Absolute magnitudes of carbon stars from Hipparcos parallaxes

Hipparcos trigonometric parallaxes and photometric data for about 40 bright carbon stars have been analysed. Individual absolute visual and bolometric magnitudes, normal color indices (B - V)₀, absorption values and distance moduli were determined. By comparison with stellar evolutionary tracks for initial mass 1 ≤; M/M_⊙ ≤ 4 it is found that the majority of CH- and R-stars are on the giant and subgiant branches, but N-stars occupy a region -4 < M_V < -1 and 1.6 < (B - V)₀ < 3.6 and correspond to an advanced stage of thermally pulsing asymptotic branch giants. Previous absolute magnitude estimates, especially those from statistical parallaxes, are confirmed by Hipparcos. Using Hipparcos parallaxes and proper motions, three multiple stars with a carbon star component are examined. Hipparcos data confirms a physical link between W CMa and HD 54306 (B2V), both probable members of the association CMa OB1. Some stars are located below the subgiant branch for the mass 1M_⊙ and a number of the N stars are below the theoretical limit for carbon stars on the AGB.