GaiaData Release 1

Abstract

Context. Gaia Data Release 1 (DR1) contains astrometric results for more than 1 billion stars brighter than magnitude 20.7 based on observations collected by the Gaia satellite during the first 14 months of its operational phase. Aims. We give a brief overview of the astrometric content of the data release and of the model assumptions, data processing, and validation of the results. Results. For about two million of the brighter stars (down to magnitude ∼11.5) we obtain positions, parallaxes, and proper motions to Hipparcostype precision or better. For these stars, systematic errors depending for example on position and colour are at a level of ±0.3 milliarcsecond (mas). For the remaining stars we obtain positions at epoch J2015.0 accurate to ∼10 mas. Positions and proper motions are given in a reference frame that is aligned with the International Celestial Reference Frame (ICRF) to better than 0.1 mas at epoch J2015.0, and non-rotating with respect to ICRF to within 0.03 mas yr −1 . The Hipparcos reference frame is found to rotate with respect to the Gaia DR1 frame at a rate of 0.24 mas yr −1 . Conclusions. Based on less than a quarter of the nominal mission length and on very provisional and incomplete calibrations, the quality and completeness of the astrometric data in Gaia DR1 are far from what is expected for the final mission products. The present results nevertheless represent a huge improvement in the available fundamental stellar data and practical definition of the optical reference frame.

ESTIMATING DISTANCES FROM PARALLAXES. III. DISTANCES OF TWO MILLION STARS IN THE Gaia DR1 CATALOGUE

“…13 of Paper II which shows the same plot for GUMS data 1 ), which reflects the preliminary nature of GDR1. The upper limit of 1 mas is due to the imposed σ = 1 mas cutoff to reject unreliable astrometric solutions, while the lower limit is due to the ∼0.2 mas noise floor which is dominated by the satellite attitude and calibration uncertainties (Lindegren, L. et al 2016). Future data releases will be much more precise (Gaia Collaboration et al 2016a).…”

“…The primary astrometric data set in this release lists the positions, parallaxes, and proper motions of 2 057 050 stars which are in the Tycho-2 (Høg et al 2000) catalogue (93 635 of the these are Hipparcos (Perryman et al 1997;van Leeuwen 2007) sources). This data set is called the Tycho-Gaia astrometric solution (TGAS; Michalik et al 2015;Lindegren, L. et al 2016).…”

“…The 5-parameter astrometric solutions for TGAS stars were obtained by combining Gaia observations with the positions and their uncertainties of the Tycho-2 stars (with an observation epoch of around J1991) as prior information (Lindegren, L. et al 2016). This was necessary because the observation baseline in the early Gaia data was insufficient for a Gaia-only solution.…”

“…This was necessary because the observation baseline in the early Gaia data was insufficient for a Gaia-only solution. The resulting solutions have median parallax uncertainties of ∼0.3 mas, with an additional systematic uncertainty of about ∼0.3 mas (Gaia Collaboration et al 2016a;Lindegren, L. et al 2016).…”

First Gaia Local Group Dynamics: Magellanic Clouds Proper Motion and Rotation

“…By contrast, the Gaia DR1 of Sep 14, 2016(Gaia Collaboration et al 2016b, includes PMs only for stars in common between Gaia and the Hipparcos Tycho-2 Catalogue (Hoeg et al 2000). This Tycho-Gaia Astrometric Solution (TGAS) Catalog (Lindegren et al 2016) is restricted to the same bright stars previously studied by Hipparcos and is therefore not well suited for studies of Local Group dynamics. However, we show in this paper that it does yield some first new insights.…”