J/AJ/130/2529 8.4GHz VLBI observations of Southern ICRF sources (Ojha+, 2005)
VLBI observations of southern hemisphere ICRF sources.
II. Astrometric suitability based on intrinsic structure.
Ojha R., Fey A.L., Charlot P., Jauncey D.L., Johnston K.J., Reynolds J.E.,
Tzioumis A.K., Quick J.F.H., Nicolson G.D., Ellingsen S.P., McCulloch P.M.,
Koyama Y.
<Astron. J., 130, 2529-2540 (2005)>
=2005AJ....130.2529O 2005AJ....130.2529O (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; QSOs
Keywords: astrometry - galaxies: active - quasars: general -
radio continuum: galaxies - reference systems - surveys
Abstract:
We present 8.4GHz very long baseline interferometry (VLBI)
observations of 48 southern hemisphere extragalactic sources from the
International Celestial Reference Frame. These are the second in a
series of observations intended to image all such sources in the
southern hemisphere at milliarcsecond resolution and bring the total
number of observed sources to 111. We use these data, together with
previously published data, to quantify the magnitude of the expected
effect of intrinsic source structure on astrometric bandwidth
synthesis VLBI observations by calculating a "structure index" for the
sources; the structure index yields an estimate of their astrometric
quality.
Description:
The observations reported in this paper were made using the five
telescopes that make up the Australian LBA, as well as telescopes in
South Africa, Hawaii, and Japan.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 40 85 Gaussian models
table4.dat 24 48 Physical characteristics of sources
table5.dat 40 122 Source structure index
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See also:
I/251 : VLBI International Celestial Reference Frame (ICRF) (Ma+, 1997)
J/AJ/127/3587 : VLBI ICRF. II (Fey+, 2004)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- PKS Source name
10 I1 --- Comp [1/3] Component number
12- 16 F5.3 Jy S [0.006/2.28] Total component flux density
18- 21 F4.1 mas Dist [0/75.9] Distance of component from core
23- 26 I4 deg theta [-167/131]? Orientation of component (1)
28- 31 F4.2 mas MajAxis [0/5.66] Length of major axis of component
33- 36 F4.2 --- b/a [0.36/1] Axial ratio (2)
38- 40 I3 deg phi [-67/26]? Orientation of major axis of
component (3)
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Note (1): With respect to the core component.
Note (2): Circular model components (b/a=1) were the default choice with
elliptical model components being used where circular model
components clearly did not provide a good fit.
Note (3): Measured north through east.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- PKS Source name
10- 11 A2 --- f_PKS [QG? ] QSO or Galaxy
13- 17 F5.3 --- z [0.003/3.8]? Redshift
19- 23 F5.2 mag mag [8.98/24]? Visual magnitude
24 A1 --- Band [B]Bandpass to which the magnitude applies (1)
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Note (1): For example, U, B, V, R, and I are for the standard Johnson and/or
Cousins magnitudes. If no letter is given, the filters are not
currently specified in NED. These magnitudes should be regarded as
indicative only.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- PKS Source name
10- 15 F6.1 ps tau-mean [0.1/1385.5] Mean structure delay correction
17- 22 F6.1 ps tau-rms [0.2/1667] RMS structure delay correction
24- 29 F6.1 ps tau-max [0.4/6458.7] Maximum structure delay correction
31- 36 F6.1 ps tau-median [0.1/1313] Median structure delay correction
38 I1 --- S-Index [1/4] Structure index (1)
40 A1 --- Epoch [A-E] Observational epoch (2)
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Note (1): Fey & Charlot (1997ApJS..111...95F 1997ApJS..111...95F) defined a source "structure index"
according to the median value of the structure delay corrections,
τmedian, separating the sources into four classes, as follows:
1 = 3ps≤τmedian< 3ps;
2 = 3ps≤τmedian<10ps;
3 = 10ps≤τmedian<30ps;
4 = 30ps≤τmedian<∞.
Note (2): Observational epoch, defined as follows:
A = 2002 July 16;
B = 2002 November 14;
C = 2003 June 20;
D = 2003 November 23;
E = 2004 April 18.
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History:
From electronic version of the journal
References:
Ojha et al., Paper I 2004AJ....127.3609O 2004AJ....127.3609O
(End) Greg Schwarz [AAS], Marianne Brouty [CDS] 05-May-2006