  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 (Teff), and surface
gravities (log g). Using parallax measurements and previous determinations of
Teff and log g 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 Teff
close to the DB instability strip through time series photometry and found them
to be non variable within our detection limits.
