  A search of more than 3,000 square degrees of high latitude sky by the Sloan
Digital Sky Survey has yielded 251 faint high-latitude carbon stars (FHLCs),
the large majority previously uncataloged. We present homogeneous spectroscopy,
photometry, and astrometry for the sample. The objects lie in the 15.6 < r <
20.8 range, and exhibit a wide variety of apparent photospheric temperatures,
ranging from spectral types near M to as early as F. Proper motion measurements
for 222 of the objects show that at least 50%, and quite probably more than
60%, of these objects are actually low luminosity dwarf carbon (dC) stars, in
agreement with a variety of recent, more limited investigations which show that
such objects are the numerically dominant type of star with C_2 in the
spectrum. This SDSS homogeneous sample of ~110 dC stars now constitutes 90% of
all known carbon dwarfs, and will grow by another factor of 2-3 by the
completion of the Survey. As the spectra of the dC and the faint halo giant C
stars are very similar (at least at spectral resolution of 1,000) despite a
difference of 10 mag in luminosity, it is imperative that simple luminosity
discriminants other than proper motion be developed. We use our enlarged sample
of FHLCs to examine a variety of possible luminosity criteria, including many
previously suggested, and find that, with certain important caveats, JHK
photometry may segregate dwarfs and giants.

Astrophysics