Clean catalogues of blue horizontal-branch stars using Gaia EDR3

TL;DR

This paper creates a clean catalogue of blue horizontal-branch stars using Gaia EDR3 data, employing photometric and astrometric criteria to identify candidates with low contamination, aiding studies of Galactic structure.

Contribution

The study verifies and applies selection methods for blue horizontal-branch stars to Gaia EDR3, resulting in a large, refined catalogue with improved candidate identification.

Findings

Catalogue of 57,377 blue horizontal-branch stars

Identification of 16,794 candidates via parallax

Identification of 40,583 candidates via proper motions

Abstract

Context: Blue horizontal-branch stars are very old objects that can be used as markers in studies of the Galactic structure and formation history. To create a clean sky catalogue of blue horizontal-branch stars, we cross-matched the Gaia data release 2 (DR2) dataset with existing reference catalogues to define selection criteria based on Gaia DR2 parameters. Following the publication of Gaia early data release 3 (EDR3), these methods were verified and subsequently applied to this latest release. Aims: The purpose of this catalogue is to identify a set of blue horizontal-branch star candidates that have been selected using photometric and astrometric observations and exhibits a low contamination rate. Methods: 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. Results: We present a catalogue, based on Gaia EDR3, of 57,377 blue horizontal-branch stars. The Gaia EDR3 parallax was used in selecting 16,794 candidates and the proper motions were used to identify a further 40,583 candidates.