CIRCUMSTELLAR MATERIAL AND THE LIGHT VARIATIONS OF RV TAURI STARS

Infrared photometry on the JHKL system is given for 35 stars of the RV Tauri and related types. The RV Tauri stars show infrared excesses indicating the presence of circumstellar dust with a temperature of about 900 K. These dust shells can be equally prominent in oxygen-rich or carbon-rich stars; the high carbon content of the latter appears to counteract the inhibiting effect of their generally lower metal abundance in promoting dust formation. The wide range of energy distributions of RV Tauri stars is attributed in part to differences in the radial distribution of dust. The RVb stars (whose mean light varies cyclically) are redder than the RVa stars (which have constant mean light), indicating that their dust shells are denser especially in the inner regions, which radiate strongly in the 1-3 μm band. Far-infrared data reveal cooler dust around some of the stars of group a. Three W Virginis stars, two of which were already known to show affinities to the RV Tauri stars, have dust shells. The dust shells for which IRAS infrared spectra are available show the 10-μm silicate emission feature regardless of whether the optical spectra are carbon- or oxygen-rich. Some considerations regarding possible models are given. A comparison with the R Coronae Borealis variables has revealed similarities. © 1985 Royal Astronomical Society.