SIMBAD references

We present a comprehensive analysis of the far-ultraviolet spectra of three DB white dwarfs secured with the FUSE observatory. Transitions associated with various carbon ions are detected in all three objects. Atmospheric parameters are first redetermined on the basis of an analysis of archival data available, and the abundance of carbon, together with upper limits on the abundances of 11 other heavy elements, is determined from the FUSE spectra. The log(C/He) ratios cover the range between -5.5 and -6.0. The presence of carbon, now detected in five DB stars with effective temperatures above 20,000 K, cannot be accounted for easily by physical processes currently thought to operate in the envelopes of DB stars. We suggest that a weak stellar wind threading the outer stellar layers of DB stars might sufficiently disrupt the settling of carbon left over from the PG 1159 phase to account for the carbon seen in the ultraviolet spectra of these objects.