The distance, temperature, and luminosity of the hypergiant P Cygni (B1 Ia+).

Abstract

The basic parameters of P Cyg (B1 Ia+) are determined from a study of the overall energy distribution from 1150 A to 6 cm. The color excess of E(B-V) = 0.63 + or - 0.05 is derived from the strength of the interstellar Lyman-alpha line, from the spectral type, and from a comparison of the UV energy distribution with those of other supergiants. The intrinsic energy distribution does not agree with the predictions from plane-parallel line blanketed models, in that the UV flux is smaller than predicted compared to the visual flux. The available information about the distance of the star and its cluster membership results in an estimate of d = 1.8 + or 0.1 kpc. From the energy distribution and the distance the following basic parameters are derived: T(eff) = 19,300 + or 2000 K, R = 76 + or - 14 solar radii, M(v) = - 8.3 + or - 0.3, M(b) = - 9.9 + or - 0.8. The mass of the star is estimated to be 30 + or - 10 solar masses, if the star is in the helium core burning phase.