The Identification of BHB Stars Using GALEX and other photometry

TL;DR

This paper demonstrates that combining GALEX near-UV photometry with optical data effectively distinguishes blue horizontal branch stars from other A stars, improving identification accuracy in halo samples.

Contribution

The study introduces a new photometric method using GALEX NUV data combined with optical magnitudes to reliably identify BHB stars, extending previous techniques.

Findings

GALEX NUV data enhances BHB star identification.

The (NUV - V)_0 vs. (B-V)_0 plot effectively separates BHB stars.

Method extends to fainter magnitudes with GALEX Medium-Deep Survey.

Abstract

Halo samples that have no kinematic bias have been successfully isolated by photometric observations. We show that the near-UV (NUV) magnitude of the GALEX All-Sky Survey can be used, together with Johnson BV magnitudes in a (NUV-V)_0 vs. (B-V)_0 plot, to distinguish blue horizontal branch (BHB) from other A stars of the same B-V color for 12<V<18. In addition, we use SDSS gr magnitudes in a (NUV - r)_0 vs. (g-r)_0 plot for 14<r<18. The faint limit will be extended by ~3 magnitudes for the GALEX Medium-Deep Survey. Attempts to use NUV in conjunction with 2MASS magnitudes and ROTSE m_r magnitudes did not prove useful. The (NUV - V)_0 vs. (B-V)_0 plot was used to examine BHB star candidates of varying quality near the South Galactic Pole. We conclude that the addition of the GALEX NUV significantly adds to the reliabilty with which these stars can be identified.