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Joint astrometric solution of HIPPARCOS and Gaia<br>A recipe for the Hundred Thousand Proper Motions project

Joint astrometric solution of HIPPARCOS and Gaia
A recipe for the Hundred Thousand Proper Motions project

Publication date: 14 November 2014

Authors: Michalik, D., et al.

Journal: Astronomy & Astrophysics
Volume: 571
Page: A85
Year: 2014

Copyright: © ESO, 2014

Context. The first release of astrometric data from Gaia is expected in 2016. It will contain the mean stellar positions and magnitudes from the first year of observations. For more than 100 000 stars in common with the Hipparcos Catalogue it will be possible to compute very accurate proper motions due to the time difference of about 24 years between the two missions. This Hundred Thousand Proper Motions (HTPM) project is planned to be part of the first release.
Aims. Our aim is to investigate how early Gaia data can be optimally combined with information from the Hipparcos Catalogue in order to provide the most accurate and reliable results for HTPM.
Methods. The Astrometric Global Iterative Solution (AGIS) was developed to compute the astrometric core solution based on the Gaia observations and will be used for all releases of astrometric data from Gaia. We adapt AGIS to process Hipparcos data in addition to Gaia observations, and use simulations to verify and study the joint solution method.
Results. For the HTPM stars we predict proper motion accuracies between 14 and 134 μas yr-1, depending on stellar magnitude and amount of Gaia data available. Perspective effects will be important for a significant number of HTPM stars, and in order to treat these effects accurately we introduce a formalism called scaled model of kinematics (SMOK). We define a goodness-of-fit statistic which is sensitive to deviations from uniform space motion, caused for example by binaries with periods of 10–50 years.
Conclusions. HTPM will significantly improve the proper motions of the Hipparcos Catalogue well before highly accurate Gaia-only results become available.
[Remainder of abstract truncated due to character limitations]

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