VLA Calibrator Manual

The VLA has been used to observe sources all over the sky within the range of RA dn DEC and a set of sources have been identified as suitable calibrators for VLA which are listed in the VLA calibrator manual. The quality of some calibrators varies with frequency and configuration and the manual includes comments pertaining to this.
(Ref : http://www.vla.nrao.edu/astro/calib/manual/index.shtml)

Herewith we are giving an example of a calibrator source listed in the VLA calibrator manual. We also describe the table format of the manual.

0534+194   J2000  C 05h34m44.5183s    19d27'21.378"
0531+194   B1950  C 05h31m47.3570s    19d25'24.750"
-----------------------------------------------------
BAND        A B C D    FLUX(Jy)    UVMIN(kL)  UVMAX(kL)
=====================================================
 90cm    P  S S S X         15            2
 20cm    L  X S P P       6.80                       50
  6cm    C  X X S P       2.50                       50
  2cm    U  X X X S        0.9                       50
0.7cm    Q  X X X X        0.0

The description of table format:

• The first two rows give the source name in J2000 (2000 epoch) or B1950 (1950 epoch), the position codes (column 3 of first two rows) and the source co-ordinates in RA (hh,mm,ss) & DEC(dd,mm,ss).

  The position codes are:

     A = positional accuracy <0.002  arc-seconds
     B = positional accuracy  0.002 to 0.01  arc-seconds
     C = positional accuracy  0.01 to 0.15  arc-seconds
     T = positional accuracy >0.15  arc-seconds
  

• Col 1 & 2: Below the source names in the Table, Col 1 gives the wavelength & Col. 2 gives frequency band (see table 3.2) for which the source has been identified as a calibrator.

• Col 3 to 6: Calibrator quality for each of the configurations A, B, C & D (for maximum antenna distance for each configurations, see table 3.1) determined using an observing bandwidth of 50 MHz.

  Typically, the calibrator qualities are listed as:

  	P = <3% amplitude closure errors expected
  	S = 3-10% closure errors expected
  	W = 10-?% closure errors expected.  Suitable for calibration of phases only. 
  	C = Confused
  	X = Do not use.  Too much resolution or too weak
  	? = Structure unknown
  

• Col 7: Flux density; the approximate flux density of the source in Jy.

• Col 8 & 9: The suggested UV-limits in thousands of wavelengths (kL) to use while calibration in order to avoid data which are contaminated by structure. A UVMIN (Col. 8) generally means the source is confused at short spacings/baselines and a UVMAX (Col. 9) generally means the source is resolved at long spacings/baselines.