SIRIUS-B - A NEW, MORE ACCURATE VIEW

Long-standing questions regarding the temperature, gravity, mass, and radius of the well-known white dwarf Sirius B are considered in light of new data. Recently obtained Extreme Ultraviolet Explorer (EUVE) obs ervations and reprocessed IUE NEWSIPS data have produced a new, well-d efined effective temperature of 24,790 +/- 100 K and a surface gravity of log g = 8.57 +/- 0.06 for Sirius B. A new Hipparcos parallax for t he Sirius system of pi = 0.'' 37921 +/- 0.'' 00158 is used in conjunct ion with the above spectroscopic results and the previously published gravitational redshift to yield a mass of 0.984 +/- 0.074 M. and a rad ius of R = 0.0084 +/- 0.00025R. for the white dwarf Combining these re sults with the existing astrometric mass for Sirius B gives a refined mass estimate of M = 1.034 +/- 0.026 M.. The mass and radius for Siriu s B are found to be consistent with the theoretical mass-radius relati on for a carbon-core white dwarf. The EUVE spectrum is also used to de termine a firm upper limit of He/H = 1.8 x 10(-5) for the helium mixin g ratio in the photosphere of Sirius B. IUE echelle spectra of Sirius B provide an estimate of log N-HI = 17.72 +/- 0.1 for the interstellar H I column to this star.