A massive white dwarf member of the Coma Berenices open cluster

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 (Melotte 111). We find the optical to near-infrared energy distribution of WD 1216+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[Subscript:eff]= 15 739[Superscript:+197][Subscript:−196] K and log g= 8.46[Superscript:+0.03][Subscript:−0.02]. We set tight limits on the mass of a putative cool companion, M≳ 0.036 M[Subscript:⊙] (spatially unresolved) and M≳ 0.034 M[Subscript:⊙] (spatially resolved and a≲ 2500 au). Based on the predictions of CO core, thick H layer evolutionary models we determine the mass and cooling time of WD 1216+260 to be M[Subscript:WD]= 0.90 ± 0.04 M[Subscript:⊙] and τ[Subscript:cool]= 363[Superscript:+46][Subscript:−41] Myr, respectively. For an adopted cluster age of τ= 500 ± 100 Myr we infer the mass of its progenitor star to be M[Subscript:init]= 4.77[Superscript:+5.37][Subscript:−0.97] M[Subscript:⊙]. We briefly discuss this result in the context of the form of the stellar initial mass–final mass relation.