Ensemble Properties of the White Dwarf Population of the Old, Solar
  Metallicity Open Star Cluster Messier 67
  White dwarfs are excellent forensic tools for studying end-of-life issues
surrounding low- and intermediate-mass stars, and the old, solar-metallicity
open star cluster Messier 67 is a proven laboratory for the study of stellar
evolution for solar-type stars. In this paper, we present a detailed
spectroscopic study of brighter (M_g < 12.4) white dwarfs in Messier 67, and,
in combination with previously-published proper motion membership
determinations, we identify a clean, representative sample of cluster white
dwarfs, including 13 members with hydrogen-dominated atmospheres, at least one
of which is a candidate double degenerate, and 5 members with helium-dominated
atmospheres. Using this sample we test multiple predictions surrounding the
final stages of stellar evolution in solar type stars. In particular, the
stochasticity of the integrated mass lost by ~1.5 solar mass stars is less than
7% of the white dwarf remnant mass. We identify white dwarfs likely resulting
from binary evolution, including at least one blue straggler remnant and two
helium core white dwarfs. We observe no evidence of a significant population of
helium core white dwarfs formed by enhanced mass loss on the red giant branch
of the cluster. The distribution of white dwarf atmospheric compositions is
fully consistent with that in the field, limiting proposed mechanisms for the
suppression of helium atmosphere white dwarf formation in star clusters. In
short, the white dwarf population of Messier 67 is fully consistent with basic
predictions of single- and multiple-star stellar evolution theories for solar
metallicity stars.
