Events in Physics
Jay Holberg (University of Arizona)
Large Samples and Ground Truth: The 25 Parsec Local White Dwarf Population
J. B. Holberg
Lunar and Planetary Laboratory, University of Arizona, Tucson AZ
White dwarf stars are studied both as individual objects and as collective members of large surveys. The former emphasizes the unique aspects of the stars while the latter emphasizes population characteristics such as high proper motions or uv-excesses. Although large surveys enhance our statistical understanding of degenerate star populations (and turn up intriguing new object types) they are often too narrowly focused to simultaneously include all white dwarf classes. The enumeration of all white dwarfs within a limited volume of space offers the best opportunity for both the systematic and detailed study of individual stars, and at the same time realizing a significantly large sample size. Such a volume-limited study achieves very high levels of completeness and permits drawing inferences that can be related directly to larger surveys.
We have extended the detailed survey of the local white dwarf population from 20 pc to 25 pc, effectively doubling the sample volume. The present 25 pc sample contains 226 white dwarf stars having an estimated completeness of 70% (the corresponding 20 pc sub-sample is now 85% complete). The space density of white dwarfs remains at 4.8 ± 0.5 x 10-3 pc-3. We have also produced a white dwarf mass distribution and luminosity function based on the 25 pc sample. A discussion of likely sources for likely new members of the local sample is provided.