RV Tauri stars -- II. A spectroscopic study

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Abstract
A long-term photometric and spectroscopic survey of eleven RV Tauri stars has been undertaken with a view to obtaining a better understanding of the nature of these pulsating variables. Pollard et al. presented the results from the long-term multicolour photometric survey. This paper presents the contemporaneous moderate- to high-resolution spectroscopy 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 is consistent with the few previous high-resolution spectroscopic studies of the three brightest RV Tauri stars: R Sct, U Mon and AC Her. Specifically, the Hα profiles exhibit two enhancements of emission per cycle following the passage of the primary and secondary shock waves through the photosphere around phases 0.1 and 0.6. Metallic lines showed ‘doubled’ profiles characteristic of an atmospheric shock wave around these phases, with evidence of two radial velocity cycles per formal period. In the RVb-type stars, an additional contribution to the Ha emission is seen and this appears to be correlated with the long-term period. Two stars, AI Sco and IW Car, display extended blueward Ha absorption which may arise from mass outflow. Evidence of long-term radial velocity variations is also seen in a number of the RVb stars.

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