Rotationally Extended Stellar Envelopes—III: The Be Component of VV Cephei

Abstract

A new orbit is derived for the system of VV Cephei from recent observations. Emission line profiles of H α in the spectrum obtained during the 1956–58 eclipse are studied and the variation of width, height, equivalent width and velocity distortion presented as a function of phase. Various simplified calculations of the velocity and equivalent width are made and their inadequacy shown. A program is described for computing the H α profile at any orbital phase, and a model for the system and the Be envelope that gives the best fit to the observational quantities is derived. The Be envelope is large, rotating at the limit of stability in its inner layers and apparently accumulating matter from gas-streaming in its outer parts. The central star is probably a main sequence O8 star. Finally, out of eclipse light variations of 0 ^m. 1 or more are predicted for this system and 32 Cygni, by mutual distortion effects.