The Interferometric Binary Epsilon Cancri in Praesepe: Precise Masses and Age

Abstract

We observe the brightest member of the Praesepe cluster, Cnc, to precisely measure the characteristics of the stars in this binary system, en route to a new measurement of the cluster's age. We present spectroscopic radial velocity measurements and interferometric observations of the sky-projected orbit to derive the masses, which we find to be M 1 /M = 2.420 ± 0.008 and M 2 /M = 2.226 ± 0.004. We place limits on the color-magnitude positions of the stars by using spectroscopic and interferometric luminosity ratios while trying to reproduce the spectral energy distribution of Cnc. We re-examine the cluster membership of stars at the bright end of the color-magnitude diagram using Gaia data and literature radial velocity information. The binary star data are consistent with an age of 637 ± 19 Myr, as determined from MIST model isochrones. The masses and luminosities of the stars appear to select models with the most commonly used amount of convective core overshooting.