J/AJ/136/580 Sixth VLBA calibrator survey: VCS6 (Petrov+, 2008)
The sixth VLBA calibrator survey: VCS6.
Petrov L., Kovalev Y.Y., Fomalont E.B., Gordon D.
<Astron. J., 136, 580-585 (2008)>
=2008AJ....136..580P 2008AJ....136..580P
ADC_Keywords: Surveys ; Radio sources
Keywords: astrometry - catalogs - radio continuum: galaxies - surveys
Abstract:
This paper presents the sixth part of the Very Long Baseline Array
(VLBA) Calibrator Survey. It contains the positions and maps of 264
sources of which 169 were not previously observed with very long
baseline interferometry. This survey, based on two 24h VLBA observing
sessions, was focused on (1) improving positions of 95 sources from
previous VLBA Calibrator Surveys that were observed either with very
large a priori position errors or were observed not long enough to get
reliable positions and (2) observing remaining new flat-spectrum
sources with predicted correlated flux density in the range 100-200mJy
that were not observed in previous surveys. Source positions were
derived from astrometric analysis of group delays determined at the
2.3 and 8.6GHz frequency bands using the Calc/Solve software package.
The VCS6 catalog of source positions, plots of correlated flux density
versus projected baseline length, contour plots and fits files of
naturally weighted CLEAN images, as well as calibrated visibility
function files, are available on the Web at
http://vlbi.gsfc.nasa.gov/vcs6.
Description:
Observations were performed in two 24h sessions with the VLBA on 2006
December 18 and 2007 January 11. The target sources were observed in a
sequence designed to minimize loss of time from antenna slewing. In
addition to these objects, observations of 3-4 strong sources from a
list of 62 tropospheric calibrators were made every 1-1.5h during the
sessions.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 119 264 The VCS6 catalog
table5.dat 49 21 Sources not detected in VCS6 VLBA observations
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See also:
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/AJ/126/2562 : Second VLBA calibrator survey: VCS2 (Fomalont+, 2003)
J/AJ/129/1163 : Third VLBA calibrator survey: VCS3 (Petrov+, 2005)
J/AJ/131/1872 : Fourth VLBA calibrator survey: VCS4 (Petrov+, 2006)
J/AJ/133/1236 : Fifth VLBA calibrator survey: VCS5 (Kovalev+, 2007)
J/AJ/136/580 : Sixth VLBA calibrator survey: VCS6 (Petrov+, 2008)
http://vlbi.gsfc.nasa.gov/vcs6 : VCS6 Home Page
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1 A1 --- Cat [CNU] Category (1)
4- 11 A8 --- IVS The IVS name (HHMM-DDd, B1950)
13- 22 A10 --- IAU The IAU name (JHHMM-DDMM, J2000.0)
25- 26 I2 h RAh Hour of Right Ascension (J2000)
28- 29 I2 min RAm Minute of Right Ascension (J2000)
31- 39 F9.6 s RAs Second of Right Ascension (J2000)
41 A1 --- DE- Sign of the Declination (J2000)
42- 43 I2 deg DEd Degree of Declination (J2000)
45- 46 I2 arcmin DEm Arcminute of Declination (J2000)
48- 55 F8.5 arcsec DEs Arcsecond of Declination (J2000)
58- 63 F6.2 mas e_RAs Inflated error in Right Ascension
65- 70 F6.2 mas e_DEs Inflated error in Declination
73- 78 F6.3 --- Corr Correlation between Right Ascension and
Declination
80- 85 I6 --- Nobs Number of observations used
88 A1 --- l_S(X) Limit flag on S(X)
89- 92 F4.2 Jy S(X) ?=- X-band (8.6GHz) total flux density
integrated over entire map
94 A1 --- l_S(X)u Limit flag on S(X)u
95- 98 F4.2 Jy S(X)u ?=- X-band (8.6GHz) unresolved flux density at
longest VLBA baselines
101 A1 --- l_S(S) Limit flag on S(S)
102-105 F4.2 Jy S(S) ?=- S-band (2.3GHz) total flux density
integrated over entire map
107 A1 --- l_S(S)u Limit flag on S(S)u
108-111 F4.2 Jy S(S)u ?=- S-band (2.3GHz) unresolved flux density at
longest VLBA baselines
114-116 A3 --- Band [X/S ] Band used for position estimation:
X(8.6GHz), S(2.3GHz), X/S(both)
119 A1 --- list Input list name (2)
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Note (1): Category code as follows:
C = calibrator, i.e. the semi-major axis of the inflated error
ellipse is less than 5mas and more than 8 good pairs of X/S
group delay measurements are available
N = non-calibrator with reliable coordinates, i.e. does not fit the
condition to be considered as calibrator, but has more than 8
good group delay measurements at X or S band
U = non-calibrator with unreliable coordinates, i.e. does not fit the
condition to be considered as calibrator, has less than 8
detections at any band, and therefore, there is a risk that
group delay ambiguities were resolved incorrectly
Note (2): Input list name code as follows:
a = 27 known sources which previously were observed with a priori
errors >30"
r = 68 sources observed in VCS1-2 with 64Mb/s rate, which yielded 1-9 obs.
v = 139 leftovers from the VCS5 list
i = 30 IDV sources with flux density average >130mJy
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- IVS The IVS name (HHMM-DDd,B1950)
11- 20 A10 --- IAU The IAU name (JHHMM-DDMM, J2000)
24- 25 I2 h RAh Hour of Right ascension (J2000) (1)
27- 28 I2 min RAm Minute of Right ascension (J2000) (1)
30- 34 F5.2 s RAs Second of Right ascension (J2000) (1)
39 A1 --- DE- Sign of the Declination (J2000) (1)
40- 41 I2 deg DEd Degree of Declination (J2000) (1)
43- 44 I2 arcmin DEm Arcminute of Declination (J2000) (1)
46- 49 F4.1 arcsec DEs Arcsecond of Declination (J2000) (1)
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Note (1): The J2000 source positions are taken from the NVSS survey
(Condon et al., 1998, Cat. VIII/65), they were used for VCS6
VLBA observing and correlation.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 12-Feb-2011