RV Tauri

RV Tauri stars are luminous, long-period members of the type II class of Cepheid variables. The shorter period stars of the W Vir class are hydrogen and helium shell burning stars, while the RV Tauri stars are believed to be in a more advanced stage of evolution at the end of the asymptotic giant branch (AGB). As such, the structure of an RV Tauri star would be a C-O degenerate core with a thin overlying helium layer inside a large, tenuous, convective, hydrogen-rich envelope. Mixing of the two outer layers leads to enrichment of the photosphere with He-burning and s-process elements.