The mass of SS 433: a conflict resolved?
Abstract
The Galactic microquasar SS\,433 is very luminous and launches oppositely-directed jets of cool hydrogen at a quarter of the speed of light. Observations of emission lines from the circumbinary disk imply a system mass exceeding 40 M. The most recent attempts to establish a mass via observation of absorption lines in the spectrum of the companion imply a system mass of no more than 20 M. Aims. To examine these conflicting data and present a possible resolution of this conflict. Methods. Interpretation of data through the application of simple trigonometry to the configuration of the SS 433 system. Results. The absorption spectra which, attributed to the atmosphere of the companion, yield an orbital speed of 60 km s-1 could well be attributable to absorption of light from the companion in material of the circumbinary disk. Then the absorption spectra predict an orbital speed for the circumbinary disk material of 240 km s-1, in agreement with the emission line data. Conclusions. If continuum light from the companion is absorbed in passage through the circumbinary disk material rather than in the atmosphere of the companion itself, the periodic Doppler shifts in the absorption spectra are entirely consistent with observations of the circumbinary disk and a system mass exceeding 40 M. The striking consistency implies that the compact object is a rather massive stellar black hole.
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