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.

A new detailed examination of white dwarfs in NGC3532 and NGC2287

We present the results of a photometric and spectroscopic study of the white dwarf candidate members of the intermediate age open clusters NGC3532 and NGC2287. Of the nine objects investigated, it is determined that six are probable members of the clusters, four in NGC3532 and two in NGC2287. For these six white dwarfs we use our estimates of their cooling times together with the cluster ages to constrain the lifetimes and masses of their progenitor stars. We examine the location of these objects in initial mass-final mass space and find that they now provide no evidence for substantial scatter in initial mass-final mass relation as suggested by previous investigations. Instead, we demonstrate that, when combined with current data from other solar metalicity open clusters and the Sirius binary system, they hint at an IFMR that is steeper in the initial mass range 3M$_{odot}$$simless$M$_{rm init}$$simless$4M$_{odot}$ than at progenitor masses immediately lower and higher than this. This form is generally consistent with the predictions of stellar evolutionary models and can aid population synthesis models in reproducing the relatively sharp drop observed at the high mass end of the main peak in the mass distribution of white dwarfs.