HOT BOUNDARY-LAYERS IN SYMBIOTIC BINARIES AX-PERSEI AND CI-CYGNI

Accretion disk boundary layer models are calculated for the symbiotic binaries AX Per and CI Cyg, using a time-dependent numerical code. Hot boundary layers are found with temperatures above 10(5) K, assuming f or the accreting star a mass M = 0.5 M. and a radius R* = 0.2 R.. How ever, choosing a larger stellar radius or a smaller stellar mass leads to cooler boundary layers. The numerical solutions agree fairly well with the observational estimates of the hot component temperature duri ng quiescence but do not reproduce the apparent drop in effective temp erature seen during the outburst of AX Per and CI Cyg. The maximum eff ective temperature obtained in the boundary layer solutions increases as the mass accretion rate increases (M = 1-10 x 10(-5) M. yr(-1)) but then stays nearly constant as the mass accretion rate approaches the Eddington limit (in the present case, M(Edd) approximate to 10(-4) M. yr(-1)). In this high accretion rate regime, the disk becomes geometri cally thick (H/r approximate to 0.4), and the energy dissipated in the dynamical boundary layer is radiated outward to larger radii and adve cted into the star. The boundary layer luminosity is only approximate to 2/3 its expected value; the rest of the energy is advected into the star.