A study of R Coronae Borealis and RV Tauri stars

A variety of aspects of R Coronae Borealis and RV Tauri variables are investigated. Simultaneous optical and infrared observations of both types of star allow stellar and dust shell parameters to be inferred. For R Coronae Borealis stars, light is thrown on mass loss mechanisms via statistical and model studies of deep minima. The R Coronae Borealis variables in the Large Magellanic Cloud are contrasted with their Galactic counterparts, in order to determine the interaction of these stars with their environment. IUE observations are used for this purpose. With optical and infrared data, IUE fluxes also allow the accurate calculation of the effective temperatures and angular radii of several of these stars. The charge on dust grains in the consequent circumstellar shells is calculated and its effects considered. In appendices, observations of the T Tauri star RY Lup and the dwarf nova Z Cha are discussed. (author)