Four-colour photometry of eclipsing binaries. XIa.

The previously published uvby light curves (Clausen and Nordström, 1978a) of the A-type double-lined eclipsing binary RS Cha have been analysed. Photometric elements are determined (Table 4) by means of the eclipsing binary model and the light curve simulation programme WINK described by Wood (1971, 1972). These photometric elements, combined with the spectroscopic data by Andersen (1975) yield the absolute dimensions given in Table 6. The chemical composition (Y, Z) = (0.28 ± 0.05, 0.02 ± 0.005) for the mean component of RS Cha is derived from the stellar model calculations by Hejlesen (unpublished extension of Hejlesen et al., 1972).

The observations show that at least one of the components is an intrinsic variable, probably of the δ Scu type, as suggested by Andersen (1975). We conclude that the variations should probably be ascribed to the secondary component.