SS 433: Observation of the circumbinary disk and extraction of the system mass

The so-called stationary Ha line of SS 433 is shown to consist of three components. A broad component is identified as emitted in that wind from the accretion disk that grows in speed with elevation above the plane of the disk. There are two narrow components, one permanently redshifted and the other permanently shifted to the blue. These are remarkably steady in wavelength and must be emitted from a circumbinary ring, orbiting the center of mass of the system rather than orbiting either the compact object or its companion: perhaps the inner rim of an excretion disk. The orbiting speed ( approximately 200 km s(-1)) of this ring material strongly favors a large mass for the enclosed system ( around 40), a large mass ratio for SS 433, a mass for the compact object, plus accretion disk of similar to 16 M-circle dot, and hence the identity of the compact object as a rather massive stellar black hole.