The continuing slow decline of AG Pegasi

We analyze optical and ultraviolet observations of the symbiotic binary AG Pegasi acquired during 1992-1997. The bolometric luminosity of the hot comp onent declined by a factor of 2-3 from 1980-1985 to 1997. Since 1992, the e ffective temperature of the hot component may have declined by 10%-20%, but this decline is comparable to the measurement errors. Optical observations of H beta and He I emission show a clear illumination effect, where high-e nergy photons from the hot component ionize the outer atmosphere of the red giant. Simple illumination models generally account for the magnitude of t he optical and ultraviolet emission-line fluxes. High-ionization emission l ines-[Ne V], [Mg V], and [Fe VII]-suggest mechanical heating in the outer p ortions of the photoionized red giant wind. This emission probably originat es in a low-density region similar to 30-300 AU from the central binary.