Precise and Accurate Mass and Radius Measurements of Thirty Galactic Metal-Poor Stars in Detached Eclipsing Binaries

Abstract

Detached eclipsing binaries have long served as fundamental benchmarks for making direct comparisons with stellar models. By combining the light curve and radial velocity orbit of a detached eclipsing binary, precise masses and radii can be measured for both components. However, catalogs of eclipsing binaries are dominated by solar-metallicity stars. Here we characterize fifteen eclipsing binaries selected to have $[\rm{M/H}]\lesssim -0.5$ using TESS photometry, Gaia XP spectra, large spectroscopic surveys, and Galactic kinematics. We use three spectrographs, PEPSI on the Large Binocular Telescope, the Levy spectrograph on the Automated Planet Finder telescope, and CHIRON on the SMARTS 1.5m telescope. We jointly model the light curves and radial velocities and measure the stellar masses and radii with median fractional uncertainties of<1%. We use spectral disentangling to extract the spectra of both stars and model them using the spectral synthesis code Korg. We find three systems with $[\rm{M/H}]<-2.0$, two of which are kinematically consistent with the Milky Way's halo. J0001+2156 has $[\rm{M/H}]=-2.51$, making it the most metal-poor detached eclipsing binary characterized to date. Eleven of the twelve other systems have $[\rm{M/H}] \lesssim -0.5$ and are split between being highly ($[\alpha/\rm{M}]>0.25$) and moderately ($[\alpha/\rm{M}]<0.25$) $\alpha$-enhanced. We compare our measured masses and radii to predictions from theoretical isochrones and estimate the ages of the binaries. We estimate ages with typical uncertainties of $\lesssim 0.5$ Gyr, and three of the binaries have estimated ages greater than 10 Gyr, up to $13.8^{+0.8}_{-0.7}$ Gyr. Finally, we update the empirical relations for stellar masses and radii on the main sequence using a sample of 621 stars.