RV TAURI STARS .2. A SPECTROSCOPIC STUDY

A long-term photometric and spectroscopic survey of eleven RV Tauri st ars has been undertaken with a view to obtaining a better understandin g of the nature of these pulsating variables, Pollard et al, presented the results from the long-term multicolour photometric survey. This p aper presents the contemporaneous moderate- to high-resolution spectro scopy of these stars. All the RV Tauri stars in our sample display, or are consistent with, two shock waves propagating in their atmospheres per 'formal' period (the time between successive deep minima). This i s consistent with the few previous high-resolution spectroscopic studi es of the three brightest RV Tauri stars: R Sct, U Mon and AC Her. Spe cifically, the H alpha profiles exhibit two enhancements of emission p er cycle following the passage of the primary and secondary shock wave s through the photosphere around phases 0.1 and 0.6. Metallic lines sh owed 'doubled' profiles characteristic of an atmospheric shock wave ar ound these phases, with evidence of two radial velocity cycles per for mal period. In the RVb-type stars, an additional contribution to the H alpha emission is seen and this appears to be correlated with the lon g-term period. Two stars, AI Sco and IW Car, display extended blueward H alpha absorption which may arise from mass outflow. Evidence of lon g-term radial velocity variations is also seen in a number of the RVb stars.