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
TABLE HEADER
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.
TABLE FORMAT
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
wavelengths).
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
2cm.
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