The Tycho-Gala astrometric solution. How to get 2.5 million parallaxes with less than one year of Gala data
Context. The first release of astrometric data from Gala will contain the mean stellar positions and magnitudes from the first year of observations, and proper motions from the combination of Gala data with HIPPARCOS prior information (HTPM). Aims. We study the potential of using the positions from the Tycho-2 Catalogue as additional information for a joint solution with early Gala data. We call t