The Structure of White-Dwarf Atmospheres. II. Masses and Radii Determined from Atmospheric Parameters of DA Stars

A grid of model atmospheres for DA stars has been constructed by taking into account the blanketing effect of Balmer and Lyman lines, and effective temperatures and surface gravities are determined by comparing the observed color indices with those predicted by the models. The effect of line blanketing on the temperature stratification is such that the (U - B, B - V)-diagram predicts effective temperatures which are about 10 per cent lower than the values obtained in Paper I from models without blanketing, while no significant change is found in the surface gravities. Instead, a careful treatment of Balmer-line blocking for the computation of the emergent flux, using a more accurate Stark profile, leads to an in- crease of about 0.7 in log g. The masses and radii determined for thirty DA stars for which the luminosities are known are compared with the theoretical mass-radius relations for zero-temperature degenerate stars composed of heavy elements, and possible causes of the large discrepancies shown by the stars are dis- cussed