Astrometry and photometry for two dwarf carbon stars

Preliminary trigonometric parallaxes and BVI photometry are presented for t wo dwarf carbon stars, LP 765-18 (=LHS 1075) and LP 328-57 (=CLS 96). The d ata are combined with the literature values for a third dwarf carbon star, G77-61 (=LHS 1555). All three stars have very similar luminosities (9.6 < M -V < 10.0) and very similar broadband colors across the entire visual-to-ne ar-IR (BVIJHK) wavelength range. Their visual (BVI) colors differ from all known red dwarfs, subdwarfs, and white dwarfs. In the M-V versus V-I color- magnitude diagram, they are approximately 2 mag subluminous compared to nor mal disk dwarfs with solar-like metallicities, occupying a region also popu lated by O-rich subdwarfs with -1.5 < [M/H] < -1.0. The kinematics indicate that they are members of the Galactic spheroid population The subluminosit y of all three stars is due to an as yet unknown combination of (undoubtedl y low) metallicity, possibly enhanced helium abundance, and unusual line bl anketing in the bandpasses considered. The properties of the stars are comp ared with models for the production of dwarf carbon stars.