Characterizing Wolf-Rayet Stars in the Near- And Mid-Infrared

Abstract

We present refined color-color selection criteria for identifying Wolf-Rayet (WR) stars using available mid-infrared (MIR) photometry from WISE in combination with near-infrared (NIR) photometry from the Two Micron All Sky Survey. Using a sample of spectrally classified objects, we find that WR stars are well distinguished from the field stellar population in the (W 1 − W 2) versus (J − K s ) color-color diagram, and further distinguished from other emission line objects such as planetary nebulae, Be, and cataclysmic variable stars using a combination of NIR and MIR color constraints. As proof of concept we applied the color constraints to a photometric sample in the Galactic plane, located WR star candidates, and present five new spectrally confirmed and classified WC (1) and WN (4) stars. Analysis of the 0.8-5.0 μm spectral data for a subset of known, bright WC and WN stars shows that emission lines (primarily He i) extend into the 3.0-5.0 μm spectral region, although their strength is greatly diminished compared to the 0.8-2.5 μm region. The WR population stands out relative to background field stars at NIR and MIR colors due to an excess continuum contribution, likely caused by free-free scattering in dense winds. Mean photometric properties of known WRs are presented and imply that reddened late-type WN and WC sources are easier to detect than earlier-type sources at larger Galactic radii. WISE W 3 and W 4 images of 10 WR stars show evidence of circumstellar shells linked to mass ejections from strong stellar winds.

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

“…( (23) Chené et al (2013), (24) Rahman, Moon, & Matzner (2011), (25) Anderson et al (2011), (26) Marston et al (2013), (27) Kanarek et al (2014), (28) Davies et al (2012), (29) de La Fuente, Najarro, Davies, & Figer (2013), (30) Borissova et al (2012), (31) Mikles et al (2006), (32) Hyodo et al (2008), (33) Faherty et al (2014) (34) Smith et al (2012), (35) Corradi et al (2010), (36) Gvaramadze et al (2009), (37) Burgemeister et al (2013) He ii This paper has been typeset from a T E X/ L A T E X file prepared by the author.…”

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

“…The 17 planetary nebulae (spectra shown in figure 8) display strong emission in the He i 2.06 µm and Br γ/He i 2.17 µm filters, with little to no continuum. PNe are quite easy to identify, particularly using 2MASS and WISE colour criteria, as described in Faherty et al (2014) and a paper in preparation. We also observed nine emission-line sources which are likely to be emitting YSOs (cf.…”

“…WR stars are intrinsically very hot, and therefore blue, and so it should come as no surprise that no WR stars lie below the cut line, with at least a 0.2 magnitude separation from the main bulk of field stars (chosen at random from the 2MASS and WISE catalogues). The physical reason for the positions of WR stars on the colour-colour diagrams in figure 4 is discussed in detail in Faherty et al (2014). Figure 4 also includes a selection of Galactic planetary nebulae (PNe), selected from the Strasbourg-ESO catalogue (Acker et al 1992), which are one of the primary contaminants in the emission-line candidate sample.…”

“…The weather conditions were (2011), described in more detail in Faherty et al (2014). These plots provide another layer of differentiation during the selection process.…”

USco1621 B and USco1556 B: Two wide companions at the deuterium-burning mass limit in Upper Scorpius

“…The identification of substellar objects in binary systems also allows for an inference with regard to the ages, dis-tances, and metallicities from their brighter and easier to characterise primaries, and to determine the otherwise ambiguous luminosities, effective temperatures, and masses of the companions (e.g. Rebolo et al 1998;Faherty et al 2010;Deacon et al 2014;Gauza et al 2015). Young moving groups, stellar clusters and associations with well determined ages, metallicities and distances are also helpful in the determination of the physical parameters of substellar objects.…”