Abstract
We present new high resolution profiles of Ha emissions in radially pulsating stars (RR Lyrae, W Virginis, RV Tauri, Mira stars and Classical Cepheids). Depending on phase, these profiles can show an apparent absorption within the emission close to the Hα laboratory wavelength. The origin of this feature is discussed in the framework : (a) of a composite of a single emission and a deep photospheric absorption (RR Lyrae, W Virginis and RV Tauri stars); (b) of a true absorption caused by cool hydrogen above the shock wave producing the emission; (c) of a geometric model in which the absorption is a lack of emission. Recent observations (Hα profiles of Mira stars S Car and T Cen), which show that the absorption dip is below the continuum level, are in favour of the true absorption model.
Publisher
Cambridge University Press (CUP)