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J. A. Munn, H. C. Harris (USNO, Flagstaff Station)
We combine SDSS photometry and astrometry with USNO-B astrometry to create an improved proper motion catalog, complete to g < 20, over the entire sky scanned by SDSS (ultimately approximately 8000 square degrees). USNO-B astrometry is recalibrated against SDSS, yielding improved proper motions with errors of order 3 mas/year. The proper motions are combined with the accurate SDSS photometry to create reduced proper motion diagrams, from which a well defined sample of white dwarfs is selected. Reduced proper motions are a particularly effective way for selecting cool white dwarfs, whose colors are similar to those of main sequence stars and thus difficult to select based on photometry alone, as well as halo white dwarfs. The cool end of the white dwarf luminosity function is currently poorly constrained, yet is vital for determining the age and star formation history of the Galactic disk. The sample of white dwarfs selected in this way from the final SDSS catalog will enable the construction of luminosity functions for both disk and halo white dwarfs using samples considerably larger than have previously been used. A program of spectroscopic confirmation of subsamples of the white dwarf candidates is currently underway.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.