ADC/CDS Standard Document for Catalog:/journal_tables/ApJS/128/17/
ADC/CDS Standard Document for Catalog:| 1. Use the ADC Data Viewer Suite to visualize the data. |
|
| 2. Get the data files via anonymous FTP. (See Note.) |
|
J/ApJS/128/17 VLBA obs. of radio reference frame sources. III. (Fey+, 2000)
================================================================================
VLBA observations of radio reference frame sources.
III. Astrometric suitability of an additional 225 sources.
Fey A.L., Charlot P.
<Astrophys. J. Suppl. Ser. 128, 17 (2000)>
=2000ApJS..128...17F (SIMBAD/NED BibCode)
================================================================================
ADC_Keywords: Galaxies, radio ; QSOs ; Morphology
Keywords: astrometry - quasars: general - radio continuum: galaxies - surveys
Abstract:
We present simultaneous dual-frequency Very Long Baseline Array 2 and
8 GHz observations of 225 of the 560 extragalactic sources for which
positions were reported by Johnston and coworkers and which are now
part of the International Celestial Reference Frame. These
observations represent the third and final in a series of observations
intended to obtain single-epoch images of the entire set of sources
presented by Johnston and coworkers (1995, Cat. <J/AJ/110/880>) and,
together with previously reported observations, bring the total number
of sources observed to 389. As with previous papers in this series, we
use these data to quantify the magnitude of the expected effect of
intrinsic source structure on astrometric bandwidth synthesis Very
Long Baseline Interferometry observations and to calculate a source
"structure index" for the observed sources. The structure index can be
used as an estimate of the astrometric quality of the sources. Based
on this indicator, correlations between the observed radio structure
and the astrometric position accuracy and stability of the sources
have been found. These correlations indicate that the more extended
sources have larger position uncertainties and are less positionally
stable than the more compact sources.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 55 460 Parameters of naturally weighted images
--------------------------------------------------------------------------------
See also:
J/AJ/110/880 : Radio reference frame (Johnston+ 1995)
I/251 : VLBI International Celestial Reference Frame (ICRF) (Ma+, 1997)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- IERS Source name (IERS BHHMM+DDd in Simbad)
10- 13 F4.2 GHz nu Fiducial frequency (2.32 or 8.55GHz)
15- 18 F4.1 mas a Beam major axis (1)
20- 23 F4.1 mas b Beam minor axis (1)
25- 27 I3 deg phi Beam major axis position angle (1)
29- 32 F4.2 Jy SPeak Peak flux density at frequency nu
34- 37 F4.1 mJy rms rms of the residuals of the final hybrid image
39- 55 A17 mJy Cont Contour levels (2)
--------------------------------------------------------------------------------
Note (1): The restoring beam is an elliptical Gaussian with FWHM major axis
a and minor axis b, with major axis in position angle phi
(measured north through east).
Note (2): Contour levels are represented by the geometric series 1,..., 2^n^;
e.g., for n = 5 the contour levels would be +/-1, 2, 4, 8, 16, 32
--------------------------------------------------------------------------------
History: From ApJS electronic version
References:
Fey et al., Paper I 1996ApJS..105..299F
Fey & Charlot, Paper II 1997ApJS..111...95F
================================================================================
(End) James Marcout, Patricia Bauer [CDS] 18-Sep-2000