Probing the inner Galactic Halo with blue horizontal branch stars: Gaia DR3 based catalogue with atmospheric and stellar parameters

TL;DR

This paper presents a comprehensive catalogue of over 22,000 blue horizontal-branch stars in the Galactic Halo, derived from Gaia DR3 data and spectral energy distributions, improving selection accuracy and extending previous catalogues.

Contribution

The study introduces an expanded Gaia DR3-based catalogue of BHB stars with stellar parameters derived from SEDs, enhancing previous datasets with improved selection criteria and contamination assessment.

Findings

Catalogue of 9,172 BHB stars with parameters from SEDs.

Extended Gaia DR3 catalogue with 22,335 BHB candidates, 33% larger.

Contamination level estimated at 10%.

Abstract

Context. Stars that are found on the blue horizontal-branch (BHB) have evolved from low-mass stars that have completed their core hydrogen burning main sequence stage and have undergone the helium flash at the end of their red-giant phase. The fact that their luminosity is virtually constant at all effective temperatures also makes them good standard candles. Aims. We provide a catalogue of BHB stars with stellar parameters that have been calculated from spectral energy distributions (SED), as constructed from multiple large-scale photometric surveys. In addition, we update our previous, Gaia Early Data Release 3 catalogue of BHB stars with parallax errors less than 20% by using the SED results to define the selection criteria. Methods. We selected a large dataset of Gaia Data Release 3 (DR3) objects based only on their position in the colour magnitude diagram, tangential velocity and parallax errors. Spectral energy distributions were then used to evaluate contamination levels in the dataset and derive optimised data quality acceptance constraints. This allowed us to extend the Gaia DR3 colour and absolute magnitude criteria further towards the extreme horizontal-branch. The level of contamination found using SED analysis was confirmed by acquiring spectra using the Ondrejov Echelle spectrograph attached to the Perek 2m telescope at the Astronomical Institute of the Czech Academy of Sciences. Results. We present a catalogue of 9,172 Galactic Halo BHB candidate stars with atmospheric and stellar parameters calculated from synthetic SEDs. We also present an extended Gaia DR3 based catalogue of 22,335 BHB candidate stars with a wider range of effective temperatures and Gaia DR3 parallax errors of less than 20%. This represents an increase of 33% compared to the our 2021 catalogue, with a contamination level of 10%.