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B. Margon (STScI)
In the past ten years it has been realized that dwarf carbon (dC) stars, objects with prominent molecular carbon bands in their spectra, but luminosity at or near the main sequence, are remarkably common. (Even the term ``dwarf carbon star" should be an oxymoron, as there should be no way for carbon to reach the surface until post-main sequence evolution). The initial lonely example of a dC, G77-61, has in the past decade been joined by about a dozen other similar stars discovered by heterogeneous techniques. All of these stars lie within about 100 pc, a volume containing not a single known giant C star. Therefore, the conclusion seems inescapable that, contrary to the assumptions of one hundred years of astronomical spectroscopy, the numerical majority of stars with molecular C in their spectra are in fact dwarfs, not giants.
Until now there has been no easy method of empirically verifying this surprising inference. However, recently the Sloan Digital Sky Survey (SDSS) has demonstrated its ability to successfully select faint C stars based on five color photometry, and verified spectroscopically: Margon et al. (AJ, 124, 1651, 2002) present several dozen newly discovered objects with 16 < R < 20. Based on the detection of proper motions in many of those stars, the majority of that still modest sample are inferred to be dwarfs. The SDSS faint C star sample has now grown to several hundred objects, a large enough group that interesting statistical inferences are finally possible. We discuss some properties of these rare stars. We now have direct evidence of the triumph of the dwarfs: the dC stars in the Galaxy most definitely outnumber the giants by a large factor.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.