VLT observations of GRS 1915+105

We present near infrared spectroscopy of the superluminal microquasar GRS 1 915+105 obtained with the first unit of the VLT (1) and the ISAAC spectro-i mager. The emission features detected in the VLT data have been identified as He I, Br gamma, He II and Na I. The detection of Na I is reported here f or the first time, while our confirmation of weak He II emission provides s upport to previous marginal detections of this feature. By comparing the ob served spectra with those of massive stars, we find that our results are ve ry consistent with GRS 1915+105 being a high mass X-ray system with an earl y type primary, as previously proposed by Chaty et al. (1996) and Mirabel e t al. (1997). The VLT spectra also provide evidence of P Cygni profiles, th at turn into blue emission wings when the system is in outburst. This obser ved line profile evolution implies that GRS 1915+105 must be surrounded by an expanding envelope, that is partially blown out during the X-ray outburs ts. The presence of such circumstellar gaseous material around GRS 1915+105 is more naturally understood in the context of a massive luminous star tha n if the system was a low-mass X-ray binary.