A massive white dwarf member of the Coma Berenices Open Cluster

Abstract

We report the identification, from a photometric, astrometric and spectroscopic study, of a massive white dwarf member of the nearby, approximately solar metalicity, Coma Berenices open star cluster (Melotte 111). We find the optical to near-IR 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 $T_{\mathrm{eff}}$=$15739_{-196}^{+197}$K and log $g$=$8.46_{-0.02}^{+0.03}$. We set tight limits on the mass of a putative cool companion, M$\simgreat$0.036M${}_{\odot }$ (spatially unresolved) and M$\simgreat$0.034M${}_{\odot }$, (spatially resolved and a$\simless$2500AU). Based on the predictions of CO core, thick-H layer evolutionary models we determine the mass and cooling time of WD1216+260 to be M${}_{\mathrm{WD}}$=$0.90\pm 0.04$M${}_{\odot }$ and $\tau$${}_{\mathrm{cool}}$=$363_{-41}^{+46}$Myrs respectively. For an adopted cluster age of $\tau$=500$\pm$100Myrs we infer the mass of its progenitor star to be M${}_{\mathrm{init}}$=$4.77_{-0.97}^{+5.37}$M${}_{\odot }$. We briefly discuss this result in the context of the form of the stellar initial mass-final mass relation.

accepted for publication in MNRAS

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