PHOTOSPHERIC AND CHROMOSPHERIC ACTIVITY IN THE LATE-TYPE GIANT COMPONENT OF THE EVOLVED BINARY-SYSTEM HD-185510

UBV photometry and moderate resolution H alpha spectrophotometry of th e evolved binary system HD 185510 (sdB + KO III), performed at Catania Astrophysical Observatory, is presented and discussed. The spectropho tometric data were collected in 1991, 1993, and 1994, while the photom etric light curves were obtained in 1993, 1994 and 1995. From the B an d V photometry we determine a new photometric rotational period of 26( d).23, confirming the asynchronous rotation of the cool giant componen t. The spectroscopic data confirm the v sin i value of 15 Km s(-1) mea sured by Fekel et al. (1993) and clearly reveal a filled-in H alpha li ne with appreciable variations. The excess emission of the line, obser ved at any orbital phase, is found to be anticorrelated with the V lig ht curve and is primarily ascribed to the chromospheric activity on th e cool star. The primary total eclipse is clearly visible in the U ban d, but undetectable in the V band. From the U observations we determin ed a total duration of the primary eclipse (from 1(st) to 4(rd) contac t) of 1(d).3883, with the ingress lasting only 27 minutes. This new ac curate monitoring acid timing of the eclipse allowed us to improve the system solution which leads to R-C = 8.8 R., T-C = 4800 K, R-H = 0.11 R., T-H = 30 000 K for the cool and hot star respectively. The evolut ion of HD185510B is discussed also in relation to the evolutionary sta tus of HD 185510A and the synchronization time scale. HD 185510B is pr obably a sdB near the zero age extended horizontal branch, resulting f rom an enhanced mass loss in late case B or case A mass exchange with a possible common envelope phase. A small amount (15-20%) of mass loss from the system which can account for the strong IR excess is suggest ed.