文章基本信息

标题：The Gaia reference frame for bright sources examined using VLBI observations of radio stars
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作者：Lennart Lindegren
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2020
卷号：633
页码：1-17
DOI：10.1051/0004-6361/201936161
语种：English
出版社：EDP Sciences
摘要：Context.Positions and proper motions ofGaiasources are expressed in a reference frame that ideally should be non-rotating relative to distant extragalactic objects, coincident with the International Celestial Reference System (ICRS), and consistent across all magnitudes. For sources fainter than 16th magnitude, this is achieved throughGaia’s direct observations of quasars. At brighter magnitudes, it is difficult to validate the quality of the reference frame because comparison data are scarce.Aims.The aim of this paper is to examine the use of very long baseline interferometry (VLBI) observations of radio stars to determine the spin and orientation of the bright reference frame of current and futureGaiadata releases.Methods.Simultaneous estimation of the six spin and orientation parameters makes optimal use of VLBI data and makes it possible to include even single-epoch VLBI observations in the solution. The method is applied toGaiaData Release 2 (DR2) using published VLBI data for 41 radio stars.Results.The VLBI data for the best-fitting 26 sources indicate that the bright reference frame ofGaiaDR2 rotates relative to the faint quasars at a rate of about 0.1 mas yr−1, which is significant at the 2σlevel. This supports a similar conclusion based on a comparison with stellar positions in the HIPPARCOSframe. The accuracy is currently limited because only a few radio sources are included in the solution, by uncertainties in theGaiaDR2 proper motions, and by issues related to the astrophysical nature of the radio stars.Conclusions.While the origin of the indicated rotation is understood and can be avoided in future data releases, it remains important to validate the bright reference frame ofGaiaby independent observations. This can be achieved using VLBI astrometry, which may require re-observing the old sample of radio stars as well as measuring new objects. The unique historical value of positional measurements is stressed and VLBI observers are urged to ensure that relevant positional information is preserved for the future.
关键词：enastrometryproper motionsreference systemsinstrumentation: interferometersmethods: data analysis