Program: GN-2010B-Q-105

Despite their importance in a number of astrophysical fields, the lifecycles of very massive stars (>60Msun) are still poorly defined. A prominent example of this situation is the most famous member of the Cyg OB2 association, VI Cyg 12, long recognized as one of the intrinsically optically brightest, and potentially most luminous stars in the Galaxy and lying well in excess of the Humphreys-Davidson limit. Its stellar properties are not well constrained, with spectral classifications ranging from mid B to late B hypergiant. The star has not shown significant spectral/photometric variations over the last ten years. Recent quantitative spectroscopic investigations show moderate CNO processing but no traces of helium enrichment, a situation clearly at odds with the one predicted by evolutionary models, suggesting a new evolutionary scenario. We propose to observe the object at highest spatial resolution and moderate spectral resolution in the J, H and K bands with NIFS, at three epochs. This should provide crucial constraints, both spatial and spectroscopic, on the possible multiplicity of the object as well as reveal traces of a possible merger event which may have led Cyg No. 12 to its current location in the H-R diagram.