A member of a class of pulsating variable stars. RV Tauri stars are supergiants of spectral types F, G or K, showing variations of up to four magnitudes, but with minima alternating between deeper and shallower ones. Their periods lie between 30 and 150 days. There is evidence that these stars are losing mass rapidly via a stellar wind and they may be the precursors of planetary nebulae. They have the characteristics of old, evolved stars, and some are found in globular clusters.