J/A+A/375/661 Stability of VLBI reference frame (Gontier+, 2001)
Stability of the extragalactic VLBI reference frame
Gontier A.-M., Le Bail K., Feissel M., Eubanks T.M.
<Astron. Astrophys. 375, 661 (2001)>
=2001A&A...375..661G 2001A&A...375..661G
ADC_Keywords: QSOs ; VLBI ; Positional data ; References
Keywords: quasars - techniques: interferometric - astrometry - reference systems
Description:
The file table 2 gives the results of various tests and noise
measurements performed on time serie of extragalactic radio source
coordinates. Systematic and random behaviours in time serie of
individual determinations of cooordinates for 283 sources over
1987-1999 are investigated. The random variability of the source
coordinates is characterized by the χ2 test (Bevington, 1969,
p.187) and the "goodness of fit (gof)" (Bevington, 1969, p.188).
The Allan variance method (Allan, 1966, Proc. IEEE, vol. 54, 221) is
used to investigate spectral characteristics of the time series.
The source structure index (Fey & Charlot, 1997ApJS..111...95F 1997ApJS..111...95F,
2000, Cat. J/ApJS/128/17) qualifies the level of position
disturbance expected at the date of the map (1 for the less
disturbed, 4 for the most disturbed).
The estimation of "linear rates" in the coordinates is a qualifier of
the systematic parts of the source instability. This table contains
the 283 best observed sources and is divided in three parts, with the
left hand side giving general information and counts, the middle part
giving statistics in the source local frame, and the right hand side
giving statistics in the equatorial frame.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 96 264 Observational and statistical characteristics of
the sources over 1987-1999, in the local and
equatorial coordinate systems
table2.tex 76 626 LaTeX version of the table
--------------------------------------------------------------------------------
See also:
J/AJ/110/880 : Radio reference frame (Johnston+ 1995)
J/ApJS/128/17 : VLBA obs. of radio reference frame sources. III. (Fey+, 2000)
I/171 : Astrographic Catalog Reference Stars (ACRS) (Corbin+ 1991)
I/172 : International Reference Stars (IRS) (Corbin 1991)
I/246 : The ACT Reference Catalog (Urban+ 1997)
I/251 : VLBI International Celestial Reference Frame (ICRF) (Ma+, 1997)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- IERS IERS designation of the radio source
10 A1 --- n_IERS [dcon] ICRF status of the source (1)
12- 15 I4 --- Nses Number of sessions with more than two
observations of the source.
17- 18 I2 --- Nyears Number of years with observations of the
source in at least six sessions.
20- 22 I3 deg Angle ? Angle of the axis of maximum local
variability with the declination axis.
24 A1 --- l_gofPos Limit flag on gofPos
25- 29 F5.1 --- gofPos Goodness of fit of the yearly coordinate in
the direction of maximum local variability.
31- 36 F6.2 --- e_Pos ? Allan standard error of yearly coordinate in
the direction of maximum local variability
38 I1 --- Index ? Fey & Charlot (1997ApJS..111...95F 1997ApJS..111...95F and 2000,
Cat. J/ApJS/128/17) source structure index
40- 43 I4 yr EpIndex ? Epoch of source structure index
45 A1 --- Noise [WF] Spectral type of noise in the direction
of maximum local variability:
White noise (W) or Flicker noise (F).
47- 51 F5.2 mas/yr Rate ? Rate of apparent motion in the direction of
maximum local variability
53- 56 F4.2 mas/yr e_Rate ? rms uncertainty on Rate
58 A1 --- n2RA [#] # marks poor estimates
59- 62 F4.1 --- 2_RA ? χ2 of individual right ascensions
64 A1 --- lgof2RA Limit flag on gof2_RA
65- 69 F5.1 --- gof2_RA Goodness of fit of yearly right ascensions
71- 75 F5.2 --- e_RAcosDE ? Allan standard error of yearly RAcosDE
77 A1 --- n2DE [#] # marks poor estimates
78- 81 F4.1 --- 2_DE ? χ2 of individual declinations
83 A1 --- lgof2RE Limit flag on gof2_RE
84- 89 F6.1 --- gof2_RE Goodness of fit of yearly declinations
91- 96 F6.2 --- e_DE ? Allan standard error of yearly declinations
--------------------------------------------------------------------------------
Note (1): ICRF status of the source:
d: definition
c: candidate
o: other
n: new
--------------------------------------------------------------------------------
Acknowledgements: Anne-Marie Gontier
References:
Bevington, P.R. 1969, Data reduction and Error analysis for the
physical sciences, McGraw-Hill, New York.
(End) Patricia Bauer [CDS] 09-Jul-2001