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Session 18 - White Dwarfs.
Display session, Monday, January 15
North Banquet Hall, Convention Center
We present a preliminary determination of the luminosity function of spectroscopically identified white dwarfs in common proper motion binaries. We use a novel approach to correct our observed sample for incompleteness to \mu \ge 0\farcs15/yr and \mpg \le +18.4, new model atmosphere results to provide bolometric corrections, and improved white dwarf evolutionary models to construct theoretical luminosity functions which are compared to our observations. Our results suggest that white dwarfs are more commonly found as components of wide binaries than as single stars. They also indicate that star formation most likely commenced in the solar neighborhood \approx 11^+4_-2 Gyr ago. We show in this paper that the observed downturn in the white dwarf luminosity function occurs at substantially lower luminosities than indicated by previous studies. Our results are consistent with the evolutionary history of the Galaxy suggested by estimates of globular cluster ages obtained by isochrone fits (\approx 14 to 18 Gyr). However, the minimum age for the Galaxy that we derive is more than 2\sigma older than the age of the Universe suggested by recent ground- and space-based determinations of the Hubble constant (\approx 8.3 Gyr, assuming standard inflationary cosmology).
The authors gratefully acknowledge support from NSF grants AST-9016284 (TDO) and AST-9217988 (MAW), NASA Graduate Student Research Fellowship NGT-51086 (JAS), NASA Astrophysics Theory Program Grant NAG 5-3103 (MAW), and an Ernest F. Fullam Award from the Dudley Observatory (MAW amp; TDO).
Program listing for Monday