WBR Step 2. Looking at the Contents of Your Data

So you've loaded in your data and you have a nice CH 0 file and a LINE file. Now what? You probably want to know what frequency your data was taken at, how many channels it has, what sources were observed, etc. See below for how to extract this information from the AIPS maze.


First, let's look at the header of one of these data files. If you type "uc", you will have a list of all the uv files. The first column lists the catalog number of each data file. Like this:

>uc 
AIPS 1: Catalog on disk  1
AIPS 1:  Cat Usid Mapname      Class   Seq  Pt     Last access      Stat
AIPS 1:    1   53 MULTI4.8    .CH0   .    1 UV 15-JUN-2006 14:16:14
AIPS 1:    2   53 MULTI4.8    .LINE  .    1 UV 23-MAR-2007 00:32:51

If I want to access and screw around with the CH0 data set, I would type 'getn 1', because '1' is the CAT number for this data set. Then, to view the header, just type 'imh'.

#getn 1
AIPS 1: Got(1)   disk= 1  user=  53   type=UV   MULTI4.8.CH0.1
>imh
AIPS 1: Image=MULTI     (UV)         Filename=MULTI4.8    .CH0   .   1
AIPS 1: Telescope=VLA                Receiver=VLA
AIPS 1: Observer=AW649               User #=   53
AIPS 1: Observ. date=15-MAY-2005     Map date=02-DEC-2005
AIPS 1: # visibilities   1009820     Sort order  TB
AIPS 1: Rand axes: UU-L-SIN  VV-L-SIN  WW-L-SIN  BASELINE  TIME1
AIPS 1:            SOURCE  FREQSEL  WEIGHT  SCALE
AIPS 1: ----------------------------------------------------------------
AIPS 1: Type    Pixels   Coord value     at Pixel     Coord incr   Rotat
AIPS 1: COMPLEX      1   1.0000000E+00       1.00  1.0000000E+00     .00
AIPS 1: FREQ         1   4.8851000E+09       1.00  1.5625000E+07     .00
AIPS 1: STOKES       2  -1.0000000E+00       1.00 -1.0000000E+00     .00
AIPS 1: IF           2   1.0000000E+00       1.00  1.0000000E+00     .00
AIPS 1: RA           1    00 00 0 .000       1.00       3600.000     .00
AIPS 1: DEC          1    00 00 0 .000       1.00       3600.000     .00
AIPS 1: ----------------------------------------------------------------
AIPS 1: Coordinate equinox 2000.00
AIPS 1: Maximum version number of extension files of type HI is   1
AIPS 1: Maximum version number of extension files of type AN is   1
AIPS 1: Maximum version number of extension files of type NX is   1
AIPS 1: Maximum version number of extension files of type SU is   1
AIPS 1: Maximum version number of extension files of type FQ is   1
AIPS 1: Maximum version number of extension files of type CL is   1
AIPS 1: Maximum version number of extension files of type TY is   1
AIPS 1: Maximum version number of extension files of type WX is   1
AIPS 1: Maximum version number of extension files of type OF is   1
AIPS 1: Keyword = 'OBSCHANS'  value =            8
AIPS 1: Keyword = 'CORRMODE'  value = '4       '
AIPS 1: Keyword = 'SELCHANS'  value =            7
AIPS 1: Keyword = 'VLAIFS  '  value = 'ABCD    '

This header tells me all sorts of useful things, like that my data was taken at 4.8 GHz, and that there are 2 polarizations ('STOKES') and 2 IFs (What is an IF? Basically, if you observe at 2 IFs, it's like observing at 2 slightly different frequencies. So, for example, if I was observing the OH molecular lines at 1665 and 1667 MHz, I could put one IF down on each line. In continuum, you get twice the bandwidth if you have 2 IFs!). It also tells me that there is only 1 channel in this file (FREQ 1), which there should be because it's CH0! However, it does tell me further down that the observation was set up to have 7 channels ('SELCHANS' value = 7), so I can expect that in the LINE data.

Next up, you can see what sources were observed and when if you run LISTR. The important parameter to set here is:
OPTYPE = 'scan'
Also, you probably want LISTR to write out to a file, so set
DOCRT = -1
OUTPRINT = 'filename'
Most everything else can be left as default for now.

AIPS 1: LISTR:  Task to print UV data and calibration tables.
AIPS 1: Adverbs     Values                 Comments
AIPS 1: ----------------------------------------------------------------
AIPS 1: USERID        0                    User number.
AIPS 1: INNAME     'MULTI4.8'              UV data (name).
AIPS 1: INCLASS    'CH0'                   UV data (class).
AIPS 1: INSEQ         1                    UV data (seq. #).  0 => high
AIPS 1: INDISK        1                    Disk unit #.       0 => any
AIPS 1: OPTYPE     'SCAN'                  List type:
AIPS 1:                                     'MATX','LIST','GAIN','SCAN'
AIPS 1: INEXT      'CL'                    CL, SN or TY table for 'GAIN'
AIPS 1: INVER         0                    CL, Sn or TY table version
AIPS 1: SOURCES    *all ' '                Source list
AIPS 1: CALCODE    ' '                     Calibrator code '    '=>all
AIPS 1: TIMERANG   *all 0                  Time range to list
AIPS 1: STOKES     'HALF'                  Stokes type to list.
AIPS 1: SELBAND      -1                    Bandwidth to select (kHz)
AIPS 1: SELFREQ      -1                    Frequency to select (MHz)
AIPS 1: FREQID        1                    Freq. ID to select.
AIPS 1:                                    None selected => 1.
AIPS 1: BIF           1                    Lowest IF number 0=1
AIPS 1: EIF           2                    Highest IF number
AIPS 1: BCHAN         1                    Low channel number 0=>1
AIPS 1: ECHAN         0                    High channel number
AIPS 1: ANTENNAS   *all 0                  Antennas to list
AIPS 1: BASELINE   *all 0                  Baselines with ANTENNAS
AIPS 1: UVRANGE       0           0        UV range in kilolambda
AIPS 1: SUBARRAY      0                    Subarray, 0=>1
AIPS 1:                                    Cal. info for input:
AIPS 1: DOCALIB      -1                    If >0 calibrate data
AIPS 1:                                    = 2 calibrate weights
AIPS 1: GAINUSE       0                    CAL (CL or SN) table to apply
AIPS 1: DOPOL        -1                    If >0 correct polarization.
AIPS 1: BLVER        -1                    BL table to apply.
AIPS 1: FLAGVER       0                    Flag table version
AIPS 1: DOBAND       -1                    If >0 apply bandpass cal.
AIPS 1:                                    Method used depends on value
AIPS 1:                                    of DOBAND (see HELP file).
AIPS 1: BPVER        -1                    Bandpass table version
AIPS 1: SMOOTH     *all 0                  Smoothing function. See
AIPS 1:                                    HELP SMOOTH for details.
AIPS 1: DPARM         5           1        Control info:
AIPS 1:            *rest 0                 (1) 0=amp, 1=phase, 2=rms
AIPS 1:                                        3=amp+rms, 4=phase+rms
AIPS 1:                                        5=amp+phase, 6=delay,
AIPS 1:                                        7=rate, 8=SNR, 9=par. ang
AIPS 1:                                        10 = Tsys, 11=elev,
AIPS 1:                                        12 = multiband delay
AIPS 1:                                        13 = Tant  14 = weights
AIPS 1:                                        N.B. Options 3 and 4 only
AIPS 1:                                        valid for OPTYPE = 'MATX'
AIPS 1:                                    (2) 0=vec avg, 1=scalar
AIPS 1:                                    (3) No. col (4-10) def=4.
AIPS 1:                                    (4) avg. time min (MATX,LIST)
AIPS 1:                                        *** significant
AIPS 1:                                    (5) Type of gain listings:
AIPS 1:                                        0 => all with same scale
AIPS 1:                                        like DEC-10 listings;
AIPS 1:                                        1 => scan/source info at
AIPS 1:                                        source/scan boundaries.
AIPS 1:                                    (6) Matrix scaling control:
AIPS 1:                                        0 => plot amp & rms
AIPS 1:                                        matrices with same scale;
AIPS 1:                                        1 => self-scale each
AIPS 1:                                        separately.
AIPS 1:                                    (7) > 0 self-scale phase
AIPS 1:                                        displays, else degrees.
AIPS 1: DOACOR       -1                    > 0 include autocorrelations
AIPS 1: FACTOR        0                    When DPARM(5)=0 Multiply
AIPS 1:                                    gain listings by FACTOR,
AIPS 1:                                    0=> use scale factor from
AIPS 1:                                    first record printed.
AIPS 1: DOCRT        -1                    > 0 -> use the terminal,
AIPS 1:                                    else use the line printer
AIPS 1:                                    > 72 => terminal width
AIPS 1: OUTPRINT   'SCANS'
AIPS 1:                                    Printer disk file to save
AIPS 1: BADDISK    *all 0                  Disk to avoid for scratch.

Now, if you look at the file 'SCANS', you should see a list of at least 3 sources. One source will be your flux calibrator; it is usually only observed once or twice per night. Another source will be your phase calibrator; it will be observed approximately every 30 minutes. And finally, there will be your target source(s)!

Look up your calibrators in the VLA Calibrator Manual . Copy to some convenient file or piece of paper the flux of your calibrators at your observing frequency, and the uvmin and uvmax.