On the radial distribution of white dwarfs in the globular cluster NGC 6397⋆

Abstract We have examined the radial distribution of white dwarfs over a single Hubble Space Telescope/Advanced Camera for Surveys field in the nearby globular cluster NGC 6397. In relaxed populations, such as in a globular cluster, stellar velocity dispersion, and hence radial distribution, is directly dependent on stellar masses. The progenitors of very young cluster white dwarfs had a mass of ∼0.8 M⊙, while the white dwarfs themselves have a mass of ∼0.5 M⊙. We thus expect young white dwarfs to have a concentrated radial distribution (like that of their progenitors) that becomes more extended over several relaxation times to mimic that of ∼0.5-M⊙ main-sequence stars. However, we observe young white dwarfs to have a significantly extended radial distribution compared both with the most massive main-sequence stars in the cluster and with old white dwarfs.