Catalogues of Blue Horizontal Branch Stars

This has been deemed important as the success of the Gaia mission has changed the way that targets are selected for large-scale spectroscopic surveys, meaning that far fewer spectra will be acquired for blue horizontal-branch stars in the future unless they are specifically targeted. We cross-matched reference blue horizontal-branch datasets with the Gaia DR2 database and defined two sets of selection criteria. Firstly, in Gaia DR2 - colour and absolute G magnitude space, and secondly, in Gaia DR2 - colour and reduced proper motion space.

The main-sequence contamination in both subsets of the catalogue was reduced, at the expense of completeness, by concentrating on the Milky Way's Galactic halo, where relatively young main-sequence stars were not expected. The entire catalogue is limited to those stars with no apparent neighbours within 5 arcsec. These methods were verified and subsequently applied to theGaia Early Data Release 3 (EDR3).

We present a catalogue, based on Gaia EDR3, of 57377 blue horizontal-branch stars. The Gaia EDR3 parallax was used in selecting 16794 candidates and the proper motions were used to identify a further 40583 candidates.