A new calibration for the Blue Horizontal Branch

TL;DR

This paper introduces a simple analytic formula for estimating distances to Blue Horizontal Branch stars using Sloan colours, validated with SDSS data, improving upon previous methods by including metallicity dependence.

Contribution

It provides a novel, closed-form distance calibration for BHB stars that accounts for metallicity and is validated directly on field stars from SDSS.

Findings

The calibration accurately measures BHB star distances.

It captures metallicity dependence in the distance estimates.

The method is applicable to other star samples and filters.

Abstract

We suggest a simple analytic approximation for magnitudes and hence distances of Blue Horizontal Branch (BHB) stars in Sloan colours. Precedent formulations do not offer a simple closed formula, nor do they cover the full dependences, e.g. on metallicity. Further, using BHB star samples from the Sloan Digital Sky Survey (SDSS) we validate our distance calibration directly on field stars instead of globular clusters and assess the performance of other available distance calibrations. Our method to statistically measure distances is sufficiently accurate to measure the colour and metallicity dependence on our sample and can be applied to other sets of stars or filters.