HST Observations of Carbon and Hydrogen in DB White Dwarfs

Abstract

The differences in the structure of DA and DB white dwarfs hinge on the asteroseismological analysis of GD 358. However, spectroscopic investigation of this important white dwarf found spectral peculiarities, notably a very low hydrogen abundance and the presence of carbon. These results initiated further investigation of chemical composition of DB stars with intention to estimate the uniqueness of GD 358 and to test theories of white dwarf evolution and structure. Here we present HST spectroscopic observations of the DBs GD 190 and PG 0112.