EPIC 219388192 b - an inhabitant of the brown dwarf desert in the Ruprecht 147 open cluster

Abstract

We report the discovery of EPIC 219388192 b, a transiting brown dwarf in a 5.3-day orbit around a member star of Ruprecht-147, the oldest nearby open cluster association, which was photometrically monitored by K2 during its Campaign 7. We combine the K2 time-series data with ground-based adaptive optics imaging and high resolution spectroscopy to rule out false positive scenarios and determine the main parameters of the system. EPIC 219388192 b has a radius of $R_{\mathrm{b}}$=$0.937\pm 0.042$~${\mathrm{R}}_{\mathrm{Jup}}$ and mass of $M_{\mathrm{b}}$=$36.50\pm 0.09$~${\mathrm{M}}_{\mathrm{Jup}}$, yielding a mean density of $59.0\pm 8.1$~$\mathrm{g}\mathrm{c}{\mathrm{m}}^{-3}$. The host star is nearly a Solar twin with mass $M_{\star }$=$0.99\pm 0.05$~${\mathrm{M}}_{\odot }$, radius $R_{\star }$=$1.01\pm 0.04$~${\mathrm{R}}_{\odot }$, effective temperature ${\mathrm{T}}_{\mathrm{eff}}$=$5850\pm 85$~K and iron abundance [Fe/H]=$0.03\pm 0.08$~dex. Its age, spectroscopic distance, and reddening are consistent with those of Ruprecht-147, corroborating its cluster membership. EPIC 219388192 b is the first brown dwarf with precise determinations of mass, radius and age, and serves as benchmark for evolutionary models in the sub-stellar regime.

arXiv comment13 pages, 11 figures, 4 tables, submitted to AAS Journals

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