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Gaia Data Release 2 : The celestial reference frame (Gaia -CRF2)

Mignard, F. ; Klioner, S. A. ; Lindegren, L. LU orcid ; Hernández, J. ; Bastian, U. ; Bombrun, A. ; Hobbs, D. LU orcid ; Lammers, U. ; Michalik, D. LU and Ramos-Lerate, M. , et al. (2018) In Astronomy and Astrophysics 616.
Abstract

Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the optical domain. A subset of these quasars have accurate VLBI positions that allow the axes of the reference frame to be aligned with the International Celestial Reference System (ICRF) radio frame. Aims. We describe the astrometric and photometric properties of the quasars that were selected to represent the celestial reference frame of Gaia DR2 (Gaia-CRF2), and to compare the optical and radio positions for sources with accurate VLBI positions. Methods. Descriptive statistics are used to characterise the overall properties of the quasar sample.... (More)

Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the optical domain. A subset of these quasars have accurate VLBI positions that allow the axes of the reference frame to be aligned with the International Celestial Reference System (ICRF) radio frame. Aims. We describe the astrometric and photometric properties of the quasars that were selected to represent the celestial reference frame of Gaia DR2 (Gaia-CRF2), and to compare the optical and radio positions for sources with accurate VLBI positions. Methods. Descriptive statistics are used to characterise the overall properties of the quasar sample. Residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. Positional differences are calculated relative to a prototype version of the forthcoming ICRF3. Results. Gaia-CRF2 consists of the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues. The sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range G ≈ 16 to 21 mag with accurately known optical positions. The median positional uncertainty is 0.12 mas for G < 18 mag and 0.5 mas at G = mag. Large-scale systematics are estimated to be in the range 20 to 30 μas. The accuracy claims are supported by the parallaxes and proper motions of the quasars in Gaia DR2. The optical positions for a subset of 2820 sources in common with the ICRF3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions. Conclusions. Based on less than 40% of the data expected from the nominal Gaia mission, Gaia-CRF2 is the first realisation of a non-rotating global optical reference frame that meets the ICRS prescriptions, meaning that it is built only on extragalactic sources. Its accuracy matches the current radio frame of the ICRF, but the density of sources in all parts of the sky is much higher, except along the Galactic equator.

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Contribution to journal
publication status
published
subject
keywords
Astrometry, Catalogs, Reference systems
in
Astronomy and Astrophysics
volume
616
article number
A14
publisher
EDP Sciences
external identifiers
  • scopus:85051866064
ISSN
0004-6361
DOI
10.1051/0004-6361/201832916
language
English
LU publication?
yes
id
9da4e4da-640e-4af1-964a-d389b7122880
date added to LUP
2019-04-29 14:19:09
date last changed
2024-04-16 04:41:12
@article{9da4e4da-640e-4af1-964a-d389b7122880,
  abstract     = {{<p>Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the optical domain. A subset of these quasars have accurate VLBI positions that allow the axes of the reference frame to be aligned with the International Celestial Reference System (ICRF) radio frame. Aims. We describe the astrometric and photometric properties of the quasars that were selected to represent the celestial reference frame of Gaia DR2 (Gaia-CRF2), and to compare the optical and radio positions for sources with accurate VLBI positions. Methods. Descriptive statistics are used to characterise the overall properties of the quasar sample. Residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. Positional differences are calculated relative to a prototype version of the forthcoming ICRF3. Results. Gaia-CRF2 consists of the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues. The sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range G ≈ 16 to 21 mag with accurately known optical positions. The median positional uncertainty is 0.12 mas for G &lt; 18 mag and 0.5 mas at G = mag. Large-scale systematics are estimated to be in the range 20 to 30 μas. The accuracy claims are supported by the parallaxes and proper motions of the quasars in Gaia DR2. The optical positions for a subset of 2820 sources in common with the ICRF3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions. Conclusions. Based on less than 40% of the data expected from the nominal Gaia mission, Gaia-CRF2 is the first realisation of a non-rotating global optical reference frame that meets the ICRS prescriptions, meaning that it is built only on extragalactic sources. Its accuracy matches the current radio frame of the ICRF, but the density of sources in all parts of the sky is much higher, except along the Galactic equator.</p>}},
  author       = {{Mignard, F. and Klioner, S. A. and Lindegren, L. and Hernández, J. and Bastian, U. and Bombrun, A. and Hobbs, D. and Lammers, U. and Michalik, D. and Ramos-Lerate, M. and Biermann, M. and Fernández-Hernández, J. and Geyer, R. and Hilger, T. and Siddiqui, H. I. and Steidelmüller, H. and Babusiaux, C. and Barache, C. and Lambert, S. and Andrei, A. H. and Bourda, G. and Charlot, P. and Vallenari, A. and Prusti, T. and De Bruijne, J. H.J. and Bailer-Jones, C. A.L. and Evans, D. W. and Eyer, L. and Jansen, F. and Jordi, C. and Luri, X. and Panem, C. and Pourbaix, D. and Randich, S. and Sartoretti, P. and Soubiran, C. and Van Leeuwen, F. and Walton, N. A. and Arenou, F. and Cropper, M. and Drimmel, R. and Katz, D. and Lattanzi, M. G. and Bakker, J. and Cacciari, C. and Castañeda, J. and Chaoul, L. and Cheek, N. and Holl, B. and McMillan, P. J.}},
  issn         = {{0004-6361}},
  keywords     = {{Astrometry; Catalogs; Reference systems}},
  language     = {{eng}},
  month        = {{08}},
  publisher    = {{EDP Sciences}},
  series       = {{Astronomy and Astrophysics}},
  title        = {{Gaia Data Release 2 : The celestial reference frame (Gaia -CRF2)}},
  url          = {{http://dx.doi.org/10.1051/0004-6361/201832916}},
  doi          = {{10.1051/0004-6361/201832916}},
  volume       = {{616}},
  year         = {{2018}},
}