Abstract

A succession of near-infrared (near-IR) spectroscopic observations, taken nightly throughout an entire cycle of SS 433's orbit, reveal (i) the persistent signature of SS 433's accretion disc, having a rotation speed of similar to 500 km s(-1), (ii) the presence of circumbinary disc recently discovered at optical wavelengths by Blundell, Bowler Schmidtobreick (2008) and (iii) a much faster outflow than has previously been measured for the disc wind, with a terminal velocity of similar to 1500 km s(-1). The increased wind terminal velocity results in a mass-loss rate of similar to 10(-4) M(circle dot) yr(-1). These, together with the newly (upwardly) determined masses for the components of the SS 433 system, result in an accurate diagnosis of the extent to which SS 433 has super-Eddington flows. Our observations imply that the size of the companion star is comparable with the semiminor axis of the orbit which is given by, where e is the eccentricity. Our relatively spectral resolution at these near-IR wavelengths has enabled us to deconstruct the different components that comprise the Brackett-gamma (Br gamma) line in this binary system, and their physical origins. With this line being dominated throughout our series of observations by the disc wind, and the accretion disc itself being only a minority (similar to 15 per cent) contribution, we caution against use of the unresolved Br gamma line intensity as an 'accretion signature' in X-ray binaries or microquasars in any quantitative way.