  We present archive ESO VLT photometric and spectroscopic data of the
Ultraluminous X-ray source NGC 1313 X-2. The superb quality of the VLT images
reveals that two distinct objects, with R magnitudes 23.7 and 23.6, are visible
inside the Chandra error box. The two objects, separated by 0.75 arcsec, were
unresolved in our previous ESO 3.6 m+EFOSC image. We show that both are stars
in NGC 1313, the first a B0-O9 main sequence star of ~20 Msun, while the second
a G supergiant of ~10 Msun. Irrespectively of which of the two objects the
actual counterpart is, this implies that NGC 1313 X-2 is a high mass X-ray
binary with a very massive donor.

Astrophysics