MULTIWAVELENGTH OBSERVATIONS OF RV TAURI STARS .1. AC HERCULIS

We present ultraviolet, optical and infrared (including IRAS) observations of the RV Tauri star AC Her. IRAS LRS spectra suggest that the dust shell of AC Her may consist of both silicon carbide and silicates, and modelling of the optical-infrared flux distribution suggests the presence of at least two distinct dust shells, the larger of which may be the fossil AGB remnant. That AC Her may indeed be a post-AGB object is also suggested by the C-12/C-13 ratio. We suggest that AC Her is not only undergoing mass-loss currently, but that it also underwent a period of substantial mass-loss in the past. Furthermore, quantitative computations confirm a suggestion by Gehrz, that the optical and infrared (IR) light curves can be understood only if the circumstellar dust shell is powered by a star undergoing strong non-radial oscillations. The behaviour of the UV-optical flux distribution, and of the ultraviolet MgII doublet, is consistent with this conclusion.