11.2.1 Use of astrometric data in Apsis

Author(s): Orlagh L. Creevey

The astrometry provided by CU3 (Chapter 4) was used in the following Apsis modules: DSC, OA, GSP-Phot, FLAME, ESP-UCD and MSC. The stellar-based modules used only the parallax information, while DSC and OA also used the proper motions. We implemented a systematic correction to the parallaxes at the beginning of the Apsis chain, as proposed by Lindegren et al. (2021a) who reports biases that vary with magnitude, color and ecliptic latitude. This bias is corrected using the data from gaia_source as appears in Gaia EDR3: phot_g_mean_mag, astrometric_params_solved, nu_eff_used_in_astrometry, pseudocolour, and ecl_lat. CU8 results using parallaxes are therefore based on the corrected parallax and not gaia_source.parallax.