Infrared spectroscopy of the superluminal Galactic source GRS 1915+105 during the 1994 September outburst

We have obtained K-band IR spectra of the superluminal Galactic source GRS 1915+105 on two different dates. The second spectrum, obtained immediately after a bright X-ray outburst in 1994 September, has shown prominent H and He emission lines. The lines are not Doppler shifted, as are those observed in SS 433, suggesting that the ionized regions in the new source are not related to the twin beams of energetic particles that are believed to be responsible for the observed radio lobes. In contrast to Cygnus X-3, where the companion is likely to be a Wolf-Rayet star, we suggest that GRS 1915+105 is likely to be a low-mass X-ray binary. The IR flux probably arises from free-free emission in a wind flowing out of the accretion disk.