Discovery of a new Wolf-Rayet star and its ring nebula in Cygnus

We report the serendipitous discovery of a ring nebula around a candidate Wolf–Rayet (WR) star, HBHA 4202-22, in Cygnus using the Spitzer Space Telescope archival data. Our spectroscopic follow-up observations confirmed the WR nature of this star (we named it WR 138a) and showed that it belongs to the WN8-9h subtype. We thereby add a new example to the known sample of late WN stars with circumstellar nebulae. We analysed the spectrum of WR 138a by using the Potsdam Wolf–Rayet (PoWR) model atmospheres, obtaining a stellar temperature of 40 kK. The stellar wind composition is dominated by helium with 20 per cent of hydrogen. The stellar spectrum is highly reddened and absorbed (EB−V = 2.4 mag, AV = 7.4 mag). Adopting a stellar luminosity of log L/L� = 5.3, the star has a mass