Computer Science
Scientific paper
Jul 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005hst..prop10634v&link_type=abstract
HST Proposal ID #10634
Computer Science
Hst Proposal Id #10634 Hot Stars
Scientific paper
We know approximate ages for the Galactic disk from white dwarf cooling theory applied to local white dwarfs and for the Galactic halo from main sequence stellar evolutionary theory applied to star clusters. However, the two chronometers are not cross-calibrated to the same absolute scale; our observations will perform this cross-calibration and improve the precision of both chronometers. We propose to use HST/ACS photometry of white dwarfs in five moderately old open cluster {0.6-2.2 Gyr}, along with all available up-to-date white dwarf interior and atmosphere models and a powerful new statistical approach, to compare main sequence evolutionary theory and white dwarf cooling theory. This comparison will be done in such a manner as to test white dwarf crystallization and carbon/oxygen phase separation, as well as main sequence models in the range where they are sensitive to the degree of core overshooting and where PP burning transitions to CNO burning. This confrontation is essential before we can accurately and precisely apply white dwarf cosmochronometry to the disk and halo field populations and to globular clusters. Past support by HST for white dwarf ages in globular clusters {123 orbits for M4 and a similarly large scheduled campaign for NGC 6397} will only be fully levereged by ensuring that both stellar chronometers are calibrated to the same age scale. Only then can white dwarf chronometers live up to their potential as fundamental, independent, and new age estimators for the Galaxy.
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