New Wolf-Rayet star and its circumstellar nebula in Aquila

TL;DR

This paper reports the discovery and detailed analysis of a new Wolf-Rayet star, WR121b, in Aquila, including its spectral properties, potential origin, and surrounding nebula, using archival infrared data and spectroscopic modeling.

Contribution

The study presents the first identification of WR121b and its circumstellar nebula, providing detailed spectroscopic characterization and insights into its possible ejection from a nearby star cluster.

Findings

WR121b is a WN7h Wolf-Rayet star with a temperature of ~50 kK.

The star has a luminosity of log L/Lsun = 5.75 and a mass-loss rate of 10^{-4.7} Msun/yr.

WR121b is likely a runaway star ejected from the W43 star cluster.

Abstract

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 analyzed the spectrum of WR121b by using the Potsdam Wolf-Rayet (PoWR) model atmospheres, obtaining a stellar temperature of ~ 50 kK. The stellar wind composition is dominated by helium with ~ 20 per cent of hydrogen. The stellar spectrum is highly reddened (E_{B-V} = 2.85 mag). Adopting an absolute magnitude of M_v = -5.7, the star has a luminosity of log L/Lsun = 5.75 and a mass-loss rate of 10^{-4.7} Msun/yr, and resides in a distance of 6.3 kpc. We searched for a possible parent cluster of WR121b and found that this star is located at ~ 1 degree 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 ~ 0.5 degree from the cluster. We discuss the possibility that WR121b and ALS9956 are runaway stars ejected from the cluster in W43.