Towards a precise white dwarf cooling age of a globular cluster

Abstract

AbstractThe white dwarf cooling age of a globular star cluster provides a potentially precise method of determining the ages of these ancient systems. This age-dating technique should be viewed as one distinct from that of turn-off ages, with a largely different set of input physics and problems. As such the ages produced by these two methods are complimentary and we seek convergent to the same value. In addition to deep photometry and astrometry of cluster stars, precise distances to the clusters and their reddenings are required. Theoretical models of both main sequence stars and cooling white dwarfs are also needed as well as the masses of the white dwarfs and an initial-final mass relationship. In this contribution I discuss a potentially precise approach to cluster distances via a geometric technique (comparing the internal proper motion dispersion of cluster stars with their radial velocity dispersion) and spectroscopically determined masses of M4 white dwarfs at the top of the cooling sequence. These latter data extend the initial-final mass relationship down to the lowest mass stars that are currently forming white dwarfs.