Angular Diameters of the G Subdwarf $\mu$ Cassiopeiae A and the K Dwarfs $\sigma$ Draconis and HR 511 from Interferometric Measurements with the CHARA Array

TL;DR

This study measures the angular diameters of a halo star and two K dwarfs using the CHARA Array, revealing discrepancies with stellar models and providing insights into low-metallicity star properties.

Contribution

First direct interferometric measurement of a halo star's diameter, comparing it with similar stars to explore metallicity effects on stellar parameters.

Findings

$ m =5297\u00b132$ K for  Cas A

Discrepancy between observed and predicted stellar models for low-metallicity stars

Comparable radii and luminosities among stars with different metallicities

Abstract

Using the longest baselines of the CHARA Array, we have measured the angular diameter of the G5 V subdwarf $\mu$ Cas A, the first such determination for a halo population star. We compare this result to new diameters for the higher metallicity K0 V stars, $\sigma$ Dra and HR 511, and find that the metal-poor star, $\mu$ Cas A, has an effective temperature ($T_{\rm eff}=5297\pm32$ K), radius ($R=0.791\pm0.008 R_{\rm \odot}$), and absolute luminosity ($L=0.442\pm0.014 L_{\rm \odot}$) comparable to the other two stars with later spectral types. We show that stellar models show a discrepancy in the predicted temperature and radius for $\mu$ Cas A, and we discuss these results and how they provide a key to understanding the fundamental relationships for stars with low metallicity.