Metallic-line and Hα radial velocities of seven southern Cepheids: a comparative analysis

New metallic-line and Hα velocity curves have been produced for seven southern Cepheids. A comprehensive comparison is made between these data and those of previous observers and also with other Cepheids having similar periods. Use is made of the line bisector method to derive the velocity information and also to investigate asymmetries in the Hα lines. These bisectors provide a consistent approach to the analysis of spectroscopic data of Cepheids and will enable more quantitative studies of the structure of Cepheid atmospheres. This will in turn enable more reliable radii and hence distances to be deduced and a better use of Cepheids to establish the distances to nearby galaxies.