Abstract

Refining our knowledge of the white dwarf mass-radius relation with HST observations of Sirius-type binaries

Martin Barstow (University of Leicester)

(1) S.L. Casewell, (2) J.B. Holberg, (1) M.R. Burleigh and (3) H. Bond (1) University of Leicester, (2) University of Arizona, Tucson, (3) Penn State University.

The presence of a white dwarf in a resolved binary system, such as Sirius, provides an opportunity to combine dynamical information about the masses, from astrometry and spectroscopy, with a gravitational red-shift measurement and spectrophotometry of the white dwarf atmosphere to provide a test of theoretical mass-radius relations of unprecedented accuracy. We demonstrated this with the first Balmer line spectrum of Sirius B to be obtained free of contamination from the primary, with STIS on HST. However, we also found an unexplained discrepancy between the astrometric and gravitational red-shift mass determinations. With the recovery of STIS, we have been able to revisit our observations of Sirius B with an improved observation strategy designed to reduce systematic errors on the gravitational red-shift measurement. We report on the refined precision of the Sirius B mass-radius measurements and extend this technique to a larger sample of white dwarfs in resolved binaries. Together these data provide accurate mass and radius determinations capable of testing the theoretical mass-radius relation and distinguishing between possible structural models.

Mode of presentation: oral