SIMBAD references

We studied the class of DB white dwarf stars, using re-calibrated UV spectra for thirty four DBs obtained with the IUE satellite. By comparing the observed energy distributions with model atmospheres, we simultaneously determine spectroscopic distances (d), effective temperature (T_eff), and surface gravities (logg). Using parallax measurements and previous determinations of T_eff and logg from optical spectra, we can study whether the atmospheres of eleven DB stars are consistent with pure He or have a small amount of H contamination. We also report on our observations of seventeen stars with T_eff close to the DB instability strip through time series photometry and found them to be non variable within our detection limits.