Sirius B mass and radius in solar units compared to the mass-radius relation for carbon-core white dwarfs. The two ellipsoidal contours are the 1s and 2s regions determined by Holberg et al. (1998). The vertical stippled region is the range of the astrometric mass determined by Gatewood & Gatewood (1978) while the heavy trapezoid is the joint 1s spectroscopic and astrometric estimate of Holberg et al. (1998). The sloping black curve is the theoretical mass-radius relation for a ∼25 000 K DA white dwarf with a C–O core (Wood 1995). The upper error bars are those corresponding to the G750M measurement with the mass derived from the surface gravity on the left and that from the gravitational redshift on the right [dark grey (blue on-line) and mid-grey (red) crosses, respectively]. The lower pair of error bars [light grey (green) and mid-grey (purple)] are the corresponding mass determinations for the lower radius obtained from the G430L results.