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 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 $T_{\rm eff}$=$15739^{+197}_{-196}$K
and log $g$=$8.46^{+0.03}_{-0.02}$. 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$2500AU).
Based on the predictions of CO core, thick-H layer evolutionary models we
determine the mass and cooling time of WD1216+260 to be M$_{\rm WD}$=$0.90
\pm0.04$M$_{\odot}$ and $\tau$$_{\rm cool}$=$363^{+46}_{-41}$Myrs respectively.
For an adopted cluster age of $\tau$=500$\pm$100Myrs we infer the mass of its
progenitor star to be M$_{\rm init}$=$4.77^{+5.37}_{-0.97}$M$_{\odot}$. We
briefly discuss this result in the context of the form of the stellar initial
mass-final mass relation.
