Line asymmetry and projection factors in Cepheid variables

Abstract

New methods for displaying radial velocities of pulsating stars are presented. The profiles of weak spectral lines in Cepheids are observed to be asymmetric during the inward velocity part of the pulsation cycle but not the outward velocity part. A prescription is given for standardising the method of measuring radial velocity. New projection factors are calculated for Cepheid variables using this method and p=1.37 is recommended as a constant value. This should lead to a systematic error in radius determinations of ~1% from this source.