Identification of the donor in the X-ray binary GRS 1915+105

We report on the results of medium-resolution spectroscopy of GRS 1915+105 in the near-infrared H and K band using the 8 m VLT at ESO. We clearly identify absorption bandheads from 12 CO and 13 CO. Together with other features this results in a classication of the mass-donating star in this binary as a K-M III star, clearly indicating that GRS 1915+105 belongs to the class of low-mass X-ray binaries (LMXB).