New Pleiades Eclipsing Binaries and a Hyades Transiting System Identified by K2

Abstract

We present the discovery in Kepler's $K2$ mission observations and our follow-up radial velocity observations from Keck/HIRES for four eclipsing binary (EB) star systems in the young benchmark Pleiades cluster. Based on our modeling results, we announce two new low mass ($M_{tot} < 0.6 M_\odot$) EBs among Pleiades members (HCG 76 and MHO 9) and we report on two previously known Pleiades binaries that are also found to be EB systems (HII 2407 and HD 23642). We measured the masses of the binary HCG 76 to $\lesssim$2.5% precision, and the radii to $\lesssim$4.5% precision, which together with the precise effective temperatures yield an independent Pleiades distance of 132$\pm$5 pc. We discuss another EB towards the Pleiades that is a possible but unlikely Pleiades cluster member (AK II 465). The two new confirmed Pleiades systems extend the mass range of Pleiades EB components to 0.2-2 $M_\odot$. Our initial measurements of the fundamental stellar parameters for the Pleiades EBs are discussed in the context of the current stellar models and the nominal cluster isochrone, finding good agreement with the stellar models of Baraffe et al. (2015) at the nominal Pleiades age of 120 Myr. Finally, in the Hyades, we report a new low mass eclipsing system (vA 50) that was concurrently discovered and studied by Mann et al. (2016). We confirm that the eclipse is likely caused by a Neptune-sized transiting planet, and with the additional radial velocity constraints presented here we improve the constraint on the maximum mass of the planet to be $\lesssim$1.2 $M_\mathrm{Jup}$.