A spectroscopic study of bright southern Cepheids - a high-resolution view of Cepheid atmospheres

We present high-resolution spectroscopic observations and species-by-species radial velocities of a number of southern Cepheids. The stars (BP Cir, V350 Sgr, AX Cir, V636 Sco, W Sgr, S Mus, β Dor, TT Aql, Y Oph, YZ Car, SW Vel, X Pup, T Mon and l Car) were observed as part of a long-term programme at Mt John University Observatory. Radial velocities were determined with the line bisector technique, and have a precision of ∼300 m s−1. Velocity differences as large as 30 km s−1 were found for Hα and Ca ii when referenced to the metallic line velocity curves, but more subtle variations (of 1–2 km s−1) were also detected in many other species. Pulsational phase anticorrelations are found between lines of Si ii and Ba ii, confirming the propagation time delay between line-forming layers producing these two species. We find that the amplitude and phase differences between the various species increase with period.