Discovery of a new Wolf Rayet star and its ring nebula in Cygnus
V.V. Gvaramadze1, S. Fabrica2, W.-R. Hamann3, O. Sholukhova2, A.F. Valeev2, V.P. Goranskij1, A.M. Cherepashchuk1, D.J. Bomans4, L.M. Oskinova3
2Special Astrophysical Observatory, Nizhnij Arkhyz 369167, Russia
3Institut für Physik und Astronomie, Universität Potsdam, Germany
4Astronomical Institute, Ruhr-University Bochum, Universitätstr. 150, 44780 Bochum, Germany
We report the serendipitous discovery of a ring nebula around a candidate Wolf Rayet (WR) star, HBHA4202-22, in Cygnus using the Spitzer Space Telescope archival data. Our spectro-scopic follow-up observations confirmed the WR nature of this star (we named it WR138a) 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 WR138a 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-loss rate of 10-4.7 Msun/yr, and resides in a distance of 4.2 kpc. We measured the proper motion for WR138a and found that it is a runaway star with a peculiar velocity of 50 km/s. Implications of the runaway nature of WR 138a for constraining the mass of its progenitor star and understanding the origin of its ring nebula are discussed.
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