Discovery of a highly magnetic white dwarf with strong carbon features

Systematic follow-up of high proper-motion stars has identified a new cool magnetic white dwarf that displays a series of spectacular absorption bands in the range 4200-6500 Angstrom. The spectrum bears a striking resemblance to that of LP 790-29, a magnetic DQ star dominated by what are apparently Zeeman-shifted Swan bands of Ct. However, key differences in the detailed spectra, polarization, and temperature of the two stars indicate that instead LHS 2229 may represent the first case of a magnetic "peculiar" DQ white dwarf, where absorption in the optical is produced by C2H or another carbon-hydrogen compound. Crude arguments suggest that the field strength on LHS 2229 is in the neighborhood of 10(8) G. BVI photometry proves to be effective in identifying such peculiar stars, since they lie well outside the main white dwarf sequence in a color-color diagram.