Empirical confirmation of the mass dependence for white dwarf luminosities

Abstract

Existing calibrations of white dwarf luminosities have invariably relied upon the inhomogeneous sample of refractor parallaxes published in the General Catalogue of Trigonometric Parallaxes. We have completed a new calibration of white dwarf absolute magnitudes using a compilation of homogeneous and very accurate reflector parallaxes published by the U.S. Naval Observatory. The properties of the stars in this sample are well enough established that statistical luminosity corrections resulting from the combination of parallax errors with the space distribution peculiar to the stars can be established fairly reliably. The resulting luminosity calibration is in very good agreement with previously published results, and is of sufficient accuracy to investigate for the subset of DA-type stars the expected dependence on surface gravity (or mass) predicted theoretically from the white dwarf mass-radius relation. The results are in complete accord with expected results, which indicates that a full knowledge of the luminosity for any DA-type white dwarf requires information on its surface gravity as well as effective temperature. A byproduct of this study is a new estimate for the distance to the Hyades cluster, which contains several member DA stars.