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K. B. Halford, G.R. Knapp (Princeton), H.C. Harris (USNO), D.J. Schlegel (LBNL), P.B. Hall (York U.), J.E. Gunn, M.A. Strauss, R.H. Lupton (Princeton)
The SDSS has, to date, spectroscopically confirmed 170 DQ white dwarfs (cool WDs showing spectral features of atomic and molecular carbon). Because of the effect of strong Swan band absorption on the SDSS g magnitude, DQWDs of temperatures about 5,000 - 8,000 K overlap in color with low-redshift quasars, and a complete spectroscopic sample can be identified, allowing the space density of these stars to be measured. We describe the implications for the WD cooling sequence and the age of the local Galactic disk. The properties of the objects in this large sample support previous findings (Dufour et al. 2005, ApJ 627, 404) of a small number of DQWDs with anomalously deep Swan band absorption and the possible transition below T(eff) = 6000 K to "C2H" WDs. We also find DQWDs with unusual properties including several stars with H Balmer-line absorption and a possible metal-rich DQWD.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.