The Mass and Radius of 40 Eridani B from [ITAL]HIPPARCOS[/ITAL]: An Accurate Test of Stellar Interior Theory

The astrometric satellite HIPPARCOS has determined the distance to the important white dwarf 40 Eridani B with an accuracy surpassing 1%. We use this datum to redetermine the mass and radius of this star and find that M = 0.501 ± 0.011 M☉ and R = 0.0136 ± 0.00024 R☉. These values, the most accurately determined masses and radii for any white dwarf star, place 40 Eri B securely on the zero-temperature carbon core mass-radius relation, considerably improving observational confirmation of the theory of stellar degeneracy. The mass is now sufficiently high that binary star evolutionary channels are no longer required to account for it. The data exclude the possibility that the surface hydrogen layer is as thick as 10-4 M☉.