J/ApJS/274/28 Metrics of astrometric variability in the ICRF. I. (Cigan+, 2024)
Metrics of astrometric variability in the International Celestial Reference
Frame.
I. Statistical analysis and selection of the most variable sources.
Cigan P., Makarov V.V., Secrest N.J., Gordon D., Johnson M.C., Lambert S.
<Astrophys. J. Suppl. Ser., 274, 28 (2024)>
=2024ApJS..274...28C 2024ApJS..274...28C
ADC_Keywords: Interferometry; Radio sources; Positional data; QSOs;
Active gal. nuclei
Keywords: Very long baseline interferometry ; Astrometry ; Quasars ;
Radio sources
Abstract:
Using very long baseline interferometry data for the sources that
comprise the third International Celestial Reference Frame (ICRF3), we
examine the quality of the formal source-position uncertainties of
ICRF3 by determining the excess astrometric variability (unexplained
variance) for each source as a function of time. We also quantify
multiple qualitatively distinct aspects of astrometric variability
seen in the data, using a variety of metrics. Average position
offsets, statistical dispersion measures, and coherent trends over
time as explored by smoothing the data are combined to characterize
the most and least positionally stable ICRF3 sources. We find a
notable dependence of the excess variance and statistical variability
measures on decl., as is expected for unmodeled ionospheric delay
errors and the Northern Hemisphere-dominated network geometries of
most astrometric and geodetic observing campaigns.
Description:
Combining millions of astrometric and geodetic VLBI group delay
measurements observed across 6581 sessions over the course of more
than four decades of international efforts, we have produced time
series of positions on the sky for over 5550 radio sources, including
all 4536 sources comprising the ICRF3 X/S catalog (where the S band at
2.3GHz is used for determining the ionosphere contribution to the
delay, and improving the final solution defined at 8.4GHz in the X band).
This first paper in a planned series of analyses of various aspects of
these time series focuses on the overall statistical aspects of the
position data.
The following work is conducted on 4334 sources drawn from the full
ICFR3 catalog. See Section 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 200 4336 Overall variability metrics by source
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See also:
I/149 : Fifth Fundamental Catalogue (FK5) Part I (Fricke+, 1988)
I/175 : Fifth Fundamental Catalogue (FK5) - Extension (Fricke+ 1991)
I/323 : International Celestial Reference Frame 2, ICRF2 (Ma+, 2009)
J/A+A/529/A91 : Proper motions of 555 quasars from VLBI (Titov+, 2011)
J/A+A/545/A113 : MOJAVE IX. Core shift effects (Pushkarev+, 2012)
J/MNRAS/430/2797 : ICRF2 sources of the Rio survey (Assafin+, 2013)
J/AJ/150/58 : VLBI ICRF2 (Fey+, 2015)
J/ApJ/835/L30 : Dislodged AGNs (Makarov+, 2017)
J/MNRAS/467/L71 : Significance of VLBI/Gaia position offsets (Petrov+, 2017)
J/ApJ/873/132 : ICRF3 radio-loud quasars with Gaia DR2 data (Makarov+, 2019)
J/MNRAS/485/1822 : AGN core shift measurements (Plavin+, 2019)
J/A+A/644/A159 : The third realization of the ICRF, ICRF3 (Charlot+, 2020)
J/A+A/684/A93 : Position and photometric variability (Lambert+, 2024)
http://hpiers.obspm.fr/webiers/newwww/icrf/ : ICRF homepage
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- IERS B1950 Source Name (HHMM+DDd; B1950)
10- 19 A10 --- IDJ2000 J2000 Source Name (JHHMM+DDMM)
21- 45 A25 --- Name Other Source Name (1)
47- 50 I4 --- Nobs [4/4876] Number of diurnal observing
sessions
52- 57 I6 --- Ndelay [45/535391] Number of delay measurements
59- 67 E9.2 mas jitRA [-29/86] Covariance-weighted mean jitter in
RA
69- 77 E9.2 mas jitDEC [-120/69] Covariance-weighted mean jitter
in DEC
79- 86 E8.2 mas jitTOT [0.0018/140] Mean total (RA and DEC) jitter
value
88- 95 E8.2 mas errExcRA [0/98] Excess error in RA
97- 104 E8.2 mas errExcDEC [0/130] Excess error in DEC
106- 113 E8.2 mas errExcTOT [0/170] Total (RA and DEC) excess error
115- 122 E8.2 mas errCombRA [0.03/98] Combined (formal+excess) error in
RA
124- 131 E8.2 mas errCombDEC [0.047/140] Combined (formal+excess) error
in DEC
133- 140 E8.2 mas errCombTOT [0.059/170] Total (RA and DEC) Combined
error
142- 146 F5.2 --- Q68 [0.3/50.2]? Q68, 0.68-quantile of
normalized offsets
148- 155 E8.2 mas wrmsRA [0.024/33] Weighted root mean square of RA
offsets
157- 164 E8.2 mas wrmsDEC [0.029/62] Weighted root mean square of DEC
offsets
166- 173 E8.2 mas wrmsTOT [0.02/62] Total (RA and DEC) wrms
175- 182 E8.2 mas strRA [0/40]? Smoothed Timeseries Range in RA
184- 191 E8.2 mas strDEC [0/58]? Smoothed Timeseries Range in DEC
193- 200 E8.2 mas strTOT [0/57]? STR of Total (RA and DEC) offsets
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Note (1): OI 171 is very likely a misprint for OHIO I 471; corrected at CDS.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 12-Feb-2025