LINE-PROFILES OF CEPHEID VARIABLES - PROJECTION FACTORS AND METALLIC LINE ASYMMETRIES

A grid of synthetic line profiles incorporating a new treatment of macroturbulence is calculated for a Cepheid atmosphere in radial motion. Projection factors are determined to be up to 10 per cent higher than previous calculations. A programme of high-resolution spectroscopic observations of Cepheids has been carried out at Mt John University Observatory for several years. Radial velocities and asymmetries have been measured for selected metallic lines and the asymmetries compared with those of the synthetic profiles. The line profiles from the observations show a larger asymmetry than the synthetic profiles at phases of inward pulsational velocity. The asymmetry at phases of outward velocity is smaller and in agreement with the synthetic profiles for some Cepheids. For others, however, the asymmetry at phases of outward pulsation is in the direction expected for inward motion. The discrepant line asymmetries cannot be due to geometric projection of a single pulsational velocity, an assumption inherent in calculations of radii and distances by the Baade-Wesselink method.