The Tycho-Gaia Astrometric Solution

Research output: Contribution to journalReview article


Gaia DR1 is based on the first 14 months of Gaia's observations. This is not long enough to reliably disentangle the parallax effect from proper motion. For most sources, therefore, only positions and magnitudes are given. Parallaxes and proper motions were nevertheless obtained for about two million of the brighter stars through the Tycho-Gaia astrometric solution (TGAS), combining the Gaia observations with the much earlier Hipparcos and Tycho-2 positions. In this review I focus on some important characteristics and limitations of TGAS, in particular the reference frame, astrometric uncertainties, correlations, and systematic errors.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Astronomy, Astrophysics and Cosmology


  • astrometry, Catalogs, reference systems, stars: distances, stars: general
Original languageEnglish
Pages (from-to)41-48
Number of pages8
JournalProceedings of the International Astronomical Union
Issue numberS330
Publication statusPublished - 2017 Apr 1
Publication categoryResearch