The Evolutionary Status of SS 433.

We consider possible evolutionary models for SS 433. We assume that common envelope evolution is avoided if radiation pressure is able to expel most of a super-Eddington accretion flow from a region smaller than the accretor's Roche lobe. This condition is satisfied, at least initially, for largely radiative donors with masses in the range 4-12 M middle dot in circle. For donors more massive than about 5 M middle dot in circle, moderate mass ratios q=M2&solm0;M1 greater, similar1 are indicated, thus tending to favor black hole accretors. For lower mass donors, evolutionary considerations do not distinguish between a neutron star or black hole accretor. In all cases the mass transfer (and mass-loss) rates M&d2;tr approximately 7x10-6 to 4x10-4 M middle dot in circle yr-1 are much larger than the likely mass-loss rate M&d2;jet approximately 10-6 M middle dot in circle yr-1 in the precessing jets. Almost all of the transferred mass is expelled at radii considerably larger than the jet acceleration region, producing the "stationary" Halpha line and the infrared luminosity and accounting for the low X-ray luminosity.