2009MNRAS.395.1591D

We report the identification, from a photometric, astrometric and spectroscopic study, of a massive white dwarf member of the nearby, approximately solar metallicity, Coma Berenices open star cluster (Melotte111). We find the optical to near-infrared energy distribution of WD1216+260 to be entirely consistent with that of an isolated DA and determine the effective temperature and surface gravity of this object to be T_eff= 15739⁺¹⁹⁷_–196 K and logg = 8.46^+0.03_–0.02. We set tight limits on the mass of a putative cool companion, M ≳ 0.036M_☉(spatially unresolved) and M ≳ 0.034M_☉(spatially resolved and a ≲ 2500au). Based on the predictions of CO core, thick H layer evolutionary models we determine the mass and cooling time of WD1216+260 to be M_WD= 0.90±0.04M_☉ and τ_cool= 363⁺⁴⁶_–41Myr, respectively. For an adopted cluster age of τ = 500±100Myr we infer the mass of its progenitor star to be M_init= 4.77^+5.37_–0.97M_☉. We briefly discuss this result in the context of the form of the stellar initial mass-final mass relation.