Ultraviolet and Visual Spectroscopy of DB White Dwarfs

Abstract

Visual wavelength and IUE ultraviolet spectroscopy and model atmospheres of DB white dwarfs are reported. A search for spectral lines due to elements other than helium, and in particular carbon and hydrogen, was made. In no case is there a positive detection of carbon from these data, and upper limits relative to helium by number are derived in the range of C:He < 10^-5 to 10^-7 for the 15 DB stars with ultraviolet spectra in the temperature range 11,000K < T_eff< 23,000K. Additional new DBA stars are reported. Weak hydrogen Balmer lines are observed in the spectra of five of the 27 objects.