RV Tauri
Two distinct types of Cepheid variable have been identified, which have different period-luminosity relationships: Classical Cepheid variables are young massive population I stars; type II Cepheids are older population II stars with low masses, including W Virginis variables, BL Herculis variables and RV Tauri variables. The Classical Cepheids are more luminous than the type II Cepheids with the same period.