VLA CASA Bandpass Slope-CASA4.5.2

This CASA Guide is for CASA version 4.5.2

Overview

For the standard VLA flux calibrators, CASA includes a spatial and spectral model that is being applied for the and bandpass calibration. This model takes out the source characteristics and calibration solution then represent the instrument and atmospheric corrections. The VLA standards, however, have a relatively steep spectral index and are relatively weak at high frequencies. Although this is usually not a problem for absolute flux calibration, a good bandpass determination requires a very strong source, particularly for narrow channel widths. So for the high frequency, narrow channel case it is thus advisable to observe a different, but very strong source to correct for the bandpass. Such sources typically are variable and show a spectral slope that needs to be corrected for when the bandwidth is large. This tutorial describes how to model such a slope and correct the bandpass solution for it.

Data is taken in wide, 3-bit mode for the protostar G192.16-3.84 in Ka-band with spectral windows centered 29 and 36.5 GHz Each baseband has over 4 GHz of bandwidth comprised of 32 128-MHz spectral windows.

This is a more advanced tutorial, so if you are a relative novice, it is strongly recommended that you start with the EVLA Continuum Tutorial 3C391 (at least read it through), or even Getting Started in CASA before proceeding with this tutorial.

Obtaining the Data

As this tutorial concerns bandpass solutions only, we removed all other sources from the MS and only keep the bandpass calibrator scans. We also applied flagging and all pre-calibration steps including antenna position offsets, requantizer gains, opacity corrections, and gain-elevation curves. The original data (TVER0004.sb14459364.eb14492359.56295.26287841435) can be obtained through the [NRAO archive] and has a raw size of 57.04 GB.

The trimmed measurement set can be downloaded directly from http://casa.nrao.edu/Data/EVLA/G192/G192-BP.ms.tar.gz (dataset size: 2.1 GB)

Your first step will be to unzip and untar the file in a terminal (before you start CASA):

tar -xzvf G192-BP.ms.tar.gz

Starting CASA

As usual, to start CASA, type:

casa

This will run a script to initialize CASA, setting paths appropriately. It will also start writing to a file called ipython-<unique-stamp>.log, which will contain a record of all the text you enter at the CASA prompt, as well as casapy-<unique-stamp>.log, which will contain all the messages that are printed to the CASA logger window. It is recommended that you keep your log files in tact - you may need them to remind you of the last step you completed in your data reduction! (It is also a good idea to include your log files when submitting a help desk ticket).

Once CASA has started, a logger window will appear. Note that you can rescale this window or change the font size as desired (the latter is under "View").

Examining the Measurement Set (MS)

We use listobs to summarize our MS:

# In CASA: listobs on the initial data set
listobs('G192-BP.ms', listfile='G192_listobs.txt')

This will write the output to a file called G192_listobs.txt, which we can print to the terminal using the cat command:

# In CASA
cat G192_listobs.txt

================================================================================
           MeasurementSet Name:  /lustre/aoc/sciops/jott/casa/topicalguide/bandpass/G192-BP.ms      MS Version 2
================================================================================
   Observer: Dr. Debra Shepherd     Project: uid://evla/pdb/7303457  
Observation: EVLA
Data records: 1064490       Total elapsed time = 444 seconds
   Observed from   03-Jan-2013/07:40:27.0   to   03-Jan-2013/07:47:51.0 (UTC)

   ObservationID = 0         ArrayID = 0
  Date        Timerange (UTC)          Scan  FldId FieldName             nRows     SpwIds   Average Interval(s)    ScanIntent
  03-Jan-2013/07:40:27.0 - 07:47:51.0    64      0 3c84-J0319+413         1064490  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63]  [6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6] [CALIBRATE_BANDPASS#UNSPECIFIED,OBSERVE_TARGET#UNSPECIFIED]
           (nRows = Total number of rows per scan) 
Fields: 1
  ID   Code Name                RA               Decl           Epoch   SrcId      nRows
  0    F    3c84-J0319+413      03:19:48.160102 +41.30.42.10305 J2000   0        1064490
Spectral Windows:  (64 unique spectral windows and 1 unique polarization setups)
  SpwID  Name            #Chans   Frame   Ch0(MHz)  ChanWid(kHz)  TotBW(kHz) CtrFreq(MHz) BBC Num  Corrs  
  0      EVLA_KA#A1C1#2     128   TOPO   34476.000      1000.000    128000.0  34539.5000       10  RR  LL
  1      EVLA_KA#A1C1#3     128   TOPO   34604.000      1000.000    128000.0  34667.5000       10  RR  LL
  2      EVLA_KA#A1C1#4     128   TOPO   34732.000      1000.000    128000.0  34795.5000       10  RR  LL
  3      EVLA_KA#A1C1#5     128   TOPO   34860.000      1000.000    128000.0  34923.5000       10  RR  LL
  4      EVLA_KA#A1C1#6     128   TOPO   34988.000      1000.000    128000.0  35051.5000       10  RR  LL
  5      EVLA_KA#A1C1#7     128   TOPO   35116.000      1000.000    128000.0  35179.5000       10  RR  LL
  6      EVLA_KA#A1C1#8     128   TOPO   35244.000      1000.000    128000.0  35307.5000       10  RR  LL
  7      EVLA_KA#A1C1#9     128   TOPO   35372.000      1000.000    128000.0  35435.5000       10  RR  LL
  8      EVLA_KA#A1C1#10    128   TOPO   35500.000      1000.000    128000.0  35563.5000       10  RR  LL
  9      EVLA_KA#A1C1#11    128   TOPO   35628.000      1000.000    128000.0  35691.5000       10  RR  LL
  10     EVLA_KA#A1C1#12    128   TOPO   35756.000      1000.000    128000.0  35819.5000       10  RR  LL
  11     EVLA_KA#A1C1#13    128   TOPO   35884.000      1000.000    128000.0  35947.5000       10  RR  LL
  12     EVLA_KA#A1C1#14    128   TOPO   36012.000      1000.000    128000.0  36075.5000       10  RR  LL
  13     EVLA_KA#A1C1#15    128   TOPO   36140.000      1000.000    128000.0  36203.5000       10  RR  LL
  14     EVLA_KA#A1C1#16    128   TOPO   36268.000      1000.000    128000.0  36331.5000       10  RR  LL
  15     EVLA_KA#A1C1#17    128   TOPO   36396.000      1000.000    128000.0  36459.5000       10  RR  LL
  16     EVLA_KA#A2C2#18    128   TOPO   36476.000      1000.000    128000.0  36539.5000       11  RR  LL
  17     EVLA_KA#A2C2#19    128   TOPO   36604.000      1000.000    128000.0  36667.5000       11  RR  LL
  18     EVLA_KA#A2C2#20    128   TOPO   36732.000      1000.000    128000.0  36795.5000       11  RR  LL
  19     EVLA_KA#A2C2#21    128   TOPO   36860.000      1000.000    128000.0  36923.5000       11  RR  LL
  20     EVLA_KA#A2C2#22    128   TOPO   36988.000      1000.000    128000.0  37051.5000       11  RR  LL
  21     EVLA_KA#A2C2#23    128   TOPO   37116.000      1000.000    128000.0  37179.5000       11  RR  LL
  22     EVLA_KA#A2C2#24    128   TOPO   37244.000      1000.000    128000.0  37307.5000       11  RR  LL
  23     EVLA_KA#A2C2#25    128   TOPO   37372.000      1000.000    128000.0  37435.5000       11  RR  LL
  24     EVLA_KA#A2C2#26    128   TOPO   37500.000      1000.000    128000.0  37563.5000       11  RR  LL
  25     EVLA_KA#A2C2#27    128   TOPO   37628.000      1000.000    128000.0  37691.5000       11  RR  LL
  26     EVLA_KA#A2C2#28    128   TOPO   37756.000      1000.000    128000.0  37819.5000       11  RR  LL
  27     EVLA_KA#A2C2#29    128   TOPO   37884.000      1000.000    128000.0  37947.5000       11  RR  LL
  28     EVLA_KA#A2C2#30    128   TOPO   38012.000      1000.000    128000.0  38075.5000       11  RR  LL
  29     EVLA_KA#A2C2#31    128   TOPO   38140.000      1000.000    128000.0  38203.5000       11  RR  LL
  30     EVLA_KA#A2C2#32    128   TOPO   38268.000      1000.000    128000.0  38331.5000       11  RR  LL
  31     EVLA_KA#A2C2#33    128   TOPO   38396.000      1000.000    128000.0  38459.5000       11  RR  LL
  32     EVLA_KA#B1D1#34    128   TOPO   26976.000      1000.000    128000.0  27039.5000       13  RR  LL
  33     EVLA_KA#B1D1#35    128   TOPO   27104.000      1000.000    128000.0  27167.5000       13  RR  LL
  34     EVLA_KA#B1D1#36    128   TOPO   27232.000      1000.000    128000.0  27295.5000       13  RR  LL
  35     EVLA_KA#B1D1#37    128   TOPO   27360.000      1000.000    128000.0  27423.5000       13  RR  LL
  36     EVLA_KA#B1D1#38    128   TOPO   27488.000      1000.000    128000.0  27551.5000       13  RR  LL
  37     EVLA_KA#B1D1#39    128   TOPO   27616.000      1000.000    128000.0  27679.5000       13  RR  LL
  38     EVLA_KA#B1D1#40    128   TOPO   27744.000      1000.000    128000.0  27807.5000       13  RR  LL
  39     EVLA_KA#B1D1#41    128   TOPO   27872.000      1000.000    128000.0  27935.5000       13  RR  LL
  40     EVLA_KA#B1D1#42    128   TOPO   28000.000      1000.000    128000.0  28063.5000       13  RR  LL
  41     EVLA_KA#B1D1#43    128   TOPO   28128.000      1000.000    128000.0  28191.5000       13  RR  LL
  42     EVLA_KA#B1D1#44    128   TOPO   28256.000      1000.000    128000.0  28319.5000       13  RR  LL
  43     EVLA_KA#B1D1#45    128   TOPO   28384.000      1000.000    128000.0  28447.5000       13  RR  LL
  44     EVLA_KA#B1D1#46    128   TOPO   28512.000      1000.000    128000.0  28575.5000       13  RR  LL
  45     EVLA_KA#B1D1#47    128   TOPO   28640.000      1000.000    128000.0  28703.5000       13  RR  LL
  46     EVLA_KA#B1D1#48    128   TOPO   28768.000      1000.000    128000.0  28831.5000       13  RR  LL
  47     EVLA_KA#B1D1#49    128   TOPO   28896.000      1000.000    128000.0  28959.5000       13  RR  LL
  48     EVLA_KA#B2D2#50    128   TOPO   28976.000      1000.000    128000.0  29039.5000       14  RR  LL
  49     EVLA_KA#B2D2#51    128   TOPO   29104.000      1000.000    128000.0  29167.5000       14  RR  LL
  50     EVLA_KA#B2D2#52    128   TOPO   29232.000      1000.000    128000.0  29295.5000       14  RR  LL
  51     EVLA_KA#B2D2#53    128   TOPO   29360.000      1000.000    128000.0  29423.5000       14  RR  LL
  52     EVLA_KA#B2D2#54    128   TOPO   29488.000      1000.000    128000.0  29551.5000       14  RR  LL
  53     EVLA_KA#B2D2#55    128   TOPO   29616.000      1000.000    128000.0  29679.5000       14  RR  LL
  54     EVLA_KA#B2D2#56    128   TOPO   29744.000      1000.000    128000.0  29807.5000       14  RR  LL
  55     EVLA_KA#B2D2#57    128   TOPO   29872.000      1000.000    128000.0  29935.5000       14  RR  LL
  56     EVLA_KA#B2D2#58    128   TOPO   30000.000      1000.000    128000.0  30063.5000       14  RR  LL
  57     EVLA_KA#B2D2#59    128   TOPO   30128.000      1000.000    128000.0  30191.5000       14  RR  LL
  58     EVLA_KA#B2D2#60    128   TOPO   30256.000      1000.000    128000.0  30319.5000       14  RR  LL
  59     EVLA_KA#B2D2#61    128   TOPO   30384.000      1000.000    128000.0  30447.5000       14  RR  LL
  60     EVLA_KA#B2D2#62    128   TOPO   30512.000      1000.000    128000.0  30575.5000       14  RR  LL
  61     EVLA_KA#B2D2#63    128   TOPO   30640.000      1000.000    128000.0  30703.5000       14  RR  LL
  62     EVLA_KA#B2D2#64    128   TOPO   30768.000      1000.000    128000.0  30831.5000       14  RR  LL
  63     EVLA_KA#B2D2#65    128   TOPO   30896.000      1000.000    128000.0  30959.5000       14  RR  LL
Sources: 64
  ID   Name                SpwId RestFreq(MHz)  SysVel(km/s) 
  0    3c84-J0319+413      0     -              -            
  0    3c84-J0319+413      1     -              -            
  0    3c84-J0319+413      2     -              -            
  0    3c84-J0319+413      3     -              -            
  0    3c84-J0319+413      4     -              -            
  0    3c84-J0319+413      5     -              -            
  0    3c84-J0319+413      6     -              -            
  0    3c84-J0319+413      7     -              -            
  0    3c84-J0319+413      8     -              -            
  0    3c84-J0319+413      9     -              -            
  0    3c84-J0319+413      10    -              -            
  0    3c84-J0319+413      11    -              -            
  0    3c84-J0319+413      12    -              -            
  0    3c84-J0319+413      13    -              -            
  0    3c84-J0319+413      14    -              -            
  0    3c84-J0319+413      15    -              -            
  0    3c84-J0319+413      16    -              -            
  0    3c84-J0319+413      17    -              -            
  0    3c84-J0319+413      18    -              -            
  0    3c84-J0319+413      19    -              -            
  0    3c84-J0319+413      20    -              -            
  0    3c84-J0319+413      21    -              -            
  0    3c84-J0319+413      22    -              -            
  0    3c84-J0319+413      23    -              -            
  0    3c84-J0319+413      24    -              -            
  0    3c84-J0319+413      25    -              -            
  0    3c84-J0319+413      26    -              -            
  0    3c84-J0319+413      27    -              -            
  0    3c84-J0319+413      28    -              -            
  0    3c84-J0319+413      29    -              -            
  0    3c84-J0319+413      30    -              -            
  0    3c84-J0319+413      31    -              -            
  0    3c84-J0319+413      32    -              -            
  0    3c84-J0319+413      33    -              -            
  0    3c84-J0319+413      34    -              -            
  0    3c84-J0319+413      35    -              -            
  0    3c84-J0319+413      36    -              -            
  0    3c84-J0319+413      37    -              -            
  0    3c84-J0319+413      38    -              -            
  0    3c84-J0319+413      39    -              -            
  0    3c84-J0319+413      40    -              -            
  0    3c84-J0319+413      41    -              -            
  0    3c84-J0319+413      42    -              -            
  0    3c84-J0319+413      43    -              -            
  0    3c84-J0319+413      44    -              -            
  0    3c84-J0319+413      45    -              -            
  0    3c84-J0319+413      46    -              -            
  0    3c84-J0319+413      47    -              -            
  0    3c84-J0319+413      48    -              -            
  0    3c84-J0319+413      49    -              -            
  0    3c84-J0319+413      50    -              -            
  0    3c84-J0319+413      51    -              -            
  0    3c84-J0319+413      52    -              -            
  0    3c84-J0319+413      53    -              -            
  0    3c84-J0319+413      54    -              -            
  0    3c84-J0319+413      55    -              -            
  0    3c84-J0319+413      56    -              -            
  0    3c84-J0319+413      57    -              -            
  0    3c84-J0319+413      58    -              -            
  0    3c84-J0319+413      59    -              -            
  0    3c84-J0319+413      60    -              -            
  0    3c84-J0319+413      61    -              -            
  0    3c84-J0319+413      62    -              -            
  0    3c84-J0319+413      63    -              -            
Antennas: 22:
  ID   Name  Station   Diam.    Long.         Lat.                Offset from array center (m)                ITRF Geocentric coordinates (m)        
                                                                     East         North     Elevation               x               y               z
  1    ea02  N56       25.0 m   -107.37.47.9  +34.00.38.4      -1105.2071    12254.3069      -34.2426 -1600128.383400 -5035104.146500  3565024.672100
  2    ea03  N16       25.0 m   -107.37.10.9  +33.54.48.0       -155.8511     1426.6436       -9.3827 -1601061.956000 -5041175.880700  3556058.037600
  3    ea05  W08       25.0 m   -107.37.21.6  +33.53.53.0       -432.1184     -272.1472       -1.5070 -1601614.092200 -5042001.650900  3554652.508900
  4    ea06  N32       25.0 m   -107.37.22.0  +33.56.33.6       -441.7237     4689.9748      -16.9332 -1600781.042100 -5039347.435200  3558761.533000
  5    ea07  E40       25.0 m   -107.32.35.4  +33.52.16.9       6908.8279    -3240.7316       39.0057 -1595124.924100 -5045829.461500  3552210.685200
  6    ea09  E24       25.0 m   -107.35.13.4  +33.53.18.1       2858.1754    -1349.1257       13.7290 -1598663.097500 -5043581.389700  3553767.027800
  8    ea11  W56       25.0 m   -107.44.26.7  +33.49.54.6     -11333.2153    -7637.6824       15.3542 -1613255.404300 -5042613.085000  3548545.901400
  9    ea12  E08       25.0 m   -107.36.48.9  +33.53.55.1        407.8285     -206.0065       -3.2272 -1600801.926000 -5042219.366500  3554706.448200
  11   ea14  W16       25.0 m   -107.37.57.4  +33.53.33.0      -1348.7083     -890.6269        1.3068 -1602592.853600 -5042055.005300  3554140.703900
  12   ea15  W72       25.0 m   -107.48.24.0  +33.47.41.2     -17419.4730   -11760.2869       14.9578 -1619757.314900 -5042937.673700  3545120.385300
  13   ea16  N08       25.0 m   -107.37.07.5  +33.54.15.8        -68.9252      433.1901       -5.0683 -1601147.956700 -5041733.824100  3555235.952500
  14   ea17  E48       25.0 m   -107.30.56.1  +33.51.38.4       9456.5938    -4431.6366       37.9317 -1592894.088800 -5047229.121000  3551221.221100
  15   ea18  E72       25.0 m   -107.24.42.3  +33.49.18.0      19041.8754    -8769.2059        4.7234 -1584460.867200 -5052385.599300  3547599.997600
  17   ea20  N72       25.0 m   -107.38.10.5  +34.04.12.2      -1685.6775    18861.8403      -43.4734 -1599557.932000 -5031396.371000  3570494.760600
  18   ea21  E64       25.0 m   -107.27.00.1  +33.50.06.7      15507.6045    -7263.7280       67.1961 -1587600.190400 -5050575.873800  3548885.396600
  19   ea22  N24       25.0 m   -107.37.16.1  +33.55.37.7       -290.3745     2961.8582      -12.2374 -1600930.087700 -5040316.398500  3557330.387000
  20   ea23  N64       25.0 m   -107.37.58.7  +34.02.20.5      -1382.3750    15410.1463      -40.6373 -1599855.675100 -5033332.371000  3567636.622500
  21   ea24  W40       25.0 m   -107.41.13.5  +33.51.43.1      -6377.9740    -4286.7919        8.2191 -1607962.456900 -5042338.214500  3551324.943600
  22   ea25  W48       25.0 m   -107.42.44.3  +33.50.52.1      -8707.9407    -5861.7854       15.5265 -1610451.925400 -5042471.123100  3550021.056800
  23   ea26  W32       25.0 m   -107.39.54.8  +33.52.27.2      -4359.4561    -2923.1223       11.7579 -1605808.647100 -5042230.071500  3552459.203400
  24   ea27  E16       25.0 m   -107.36.09.8  +33.53.40.0       1410.0316     -673.4696       -0.7909 -1599926.110000 -5042772.967300  3554319.791200
  25   ea28  N40       25.0 m   -107.37.29.5  +33.57.44.4       -633.6167     6878.5984      -20.7748 -1600592.764000 -5038121.352000  3560574.847300

We have trimmed to MS to contain only one scan on the bandpass calibrator 3C84, but retained all 64 spectral windows, each 128MHz wide and containing 128 1MHz channels.

Calibrating delays and initial bandpass solutions

As a first step, we use an antenna that is near the center of the array and has a minimum of flags. The array can be mapped with plotants:

# In CASA: phase only calibration
plotants(vis='G192-BP.ms')

although the plot is a bit crowded, a zoom in shows that ea05 sits close to the center and appears to be a good choice.

plotants plotter

plotcal G0 phase ant 0~15

plotcal G0 phase ant 16~26

plotcal K0 delay vs. antenna

plotcal B0 bandpass amp ant ea06 spw 0-31

plotcal B0 bandpass amp ant ea06 spw 32-63

First, we do a phase-only calibration solution on a narrow range of channels near the center of each spectral window on the bandpass calibrator 3C84 to flatten them with respect to time before solving for the bandpass. The range 60~68 should work. Pick a reference antenna near the center of the array -- ea05 is a reasonable choice (see above):

# In CASA: phase only calibration
gaincal(vis='G192-BP.ms', caltable='calG192.G0', \
        field='0', spw='*:60~68', \
        gaintype='G', refant='ea05', calmode='p', \
        solint='int', minsnr=3)

• refant='ea05' : Use ea05 as the reference antenna
• solint='int' : Do a per-integration solve (every 6 seconds, since we've time-averaged the data).
• minsnr=3 : Apply a minimum signal-to-noise cutoff. Solutions with less than this value will be flagged.
• gaintable is not set here as we have already applied pre-calibrations.

Plot the phase solutions (using full phase range, -180 to 180, instead of autorange):

# In CASA
plotcal(caltable='calG192.G0', xaxis='time', yaxis='phase', \
        iteration='antenna', plotrange=[-1,-1,-180,180])

The first panel is blanked as ea01 is completely flagged. Step through the antenna-based solutions, here they look good (and fairly flat over the scans).

NOTE: When you are done plotting and want to use the calibration table in another task (e.g., for subsequent calibration or viewing with plotms), use the Quit button on the GUI to dismiss the plotter and free-up the lock on the calibration table. You should see a message in your terminal window saying "Resetting plotcal" which means you are good to go!

If you want to make single-page, multipanel plots (like those shown to the right), particularly for a hardcopy (where it only shows the first page), you can do:

# In CASA
plotcal(caltable='calG192.G0', xaxis='time', yaxis='phase', \
        antenna='0~10,12~15', subplot=531, iteration='antenna', \
        plotrange=[-1,-1,-180,180], fontsize=8.0, \
        markersize=3.0, figfile='plotG192_plotcal_G0p1.png')
plotcal(caltable='calG192.G0', xaxis='time', yaxis='phase', \
        antenna='16~26', subplot=531, iteration='antenna', \
        plotrange=[-1,-1,-180,180], fontsize=8.0, \
        markersize=3.0, figfile='plotG192_plotcal_G0p2.png')

We can now solve for the residual delays that we saw in plotms when we plotted phase vs. frequency. This uses the gaintype='K' option in gaincal. Note that this currently does not do a "global fringe-fitting" solution for delays, but instead does a baseline-based delay solution for all baselines to the reference antenna, treating these as antenna-based delays. In most cases with high-enough S/N to get baseline-based delay solutions, this will suffice. We avoid the edge channels of each spectral window by selecting channels 5~122:

# In CASA: residual delays
gaincal(vis='G192_flagged_6s.ms', caltable='calG192.K0', \
        gaintable=['calG192.antpos', 'calG192.gaincurve', 'calG192.requantizer', \
                   'calG192.opacity', 'calG192.G0'], \
        field='3', spw='*:5~122', gaintype='K', \
        refant='ea05', solint='inf', minsnr=3)

Note that we have also pre-applied our initial phase table, calG192.G0. We can plot the delays, in nanoseconds, as a function of antenna index (you will get one for each spw and polarization):

# In CASA
plotcal(caltable='calG192.K0', xaxis='antenna', yaxis='delay')

The delays range from around -5 to 4 nanoseconds.

Now we solve for the antenna bandpasses using the previous tables:

# In CASA: antenna bandpasses
bandpass(vis='G192_flagged_6s.ms', caltable='calG192.B0', \
         gaintable=['calG192.antpos', 'calG192.gaincurve', 'calG192.requantizer', \
                    'calG192.opacity', 'calG192.G0', 'calG192.K0'], \
         field='3', refant='ea05', solnorm=False, \
         bandtype='B', solint='inf')

WARNING: You must set solnorm=False here or later on you will find some offsets among spws due to the way the amplitude scaling adjusts weights internally during solving.

plotcal B0 bandpass phase ant ea06 spw 0-31

plotcal B0 bandpass phase ant ea06 spw 32-63

You will see in the terminal some reports of solutions failing due to "Insufficient unflagged antennas" -- note that these are for the channels we flagged earlier.

This is the first amplitude-scaling calibration that we do, so it is important to have used the calG192.gaincurve caltable (or set gaincurve=True) as well as the calG192.opacity caltable (or set opacity appropriately).

Plot the resulting bandpasses in amplitude and phase:

# In CASA
plotcal(caltable='calG192.B0', xaxis='freq', yaxis='amp', \
        spw='0~31', iteration='antenna')
#
plotcal(caltable='calG192.B0', xaxis='freq', yaxis='amp', \
        spw='32~63', iteration='antenna')
#
plotcal(caltable='calG192.B0', xaxis='freq', yaxis='phase', \
        iteration='antenna', spw='0~31', \
        plotrange=[-1,-1,-180,180])
#
plotcal(caltable='calG192.B0', xaxis='freq', yaxis='phase', \
        iteration='antenna', spw='32~63', \
        plotrange=[-1,-1,-180,180])

In the bandpass phases you no longer see the residual antenna delays (just residual spw phase offsets from the delay solution registration), but there are some band edge effects apparent.

Bootstrapping the bandpass calibrator spectrum

Unfortunately, our flux density calibrator was not bright enough at Ka-band to use as the bandpass calibration source. Since there is no a priori spectral information for our chosen bandpass calibrator, 3C84, we need to bootstrap to find its spectral index, then recalibrate with this information in order to avoid folding the intrinsic spectral shape of 3C84 into our calibration.

First, we use the initial round of bandpass calibration to create gain solutions for the flux and bandpass calibrators:

# In CASA: flux and bandpass calibrators gain
gaincal(vis='G192_flagged_6s.ms', caltable='calG192.G1', field='0,3', \
        gaintable=['calG192.antpos', 'calG192.gaincurve', 'calG192.requantizer', \
                   'calG192.opacity', 'calG192.K0', \
                   'calG192.B0'], \
        gaintype='G', refant='ea05', calmode='ap', solint='30s', minsnr=3)

Now let's have a look at the phase and amplitude solutions, iterating over antenna. We will look at the flux calibrator (3C147) and bandpass calibrator (3C84) individually since they're widely separated in time:

# In CASA
plotcal(caltable='calG192.G1', xaxis='time', yaxis='amp', \
        field='0', iteration='antenna')
#
plotcal(caltable='calG192.G1', xaxis='time', yaxis='amp', \
        field='3', iteration='antenna')
#
plotcal(caltable='calG192.G1', xaxis='time', yaxis='phase', \
        iteration='antenna', plotrange=[-1,-1,-180,180], \
        field='0')
#
plotcal(caltable='calG192.G1', xaxis='time', yaxis='phase', \
        iteration='antenna', plotrange=[-1,-1,-180,180], \
        field='3')

The solutions all look reasonable and relatively constant with time.

Now that we have gain solutions for the flux and bandpass calibrators, we can use fluxscale to scale the gain amplitudes of the bandpass calibrator:

# In CASA: bandpass calibrator gain amplitudes scaling
flux1 = fluxscale(vis='G192_flagged_6s.ms', caltable='calG192.G1', \
                  fluxtable='calG192.F1', reference='0', \
                  transfer='3', listfile='3C84.fluxinfo', fitorder=1)

• flux1 = fluxscale(...): by providing a variable flux1, we allow fluxscale to use this for the output Python dictionary it returns with lots of information about the flux scaling. You can inspect the output dictionary flux1 by typing "print flux1" at the CASA command line.
• fluxtable='calG192.F1': this is the output scaled gain table. Since we are only using this to find the spectral index of 3C84, we won't be using this table.
• listfile='3C84.fluxinfo': an output file that contains the derived flux values and fit information.
• fitorder=1: only find a spectral index, ignoring curvature in the spectrum.

The last line in the file (and displayed in the logger) shows:

Fitted spectrum for 3c84-J0319+413 with fitorder=1: Flux density = 31.454 +/- 0.0310638 (freq=32.5128 GHz) spidx=-0.493668 +/- 0.00820698

plotms of model amp vs freq for 3C84

3C84 flux values returned by fluxscale

Using the information in the returned flux dictionary, we can plot the derived spectrum:

# In CASA
freq = flux1['freq'] / 1e9
spw_list = range(0,64)
spw_str = []
for i in spw_list:
   thisspw = str(i)
   spw_str.append(thisspw)

bootstrapped_fluxes = []
for j in spw_str:
    thisflux = flux1['3'][j]['fluxd'][0]
    if thisflux ==None:
        continue
    else:
        bootstrapped_fluxes.append(thisflux)

pl.clf()
pl.plot(freq, bootstrapped_fluxes, 'bo')
pl.xlabel('Frequency (GHz)')
pl.ylabel('Flux Density (Jy)')
pl.title('3C84')
pl.show()

Note the bump around 37 GHz -- what is this? We will not be able to account for it with the simple spectral index model, but still, ours is a good first approximation.

We can use the model from fluxscale to fill the MODEL column with 3C84's spectral information using setjy:

# In CASA: spectral information
setjy(vis='G192_flagged_6s.ms', field='3', scalebychan=True, \
      standard = 'manual', fluxdensity=[29.8756, 0, 0, 0], spix=-0.598929, \
      reffreq='32.4488GHz')

Checking with plotms that the data have been appropriately filled:

# In CASA
plotms(vis='G192_flagged_6s.ms', field='3', antenna='ea05&ea02', \
       xaxis='freq', yaxis='amp', ydatacolumn='model')

plotcal B0 bootstrapped bandpass amp ant ea06 spw 0-31

plotcal B0 bootstrapped bandpass amp ant ea06 spw 32-63

plotcal B0 bootstrapped bandpass phase ant ea06 spw 0-31

plotcal B0 bootstrapped bandpass phase ant ea06 spw 32-63

Finally, we redo the previous calibration using this new model information. Although the commands are the same as what we issued earlier, keep in mind that the model values for the bandpass calibrator have changed, and therefore the results of these calibration calculations will differ:

# In CASA: phase only recalibration
gaincal(vis='G192_flagged_6s.ms', caltable='calG192.G0.b', \
        field='3', spw='*:60~68', \
        gaintable=['calG192.antpos', 'calG192.gaincurve', \
                   'calG192.requantizer', 'calG192.opacity'], \
        gaintype='G', refant='ea05', calmode='p', \
        solint='int', minsnr=3) 
# In CASA: residual delays recalibration
gaincal(vis='G192_flagged_6s.ms', caltable='calG192.K0.b', \
        gaintable=['calG192.antpos', 'calG192.gaincurve', 'calG192.requantizer', \
                  'calG192.opacity', 'calG192.G0.b'], \
        field='3', spw='*:5~122', gaintype='K', \
        refant='ea05', solint='inf', minsnr=3)
# In CASA: antenna bandpasses recalibration
bandpass(vis='G192_flagged_6s.ms', caltable='calG192.B0.b', \
         gaintable=['calG192.antpos', 'calG192.gaincurve', 'calG192.requantizer', \
                    'calG192.opacity', 'calG192.G0.b', 'calG192.K0.b'], \
         field='3', refant='ea05', solnorm=False, \
         bandtype='B', solint='inf')

It's a good idea to inspect these solutions as well:

# In CASA
plotcal(caltable='calG192.B0.b', xaxis='freq', yaxis='amp', \
        spw='0~31', iteration='antenna')
#
plotcal(caltable='calG192.B0.b', xaxis='freq', yaxis='amp', \
        spw='32~63', iteration='antenna')
#
plotcal(caltable='calG192.B0.b', xaxis='freq', yaxis='phase', \
        iteration='antenna', spw='0~31', \
        plotrange=[-1,-1,-180,180])
#
plotcal(caltable='calG192.B0.b', xaxis='freq', yaxis='phase', \
        iteration='antenna', spw='32~63', \
        plotrange=[-1,-1,-180,180])

They look virtually unchanged from the previous solutions, with the exception that the amplitude scaling is corrected for the spectrum of 3C84. Now that we have the final version of our bandpass calibration, we can proceed to the full calibration of the dataset.