Infra-red Photometry of R Coronae Borealis Type Variables and Related Objects

Abstract

Infra-red photometry ( J, H, K, L ) is given for 12 RGB stars, three HdC stars and two helium stars. N, Q observations are given for six of the RCB stars. Most of the RCB stars show infra-red excesses. Although the HdC and helium stars are related spectroscopically to the RCB stars they do not show IR excesses. Evidently the occurrence of an IR excess is intimately connected with the RCB phenomenon rather than being a general property of hydrogen deficient, carbon-rich objects. This is understandable if the circumstellar shell is periodically replenished by particles ejected by the variables at minimum. The very hot RCB star, MV Sgr has an IR excess which indicates a hotter shell (1200°–1500°) than that found in other RCB stars (800°–900°). V348 Sgr, a peculiar carbon-rich hydrogen-poor variable, has a large infra-red excess. This strengthens its similarity to the RCB stars. Recently proposed models for the RCB phenomenon are considered. Ejection of particles at minima rather than geometrical eclipses by circumstellar dust blotches seems required by the observations.