On the radial distribution of white dwarfs in the globular cluster NGC 6397
Anderson, J.; Davis, D. S.; King, I. R.; Kalirai, J. S.; Hurley, J.; Richer, H. B.; Fahlman, G. G.; Coffey, J.
Canada, United States, Australia
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 ~0.8Msolar, while the white dwarfs themselves have a mass of ~0.5Msolar. 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-Msolar 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.
Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with proposals GO-10424 and GO-8679. E-mail: sdavis@astro.ubc.ca (DSD); richer@astro.ubc.ca (HBR) ‡ Hubble Fellow.