TYC 3159-6-1: a runaway blue supergiant

We report the results of optical spectroscopy of a candidate evolved massive star in the CygnusX region, TYC3159-6-1, revealed via detection of its curious circumstellar nebula in archival data of the Spitzer Space Telecope. We classify TYC3159-6-1 as an O9.5 O9.7Ib star and derive its fundamental parameters by using the stellar atmosphere code fastwind. The He and CNO abundances in the photosphere of TYC3159-6-1 are consistent with the solar abundances, suggesting that the star only recently evolved off the main sequence. Proper motion and radial velocity measurements for TYC3159-6-1 show that it is a runaway star. We propose that Dolidze7 is its parent cluster. We discuss the origin of the nebula around TYC3159-6-1 and suggest that it might be produced in several successive episodes of enhanced mass-loss rate (outbursts) caused by rotation of the star near the critical, -limit.