2010MNRAS.403..760G

We report the discovery of a new Wolf-Rayet star in Aquila via detection of its circumstellar nebula (reminiscent of ring nebulae associated with late WN stars) using the Spitzer Space Telescope archival data. Our spectroscopic follow-up of the central point source associated with the nebula showed that it is a WN7h star (we named it WR121b). We analysed the spectrum of WR121b by using the Potsdam Wolf-Rayet model atmospheres, obtaining a stellar temperature of ≃50kK. The stellar wind composition is dominated by helium with ∼20 per cent of hydrogen. The stellar spectrum is highly reddened [ E(B - V) = 2.85mag]. Adopting an absolute magnitude of M_v= -5.7, the star has a luminosity of logL/L_☉ = 5.75 and a mass-loss rate of 10^–4.7M_☉/yr, and resides at a distance of 6.3kpc. We searched for a possible parent cluster of WR121b and found that this star is located at ≃1° from the young star cluster embedded in the giant Hii region W43 (containing a WN7+a/OB? star - WR121a). We also discovered a bow shock around the O9.5III star ALS9956, located at from the cluster. We discuss the possibility that WR121b and ALS9956 are runaway stars ejected from the cluster in W43.