J/AJ/151/79 Radio fluxes of 195 ICRF2-Gaia transfer sources (Le Bail+, 2016)
IVS observation of ICRF2-Gaia transfer sources.
Le Bail K., Gipson J.M., Gordon D., MacMillan D.S., Behrend D.,
Thomas C.C., Bolotin S., Himwich W.E., Baver K.D., Corey B.E., Titus M.,
Bourda G., Charlot P., Collioud A.
<Astron. J., 151, 79 (2016)>
=2016AJ....151...79L 2016AJ....151...79L (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Radio sources ; Interferometry
Keywords: astrometry - catalogs - quasars: general - reference systems -
techniques: interferometric
Abstract:
The second realization of the International Celestial Reference Frame
(ICRF2), which is the current fundamental celestial reference frame
adopted by the International Astronomical Union, is based on Very Long
Baseline Interferometry (VLBI) data at radio frequencies in X band and
S band. The European Space Agency's Gaia mission, launched on 2013
December 19, started routine scientific operations in 2014 July. By
scanning the whole sky, it is expected to observe ∼500000 Quasi
Stellar Objects in the optical domain an average of 70 times each
during the five years of the mission. This means that, in the future,
two extragalactic celestial reference frames, at two different
frequency domains, will coexist. It will thus be important to align
them very accurately. In 2012, the Laboratoire d'Astrophysique de
Bordeaux (LAB) selected 195 sources from ICRF2 that will be observed
by Gaia and should be suitable for aligning the radio and optical
frames: they are called ICRF2-Gaia transfer sources. The LAB submitted
a proposal to the International VLBI Service (IVS) to regularly
observe these ICRF2-Gaia transfer sources at the same rate as Gaia
observes them in the optical realm, e.g., roughly once a month. We
describe our successful effort to implement such a program and report
on the results. Most observations of the ICRF2-Gaia transfer sources
now occur automatically as part of the IVS source monitoring program,
while a subset of 37 sources requires special attention. Beginning in
2013, we scheduled 25 VLBI sessions devoted in whole or in part to
measuring these 37 sources. Of the 195 sources, all but one have been
successfully observed in the 12 months prior to 2015 September 01. Of
the sources, 87 met their observing target of 12 successful sessions
per year. The position uncertainties of all of the ICRF2-Gaia transfer
sources have improved since the start of this observing program. For a
subset of 24 sources whose positions were very poorly known, the
uncertainty has decreased, on average, by a factor of four. This
observing program is successful because the two main goals were
reached for most of the 195 ICRF2-Gaia transfer sources: observing at
the requested target of 12 successful sessions per year and improving
the position uncertainties to better than 200µas for both R.A. and
decl. However, scheduling some of the transfer sources remains a
challenge because of network geometry and the weakness of the sources,
and this will be one focus of future sessions used in this ongoing
program.
Description:
The second realization of the International Celestial Reference Frame
(ICRF2) is based on Very Long Baseline Interferometry (VLBI) data at
radio frequencies in X band and S band. The European Space Agency's
Gaia mission, launched on 2013 December 19, started routine scientific
operations in 2014 July. By scanning the whole sky, it is expected to
observe ∼500000 Quasi Stellar Objects in the optical domain. This
means that, in the future, two extragalactic celestial reference
frames, at two different frequency domains, will coexist. It will thus
be important to align them very accurately.
In 2012, the Laboratoire d'Astrophysique de Bordeaux (LAB) selected
195 sources from ICRF2 that will be observed by Gaia and should be
suitable for aligning the radio and optical frames: they are called
ICRF2-Gaia transfer sources. The LAB submitted a proposal to the
International VLBI Service (IVS) to regularly observe these ICRF2-Gaia
transfer sources at the same rate as Gaia observes them in the optical
realm, e.g., roughly once a month.
Of the 195 sources, all but one have been successfully observed in the
12 months prior to 2015 September 01. Table1 lists the 195 ICRF2-Gaia
transfer sources.
Beginning in 2003 June, the Goddard VLBI group developed a program to
purposefully monitor when sources were observed and to increase the
observations of "under-observed" sources. In 2013 March, we added all
195 ICRF2-Gaia transfer sources to the IVS source monitoring program
with an observation target of 12 successful sessions per year.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 102 195 *Candidate ICRF2-Gaia transfer sources to align
the radio catalog and the Gaia catalog
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Note on table1.dat: The second realization of the International Celestial
Reference Frame (ICRF2) is based on Very Long Baseline Interferometry (VLBI)
data at radio frequencies in X band and S band. The European Space Agency's
Gaia mission, launched on 2013 December 19, started routine scientific
operations in 2014 July. By scanning the whole sky, it is expected to observe
∼500000 Quasi Stellar Objects in the optical domain. This means that, in the
future, two extragalactic celestial reference frames, at two different
frequency domains, will coexist. It will thus be important to align them very
accurately.
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See also:
I/324 : The Initial Gaia Source List (IGSL) (Smart, 2013)
I/323 : International Celestial Reference Frame 2, ICRF2 (Ma+, 2009)
J/AJ/150/58 : VLBI ICRF2 (Fey+, 2015)
J/A+A/526/A102 : VLBI imaging of 105 extragalactic radio sources
(Bourda+, 2011)
J/A+A/520/A113 : VLBI detection of 398 extragalactic radio sources
(Bourda+, 2010)
J/AJ/127/3587 : VLBI ICRF. II (Fey+, 2004)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- IVS International Very Long Baseline
Interferometry (VLBI) Service (IVS)
identifier (HHMM+DDd, B1950)
10- 19 A10 --- IAU IAU identifier (JHHMM+DDMM format)
21- 22 I2 h RAh Hour of Right Ascension (J2000) (1)
24- 25 I2 min RAm Minute of Right Ascension (J2000) (1)
27- 36 F10.7 s RAs Second of Right Ascension (J2000) (1)
38 A1 --- DE- Sign of the Declination (J2000) (1)
39- 40 I2 deg DEd Degree of Declination (J2000) (1)
42- 43 I2 arcmin DEm Arcminute of Declination (J2000) (1)
45- 54 F10.7 arcsec DEs Arcsecond of Declination (J2000) (1)
56- 59 I4 uarcsec e_RAs [2/1015] Formal error in RAs (2)
61- 64 I4 uarcsec e_DEs [2/1473] Formal error in DEs (2)
66- 69 I4 --- Nexp [10/4592] Number of VLBI sessions
71- 76 I6 --- Nobs [126/401647] Number of VLBI observations
78- 82 F5.2 Jy X-GSFC [0.03/10] Goddard Space Flight Center (GSFC)
IVS Analysis Center X-band flux density (3)
84- 88 F5.2 Jy S-GSFC [0.03/10] Goddard Space Flight Center (GSFC)
IVS Analysis Center S-band flux density (3)
90- 94 F5.2 Jy X-BVID [0.07/13.4]? Bordeaux VLBI Image Database
(BVID) X-band flux density (3)
96-100 F5.2 Jy S-BVID [0.04/10.73]? Bordeaux VLBI Image Database
(BVID) S-band flux density (3)
102 I1 --- Cat [1/4] Initial Gaia category (4)
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Note (1): The coordinates are from the latest version of the Goddard Space
Flight Center (GSFC) solution 2015a in International Earth Rotation and
Reference Systems Service (IERS) format (status: 01 September 1 2015).
Note (2): The uncertainties for e_RAs are not corrected from cos(DE). The formal
errors in the table come directly from the GSFC solution and are likely to
optimistic. A more realistic estimate would be obtained by applying a scale
factor of 1.5 to the formal uncertainties followed by a root-sum-square
increase of 40 micro-arcseconds of error in quadrature to the quoted
values. This was the procedure adopted for ICRF2 (Fey et al. 2009,
http://www.iers.org/TN35; Fey et al. 2015, cat. J/AJ/150/58).
Note (3): The flux values are from sked flux catalog
(ftp://gemini.gsfc.nasa.gov/pub/sked/catalogs/flux.cat;
status: 28 August 2015) and from the Bordeaux Very Long Baseline
Interferometry (VLBI) Image Database (BVID; Collioud & Charlot 2009 Proc.
19th EVGA Working Meeting, European VLBI for Geodesy and Astrometry ed
G. Bourda, P. Charlot and A. Collioud 19; status: 11 September 2015).
The fluxes are computed from data available through 2015 August 27 for the
sked catalog and through 2013 July 24 for BVID (see Section 4.3).
Note (4): The categories are defined as below:
1 = One of 89 sources in the IVS source monitoring program that were
sufficiently observed;
2 = One of 66 sources in the IVS source monitoring program that were not
sufficiently observed;
3 = One of 16 sources not in the IVS source monitoring program but with a
sufficient position accuracy;
4 = One of 24 sources not in the IVS source monitoring program and with
poor position accuracy.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 18-Jul-2016