Masses and radii of white-dwarf stars. IV. The two-color diagram.

Newly calculated model atmospheres, including both the effects of Lyman and Balmer line blanketing and the effects of convection, are used to determine the surface gravities of white-dwarf stars by the use of the separation of stars with different surface gravities in the Stromgren and multichannel two-color diagrams. Comparison of all available investigations of white-dwarf masses shows that they are internally consistent with the possible exception of masses derived from gravitational redshifts, where a slight, marginally significant discrepancy may exist. The weighted mean of all mass determinations is 0.75 solar mass, allowing for selection effects. The 1 sigma range of white-dwarf masses extends from 0.5 solar mass to 1.0 solar mass; no evidence is found for a smaller mass range.