AAS 201st Meeting, January, 2003
Session 33. Stars Dead or Alive
Oral, Monday, January 6, 2003, 2:00-3:30pm, 606-607

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[33.03D] Observations of white dwarfs in open clusters: the initial-final mass relation and the "white dwarf deficit"

K.A. Williams (UC, Santa Cruz), M. Bolte (UCO/Lick Obs.)

We present the first results from a photometric and spectroscopic investigation of white dwarfs (WDs) in intermediate-age open clusters ( 8M\odot \gtrsim MMSTO \gtrsim 3M\odot). Deep UBV photometry of several open clusters results in catalogues of candidate WDs in each cluster.

High signal-to-noise spectra have been taken of the WD candidates in three open clusters: IC 4665, NGC 6633, and NGC 7063. The rate of success in finding WDs is ~67%, with non-WDs identified as hot subdwarf stars and QSOs. By fitting spectra to model atmospheres, the Teff and log g for each WD was determined, from which the WD's mass and cooling age are inferred. Comparison with the photometry permits separation of cluster WDs from background and foreground field WDs. From the cluster WDs, an empirical initial-final mass relation is derived.

The WD catalogues contain many fewer WDs than would be expected in each cluster based on the observed number of main-sequence cluster members. This "white dwarf deficit" persists even after careful consideration of sample completeness and allowances for WDs in multiple-star systems and dynamical evolution of the cluster have been made. We explore the possibility that the maximum mass of white dwarf progenitors is lower than the commonly-stated 8M\odot. The implications of such a result could include an increase in the expected rate of core-collapse supernovae and challenges to existing models of the final stages in stellar evolution for stars with progenitor masses between 6M\odot and 8 M\odot.

We also report on the discovery of a potential helium-core WD in the open cluster NGC 7063. The age of the WD as derived from recent models is ~ 200Myr, in disagreement with the cluster age of 100 Myr.

The author(s) of this abstract have provided an email address for comments about the abstract: williams@ucolick.org

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.