AS 501 - A NEW-TYPE OF SYMBIOTIC STAR WIT H A HIGHLY EVOLVED COOL COMPONENT

Results of long-term photometric (BVJHKLM) and spectrophotometric (0.4 -1.0 mu m) observations of the peculiar variable star AS 501 (V627 Cas ) are presented. This variable is shown to be a binary system that con sists of an M2 Ib post-AGE red giant with a pulsation period of P simi lar or equal to 466 days and an active hot component with an unusually blue B-V color index reaching 1(m). In the 1990s, a two-year dimming episode was observed in the cool component of AS 501 in the infrared, which was equivalent to a decrease in its bolometric luminosity by a f actor of similar to 1.4. The infrared excess in the wavelength range 1 -60 mu m can be fitted by the radiation of an optically thick [tau(1.2 5 mu m) = 1.4] dust silicate shell formed on a time scale of similar t o 3 x 10(3) years at weakening mass loss from this binary system, M(t) similar to t(0.7), where the time is measured from now to the past, O ver this time interval, the rate of mass loss in AS 501 decreased by a factor of similar to 100, and this binary system lost similar to 0.25 M. of its mass.