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 _ { 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 \mathrel { \hbox { \raise 2.15 pt \hbox { $ > $ } \hbox to 0.0 pt { \lower 2.15 pt \hbox { $ \sim$% } } } } 0.036M _ { \odot } ( spatially unresolved ) and M \mathrel { \hbox { \raise 2.15 pt \hbox { $ > $ } \hbox to 0.0 pt { \lower 2.15 pt \hbox { $ \sim$% } } } } 0.034M _ { \odot } , ( spatially resolved and a \mathrel { \hbox { \raise 2.15 pt \hbox { $ < $ } \hbox to 0.0 pt { \lower 2.15 pt \hbox { $ \sim$% } } } } 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 \pm 0.04 M _ { \odot } and \tau _ { 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 _ { 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 .