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

A grid of synthetic line profiles incorporating a new treatment of mac roturbulence 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 ob servations of Cepheids has been carried out at Mt John University Obse rvatory for several years. Radial velocities and asymmetries have been measured for selected metallic lines and the asymmetries compared wit h those of the synthetic profiles. The line profiles from the observat ions show a larger asymmetry than the synthetic profiles at phases of inward pulsational velocity. The asymmetry at phases of outward veloci ty is smaller and in agreement with the synthetic profiles for some Ce pheids. For others, however, the asymmetry at phases of outward pulsat ion is in the direction expected for inward motion. The discrepant lin e asymmetries cannot be due to geometric projection of a single pulsat ional velocity, an assumption inherent in calculations of radii and di stances by the Baade-Wesselink method.