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) observations and reprocessed IUE NEWSIPS data have produced a new, well-defined 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 the Sirius system of π = 037921 ± 000158 is used in conjunction with the above spectroscopic results and the previously published gravitational redshift to yield a mass of 0.984 ± 0.074 M_☉ and a radius of R = 0.0084 ± 0.00025R_☉ for the white dwarf. Combining these results 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 Sirius B are found to be consistent with the theoretical mass-radius relation for a carbon-core white dwarf. The EUVE spectrum is also used to determine a firm upper limit of He/H = 1.8 × 10^-5 for the helium mixing ratio in the photosphere of Sirius B. IUE echelle spectra of Sirius B provide an estimate of log N_{H I} = 17.72 ± 0.1 for the interstellar H I column to this star.