Characterizing Wolf-Rayet stars in the near- and mid-infrared.
FAHERTY J.K., SHARA M.M., ZUREK D., KANAREK G. and MOFFAT A.F.J.
Abstract (from CDS):
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 (W1 - W2) versus (J - Ks) 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 W3 and W4 images of 10 WR stars show evidence of circumstellar shells linked to mass ejections from strong stellar winds.
Galaxy: disk - Galaxy: stellar content - planetary nebulae: general - stars: emission-line, Be - stars: Wolf-Rayet - surveys