Infrared spectroscopy of faint high Galactic latitude carbon stars

Carbon stars at high Galactic latitudes used to study the kinematics of the Galactic halo are difficult to distinguish from nearby dwarf carbon (dC) stars at intermediate spectral resolution. This paper presents near-infrared spectra of a sample of carbon stars that show that the CO first-overtone bands are far weaker in the known dC stars than in giants for a given H-K color. This finding, along with the unusual location of dC stars in the JHK color-color diagram, may be explained by the effects of collision-induced absorption, which is predicted, in stars of low metallicity and high surface gravity, to greatly suppress molecular absorption features in the near-infrared.