RV Tauri variable

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RV Tauri variables are supergiant variable stars. They exhibit changes in luminosity which are tied to radial pulsations of their surfaces. Their changes in brightness are also correlated with changes in their spectral type. While at their brightest, the stars have spectral types F or G. At their dimmest, their spectral types change to K or M. The formal period of brightness fluctuations is typically around 30 to 150 days, and exhibits alternating primary and secondary minima, which can change relative to each other. Difference between maximum and minimum brightness can be as much as four magnitudes. RV Tauri stars are further subclassified into two types:

RVa variables: these are RV Tauri variables which do not vary in mean brightness
RVb variables: these are RV Tauri variables which show periodic variations in their mean brightness, so that their maxima and minima change on 600 to 1500 day timescales

The prototype of these variables, RV Tauri is a RVb type variable which exhibits brightness variations between magnitudes +9.8 and +13.3 with a formal period of 78.7 days.

RV Tauri stars may be post-AGB objects. They are thought to be mostly binaries with dust possibly confined to a disc. [1]