J/A+A/618/A80 Astrometric classification of 647 VLBI sources (Gattano+, 2018)
Extragalactic radio source stability and VLBI celestial reference frame:
insights from the Allan standard deviation.
Gattano C., Lambert S., Le Bail K.
<Astron. Astrophys. 618, A80 (2018)>
=2018A&A...618A..80G 2018A&A...618A..80G (SIMBAD/NED BibCode)
ADC_Keywords: Fundamental catalog ; Active gal. nuclei ; Positional data ;
Interferometry ; Redshifts ; Radio sources
Keywords: techniques: interferometric - astrometry - reference systems
Abstract:
We present the result of our Allan standard deviation based
classification according to their astrometric stability. The
classification is divided into three categories (stable sources,
intermediate sources, unstable sources). Stability of sources is
qualified by the astrometric behavior of the source. This determines
in which category the source falls into. Then, stability of the source
is also quantified by a stability index (two are proposed in the
table). Those indexes enable to order sources in each category of the
classification.
Description:
Each row in the table is associated to one VLBI source, candidate to
the definition of the celestial reference frame in the sense that the
source has been observed in at least 20 sessions of observation
approved by our outlier cleaning. Most of the information is computed
from offset time series from the mean position of the source. The
classification is user dependent. Columns 22 and 23 gives the category
of the source according to each equatorial coordinate. Worst of both
(col. 24) gives the intermediate category of the source. A statistical
process then enables to possibly rehabilitate intermediate and
unstable sources into the stable category under statistical validation
arguments (see the paper for all the details). One has to choose a
rehabilitation threshold, compare col. 25 (resp. 26) value with the
threshold and change col. 22 (resp. 23) if the value is greater than
the threshold. By being the worst of both columns 22 and 23, col. 24
may change in consequence and gives the final category of the source.
In order to avoid user to mistaken when proceeding to the
rehabilitation process, a dedicated webpage has been developped in
this purpose. The web page can be found at
http://www.cgattano-astrogeoresearch.fr/GattanoLambertLeBail2018
We recommand its usage.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
adevclas.dat 328 647 ADEV based classification of VLBI sources
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See also:
I/323 : International Celestial Reference Frame 2, ICRF2 (Ma+, 2009)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/614/A140 : Large Quasar Astrometric Catalogue 4, LQAC-4 (Gattano+, 2018)
Byte-by-byte Description of file: adevclas.dat
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Bytes Format Units Label Explanations
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3- 10 A8 --- IVSname International VLBI Service (IVS) name
13- 20 A8 --- IERSname International Earth Rotation and Reference
Systems Service (IERS) name
(HHMM+DDd, B1950 equinox)
28 A1 --- ICRF2 [-1 0 2] Status in ICRF2 (2)
31- 46 F16.12 deg RAdeg VLBI right ascension (J2000.0), values from
ICRF2, cat. I/323
50- 64 F15.11 deg DEdeg VLBI declination (J2000.0), values
from ICRF2, cat. I/323
71- 76 F6.4 mas e_RAdeg Inflated formal error in VLBI right ascension
(values from ICRF2, cat. I/323)
82- 88 F7.4 mas e_DEdeg Inflated formal error in VLBI declination
(values from ICRF2, cat. I/323)
90-106 F17.12 deg RAGdeg ?=-999.0 Gaia right ascension (J2015.5),
values from Gaia DR2, cat. I/345
109-124 F16.11 deg DEGdeg ?=-999.0 Gaia declination (J2015.5),
values from Gaia DR2, cat. I/345
128-136 F9.4 mas e_RAGdeg ?=-999.0 Standard error of Gaia right
ascension (values from Gaia DR2, cat. I/345)
140-148 F9.4 mas e_DEGdeg ?=-999.0 Standard error of Gaia declination
(values from Gaia DR2, cat. I/345)
151-154 I4 --- Nsess Number of sessions (3)
157-164 F8.3 yr EpochF [1979.5/2017.6] First Date (4)
167-174 F8.3 yr EpochM [1979.5/2017.6] Median Date (4)
177-184 F8.3 yr EpochL [1979.5/2017.6] Last Date (4)
191-196 F6.4 mas wrmsoRA* Classical stability index on RA* (5)
203-208 F6.4 mas wrmsoDE Classical stability index on DE (6)
215-220 F6.4 mas CStabInd Classical stability index (7)
227-232 F6.4 mas wADEVoRA* Alternative stability index on RA* (8)
239-244 F6.4 mas wADEVoDE Alternative stability index on DE (9)
251-256 F6.4 mas AStabInd Alternative stability index (10)
266 A1 --- ClassRA* [012] Category on the basis of RA* (11)
274 A1 --- ClassDE [012] Category on the basis of DE (11)
282 A1 --- Class [012] Category of the source (before any
rehabilitation process) (11)(12)
291-292 I2 % PwnRA* Rehabilitation probability for RA* (13)
297-298 I2 % PwnDE Rehabilitation probability for DE (13)
300-308 F9.4 --- z ?=-999.0 Spectroscopic redshift
311-318 F8.3 mag Bmag ?=-999.0 Photometric magnitude in B band
(between 400 and 500nm)
321-328 F8.3 Jy S8.4 ?=-999.0 Radio flux at 8.4GHz
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Note (2): Status in ICRF2 as follows:
-1 = absent
0 = defining source
1 = standard source
2 = special handling source
Note (3): number of sessions in which the source is observed
(after outlier treatment).
Note (4): taken from the time series cleaned from outliers.
Note (5): Classical stability index on RAcos(DE) computed as the wrms of the
offset time series from the mean RAcos(mean DE) (after the outlier treatment).
Note (6): Classical stability index on Declination computed as the wrms of the
offset time series from the mean Declination (after the outlier treatment).
Note (7): Global classical stability index computed as
sqrt( (wrmsoRA*)**2*(chioRA*)**2 + (wrmsoDE)**2*(chioDE)**2 )
of the offset time series from the mean position (after outliers treatment).
Note (8): Alternative stability index (upper limit) on RAcosDE computed
as the value at 10 years time-scale of the Allan standard deviation function
of the Lowest Maximizing White Noise [LMWN] that maximizes the Allan standard
deviation function of the RAcosDE offset time series of the source
(after outliers treatment)
Note (9): Alternative stability index (upper limit) on Declination computed as
the value at 10 years time-scale of the Allan standard deviation function of
the Lowest Maximizing White Noise [LMWN] that maximizes the Allan standard
deviation function of the Declination offset time series of the source
(after outliers treatment) .
Note (10): Global alternative stability index (upper limit) computed as
sqrt( (wADEVoRA*)**2 + (wADEVoDE)**2 )
of the offset time series from the mean position (after outliers treatment).
Note (11): in our Allan standard deviation based classification as follows:
0 = stable behavior
1 = intermediate behavior
2 = unstable behavior
Note (12): worst of the two previous categories on the basis of both coordinates
as follows:
0 = stable behavior
1 = intermediate behavior
2 = unstable behavior
Note (13): computed from the Monte-Carlo test in the rehabilitation process. It
enables to consider intermediate behaviors and unstable behaviors as stable
sources regarding statistical arguments (see the paper for details).
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Acknowledgements:
Gattano Cesar, cesar.gattano(at)u-bordeaux.fr
LAB/CNES/OASU/Univ. Bordeaux/CNRS
(End) Cesar Gattano [LAB/CNES, France], Patricia Vannier [CDS] 12-Jul-2018