Red Eyes on Wolf-Rayet Stars: 60 New Discoveries via Infrared Color Selection

Jon C. Mauerhan (1), Schuyler D. Van Dyk (1), Patrick. W. Morris (2)

(1) Infrared Processing and Analysis Center, California Institute of Technology
(2) NASA Herschel Science Center, California Institute of Technology

We have spectroscopically identified 60 Galactic Wolf-Rayet stars (WRs), including 38 nitrogen types (WN) and 22 carbon types (WC). Using photometry from the textit{Spitzer}/GLIMPSE and Two-Micron All-Sky Survey (2MASS) databases, the new WRs were selected via a method we have established that exploits their unique infrared colors, which is mainly the result of excess radiation generated by free-free scattering within their dense ionized winds. The selection criterion has been refined since the last report, resulting in a WR detection rate of ~20% in spectroscopic follow-up of candidates that comprise a broad color space defined by the color distribution of all known WRs having B>14 mag. However, there are smaller regions within this color space which yield WRs at a rate of >50% in spectroscopic follow-up. Candidates which are not WRs are mainly Be stars, which is possibly attributable to the physical similarities between the free-free emission parameters of Be disks and WR winds. As an additional selection experiment, the list of WR candidates was cross-correlated with archival X-ray point-source catalogs, which increases the WR detection rate of the broad color space to ~40%; ten new WR X-ray sources have been found, in addition to a previously unrecognized X-ray counterpart to a known WR. The extinction values, distances, and galactocentric radii of all new WRs are calculated using the method of spectroscopic parallax. Although the majority of the new WRs have no obvious association with stellar clusters, two WC8 stars reside in a previously unknown massive-star cluster, in which five OB supergiants were also identified. The new system lies at an estimated distance of ~6.1 kpc, near the intersection of the Scutum-Centaurus Arm with the Galaxy's bar. In addition, two WC and four WN stars, all but one of which are X-ray sources, were identified in association with the stellar clusters Danks 1 and 2. A WN9 star has also been associated with the cluster [DBS2003] 179. This work brings the total number of known Galactic WRs to 476, or ~7-8% of the total empirically estimated population. An examination of their Galactic distribution reveals an approximate tracing of the major spiral arms and an enhanced WR surface density toward major, massive-star formation sites.

Reference: arXiv:1105.5134
Status: Manuscript has been accepted


Comments: Article was accepted to the Astronomical Journal on May 20, 2011.