Searching for hidden Wolf-Rayet stars in the Galactic plane - 15 new Wolf-Rayet stars

Abstract

We report the discovery of 15 previously unknown Wolf-Rayet (WR) stars found as part of an infrared (IR) broad-band study of candidate WR stars in the Galaxy. We have derived an empirically based selection algorithm which has selected ∼5000 WR candidate stars located within the Galactic plane drawn from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (mid-IR) and Two-Micron All-Sky Survey (near-IR) catalogues. Spectroscopic follow-up of 184 of these reveals 11 nitrogen-rich (WN) and four carbon-rich (WC) WR stars. Early WC subtypes are absent from our sample and none shows evidence for circumstellar dust emission. Of the candidates which are not WR stars, ∼120 displayed hydrogen emissionline features in their spectra. Spectral features suggest that the majority of these are in fact B supergiants/hypergiants, ∼40 of these are identified Be/B[e] candidates.Here, we present the optical spectra for six of the newly detected WR stars, and the near-IR spectra for the remaining nine of our sample. With a WR yield rate of ∼7 per cent and a massive star detection rate of ∼65 per cent, initial results suggest that this method is one of the most successful means for locating evolved, massive stars in the Galaxy.

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

“…Shara et al (1991Shara et al ( , 1999 applied similar methods to push the extent of the known Galactic population beyond 5 kpc from the Sun, and extension to near-IR wavelengths has facilitated yet deeper investigation of the Galactic disk (Shara et al 2009(Shara et al , 2012. Another distinctive feature of WR stars -the near-IR excess caused by free-free emission in their winds -has been exploited to yield further discoveries (Homeier et al 2003;Hadfield et al 2007;Mauerhan, Van Dyk & Morris 2011). These efforts, alongside several serendipitous discoveries (e.g., Clark et al 2005, Mauerhan et al 2010a, have brought the recognised Galactic WR star population to ∼635 as of March 2014 1 .…”

Near- and mid-infrared colors of evolved stars in the Galactic plane. TheQ1 andQ2 parameters

“…2, we show a K s −[8.0] versus J−K s diagram. The reddening vector is determined using the near-infrared extinction law by Messineo et al (2005), and the color excess by Indebetouw et al (2005) (Hadfield et al 2007). This WR sequence suffers contamination from late-type stars.…”

“…The Q1-Q2 based criteria provide a detection efficiency comparable to that by Mauerhan et al on the whole sample of WRs. These authors applied additional criteria than the color-color criteria by Hadfield et al (2007), based on the K s versus J−K s diagram. We also reclassified separately their sample of 61 WRs, which is composed of more distant and obscured WR stars with our classification scheme, and retrieved 75% of them as early-type stars, and 73% as free-free emitters (free-1).…”

“…WRs have an infrared excess, due to free-free emission from dense stellar winds (Cohen et al 1975). Hadfield et al (2007) established a successful selection of WRs based on a combination of 2MASS and GLIMPSE colors, which has been recently revised by Mauerhan et al (2011). WRs can be identified by combining three color-color diagrams, the J − H versus J−K s diagram, the [3.6] An overview of near and mid-infrared colors of bright masslosing stars in the Milky Way is missing, and providing one is the purpose of the present work.…”

A near-infrared survey of the inner Galactic plane for Wolf–Rayet stars – III. New methods: faintest WR stars

“…Two earlier papers in this series have focused on photometric techniques, and identified 112 new WR stars in the Galactic Plane (Shara et al 2009, 2012, hereafter Paper I andPaper II, respectively). In addition, various colour-selection criteria in the near-and mid-infrared have been developed; see Hadfield et al (2007), Mauerhan, Van Dyk, & Morris (2009), , and Messineo et al (2012) (as well as Faherty et al (2014) for a discussion of the specific techniques used in this paper).…”