4.1. Key to the VLA Calibrator Manual

   The following table lists all of the sources which have been found to
be suitable calibrators for the VLA.  The quality of some calibrators
varies with frequency and configuration and the table includes comments
pertaining to this.  Several examples from the table are given below:

IAU NAME EQUINOX  PC RA(hh,mm,ss)    DEC(ddd,mm,ss)   POS.REF ALT.NAME
0003-174   J2000  T 00h03m21.9969s   -17d27'11.781"
0000-177   B1950  T 00h00m48.4200s   -17d43'54.000"
BAND        A B C D    FLUX(Jy)    UVMIN(kL)  UVMAX(kL)
 90cm    P  X S S S          7                        7
 20cm    L  X X X S        2.2                        7
0005+383   J2000  A 00h05m57.1755s    38d20'15.169"   Oct96   CJ2
0003+380   B1950  A 00h03m22.3357s    38d03'33.430"
BAND        A B C D    FLUX(Jy)    UVMIN(kL)  UVMAX(kL)
 20cm    L  X X X X       0.40
  6cm    C  P P P P       0.80                        visplot
3.7cm    X  P P P P       1.1
0038-213   J2000  C 00h38m29.9524s   -21d20'04.027''
0036-216   B1950  C 00h36m00.4390s   -21d36'33.100''
BAND        A B C D    FLUX(Jy)    UVMIN(kL)  UVMAX(kL)
 20cm    L  ? ? X X       0.78           10
  6cm    C  S S S S       0.34                      200
3.7cm    X  X S S S       0.22                      200

0714+146   J2000  T 07h14m04.6352s    14d36'20.629''   3C175.1
0711+146   B1950  T 07h11m14.3000s    14d41'33.000''
BAND        A B C D    FLUX(Jy)    UVMIN(kL)  UVMAX(kL)
 90cm    P  X S S X          6            1           4
 20cm    L  X X X S       1.90                        4
1733-130   J2000  A 17h33m02.7058s   -13d04'49.546''
1730-130   B1950  A 17h30m13.5352s   -13d02'45.837''
BAND        A B C D    FLUX(Jy)    UVMIN(kL)  UVMAX(kL)
 20cm    L  S X X P       5.20           40           3
  6cm    C  P P P P       5.00
3.7cm    X  P P S S       5.80           15
  2cm    U  P P P P       3.70
1759+237   J2000  C 17h59m00.3527s    23d43'46.974''
1756+237   B1950  C 17h56m55.9320s    23d43'55.800''
BAND        A B C D    FLUX(Jy)    UVMIN(kL)  UVMAX(kL)
 20cm    L  S S S X       0.70            6          90
  6cm    C  X S S S       1.00                       90
3.7cm    X  S S S S       0.55
  2cm    U  ? ? ? ?       0.00


Line 1:          Source IAU name at equinox (2000).  Use
                 of this name in OBSERVE fetches RA
                 and DEC at equinox 2000.
            PC = Position Code for coordinate accuracy.
                 Position change reference.
           Oct96 Adoption of Eubanks 1995-1 positions from USNO
                 geodetic observations.
           Nov96 G.Taylor A configuration 3.7cm VLA
           Dec96 C.Carilli A configuration 0.7cm VLA
           Jan97 G.Taylor B configuration 3.7cm VLA
           Feb97 G.Taylor B configuration 3.7cm VLA
           Aug99 M.Goss A config 3.7cm VLA confirmed by 6cm VLA
           May00 J.Wrobel A configuration 3.7cm and 6cm VLA
           Dec00 E.Fomalont, VSOP pre-launch survey, 5 GHz geodetic
           Aug01 VLBA Calibrator Survey astrometric positions
                 Alternate name, if any.  The alternate name
                 is NOT recognized by OBSERVE.  An entry of
                 CJ2 indicates that the source is included in
                 the Second Caltech-Jodrell Bank VLBI survey,
                 and JVAS is the Jodrell Bank VLA Astrometric Survey.

Line 2:          Source IAU name at equinox (1950).  Use
                 of this name in OBSERVE fetches RA
                 and DEC at equinox 1950.  Secondary 
                 alternate name -- not recognized by OBSERVE.

Position Codes are:
   A = positional accuracy <0.002  arcseconds
   B = positional accuracy  0.002 - 0.01  arcseconds
   C = positional accuracy  0.01 - 0.15  arcseconds
   T = positional accuracy >0.15  arcseconds

   Notes:   1. For the most accuracy J2000 is strongly preferred (see 
            section 3.2.)
            2. Errors in declination increase in the south, except for A
            and B calibrators.


   Col 1 & 2:    Band and Band code.  For 1.3cm use 2cm entry.
   Col 3-6:      Calibrator quality in the A, B, C and D configuration
                 determined using a 50 MHz observing bandwidth:

                 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 = The approximate flux density of the source.
                 Use only as an indicator of the source strength.

   Col 8 & 9:    CALIB restrictions.  These are suggested UVLIMITS in
                 thousands of wavelengths to use in CALIB to avoid
                 data which are contaminated by structure.  A UVMIN 
                 (Col. 8) generally means the source is confused at 
                 short spacings.  A UVMAX (Col. 9) generally means the 
                 source is resolved at long spacings.  Setting WTUV=0.1
                 in CALIB will help to ensure stability.
Hypertext Links:  If viewing the calibrator manual on the world wide
                 web at http://www.aoc.nrao.edu/~gtaylor/calib.html
                 with Netscape or an equivalent browser, links
                 to some maps and visibility plots are provided.  A 
                 postscript viewer is needed to view the plots.

Particular comments on entries in the calibrator manual:

1. Although '?' appears in the table for 0038-213 it is likely that
   the source is a fine calibrator at 20cm in the A and B
   configurations since it is unresolved at 6 and 3.6cm at similar
   resolutions.  It is listed with a '?' because we have not
   confirmed its suitability.  Many '?' entries can be interpreted in
   this way.

2. The X at 20cm C and D configurations for 0038-213 and the UVMIN
   means that the source is confused at short spacings at 20cm.  The
   source could be used, but gain quality would be poorer.

3. The source 0714+146 is only a calibrator at 20cm in the D
   configuration and in B and C configurations at 90cm.  Many
   similarly extended sources are included in the listings.  Most are
   fairly strong and can be used as bandpass calibrators at 20cm.

4. The inaccurate position (PC-T) of 0714+146 is not a restriction
   for 20cm D configuration observing.

5. Note the apparent conflict in UVLIMITS for 1733-130 at 20cm.  This
   conflict is resolved by noting that two different ranges will
   allow a valid CALIB solution; the first, valid for the D array, is
   0 to 3 k wavelengths; the second, valid for the A array, is 40 k
   wavelengths to the longest baseline (approximately 180 k

6. The 2cm listing for 1759+237 has zero flux density and '?' for
   quality, indicating it has not been observed.  Because the source
   shows a flat spectrum, it is likely to be a good calibrator at

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