec'], specmode='mfs', deconvolver='hogbom', weighting='briggs', threshold='0.1mJy', mask='', niter=500, interactive=True, cycleniter=100, savemodel='modelcolumn', pblimit=-0.2)

Inspect the quality of the cleaned images with imstat.

imstat(imagename='jupiter6cm.demo.JUPITER.I.clean1.image', stokes='I', box='216,1,287,72')

In this initial imaging, the deconvolution will stop with the iteration limit since we set it fairly low. We 'cleaned' approximately 4.3 Jy in this initial imaging step, and reached rms of about 3.52 mJy/bm.

Self-Calibration

In the self-calibration step we run gaincal that will make use of the newly created MODEL column in our MS file.

gaincal(vis='jupiter6cm.demo.JUPITER.split.ms', caltable='jupiter6cm.demo.JUPITER.split.selfcal1', field='', spw='', gaintype='G', calmode='p', solint='30s', combine='', refant='11', parang=False, append=False, selectdata=False)

Inspect the solutions using plotms.

plotms(vis='jupiter6cm.demo.JUPITER.split.selfcal1',xaxis='time',yaxis='amp',gridrows=2, gridcols=3, iteraxis='antenna')
plotms(vis='jupiter6cm.demo.JUPITER.split.selfcal1',xaxis='time',yaxis='phase', gridrows=2, gridcols=3 ,iteraxis='antenna',plotrange=[-1,-1,-180,180])

Next, use applycal to apply the calibration to the DATA (creating a CORRECTED column in the MS).

applycal(vis='jupiter6cm.demo.JUPITER.split.ms', field='', spw='', selectdata=False, gaintable=['jupiter6cm.demo.JUPITER.split.selfcal1'], gainfield=[''], interp=['nearest'],calwt=[False], applymode='calflag')

Now, use tclean to image the self-calibrated data.

tclean(vis='jupiter6cm.demo.JUPITER.split.ms', stokes='I', field='', spw='', imagename='jupiter6cm.demo.JUPITER.I.clean2', robust= 0.0, imsize=[288], cell=['3arcsec'], specmode='mfs', deconvolver='hogbom', weighting='briggs', threshold='0.05mJy', mask='', niter=10000, interactive=True, cycleniter=100, pblimit=-0.2)

Check the image statistics using imstat.

imstat(imagename='jupiter6cm.demo.JUPITER.I.clean2.image', stokes='I', box='216,1,287,72')

After one cycle of self-calibration with tclean we reached rms=1.10 mJy/bm. However, keep in mind that the rms values may differ for you since they will depend on how deeply you cleaned and how good a mask you applied.

Full Stokes Imaging

At this stage we will perform full Stokes imaging using tclean to create an image of each Stokes parameter that we will later use to create polarized intensity and angle images.

tclean(vis='jupiter6cm.demo.JUPITER.split.ms', stokes='IQUV', field='', spw='', imagename='jupiter6cm.demo.JUPITER.IQUV.clean', robust= 0.0, imsize=[288], cell=['3arcsec'], specmode='mfs', deconvolver='clarkstokes', weighting='briggs', threshold='0.05mJy', mask='', niter=10000, interactive=True, cycleniter=100, pblimit=-0.2)

Inspect the quality of the cleaned images with imstat. Do so for each Stokes separately, otherwise imstat will return an average of all Stokes.

You should be reaching values of about:

• 1.1 mJy/bm (I)
• 0.62 mJy/bm (Q)
• 0.90 mJy/bm (U)
• 0.16 mJy/bm (V)

Polarization Intensity and Position Angle Images

Polarized intensity (POLI) image of Jupiter with overlaid polarized angle vectors (POLA).

Total continuum intensity (Stokes I) image of Jupiter with overlaid contours of its polarized intensity (POLI).

Next, we will save each Stokes plane as separate images. We can use either the imsubimage or immath tasks to do so.

Run the imsubimage task:

imsubimage(imagename='jupiter6cm.demo.JUPITER.IQUV.clean.image',outfile='JUPITER.I.image',stokes='I')
imsubimage(imagename='jupiter6cm.demo.JUPITER.IQUV.clean.image',outfile='JUPITER.Q.image',stokes='Q')
imsubimage(imagename='jupiter6cm.demo.JUPITER.IQUV.clean.image',outfile='JUPITER.U.image',stokes='U')

Or run the immath task:

immath(imagename='jupiter6cm.demo.JUPITER.IQUV.clean.image', mode='evalexpr', stokes='I', expr='IM0', outfile='JUPITER.I.image')
immath(imagename='jupiter6cm.demo.JUPITER.IQUV.clean.image', mode='evalexpr', stokes='Q', expr='IM0', outfile='JUPITER.Q.image')
immath(imagename='jupiter6cm.demo.JUPITER.IQUV.clean.image', mode='evalexpr', stokes='U', expr='IM0', outfile='JUPITER.U.image')

Finally, we want to create the polarization intensity (POLI) and position angle (POLA) images using immath.

immath(imagename=['JUPITER.Q.image','JUPITER.U.image'], mode='poli', outfile='JUPITER.POLI.image')

We will now use the polithresh parameter when creating the polarization angle image to get rid of the noise. First check the statistic in the POLI image, and then use it as a threshold while creating the POLA image (in the example below equal to 4 sigma).

imstat(imagename='JUPITER.POLI.image', box='216,1,287,72')

immath(imagename=['JUPITER.Q.image','JUPITER.U.image'], mode='pola', outfile='JUPITER.POLA.image',polithresh='4.5mJy/beam')

Again, check the statistics of these final images with imstat and/or CARTA. (Note, CARTA is replacing the viewer task.)

That concludes this tutorial.

For the tutorial on how to perform analysis, display, and manipulation of the polarization images, consult the VLA Continuum Tutorial 3C391.

Last checked on CASA Version 6.4.1

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