CARBON STAR LUMINOSITY INDICATORS

Except for one odd dwarf, G77-61, it has long been assumed that carbon (C) stars are always giants, as carbon is thought to reach the photosphere only during dredge-up in asymptotic giant branch stars. However, we recently confirmed the existence of high proper motions in three other faint C stars (Green et al.). These three C stars are thus also inferred to be dwarfs. Not all dwarf C stars will have detectable proper motions, so other luminosity/distance indicators are needed. All four C dwarfs have similar JHK colors, suggesting IR colors as a possible luminosity indicator. We also find an unusually strong lambda6191 bandhead of carbon in our spectra of the dwarf C stars known to date. We present results of a proper motion survey of known faint high-latitude C stars using plates spanning a 30 yr baseline that reveals at least one additional new dwarf C star and also confirms the utility of our proposed luminosity indicators. Kinematic simulations suggest that virtually all Population II C dwarfs will have detectable proper motions in a survey as sensitive as our own, and that to a limit of V almost-equal-to 18, at least 10% of faint high-latitude C stars are dwarfs. The local space density of dwarf C stars may thus substantially exceed that of luminous C stars.