The Distances to Open Clusters from Main-Sequence Fitting. I. New Models and a Comparison to the Properties of the Hyades Eclipsing Binary vB 22

TL;DR

This paper develops new stellar evolution models to determine open cluster distances, compares them with the Hyades eclipsing binary data, and discusses discrepancies in stellar radii and helium abundance.

Contribution

It introduces updated models for open cluster distance estimation and examines their consistency with observed binary star properties, highlighting a radius discrepancy.

Findings

Good agreement in luminosities between models and vB 22

Discrepancy in stellar radii inferred from eclipse data

Derived helium abundance for Hyades similar to the Sun

Abstract

In the first of a new series of papers on open cluster distances, we use updated stellar evolution models to construct an isochrone appropriate for the Hyades, and compare it with the Hyades eclipsing binary system vB 22. We find that the absolute and relative luminosities of the two stars are in good agreement with the model, but the radii do not match the values inferred from eclipse data. We present evidence that there is a consistency problem with the flux ratios and the inferred radii, and discuss possible theoretical effects that could be responsible for the mismatch in the radii. We derive a helium abundance for the Hyades of Y = 0.271 \pm 0.006, which is equal within the errors to the Sun's initial helium abundance even though the Hyades is considerably more metal-rich.