A deep near-infrared spectroscopic survey of the Scutum-Crux arm for Wolf-Rayet stars

We present an NTT/SOFI spectroscopic survey of infrared selected Wolf-Rayet candidates in the Scutum-Crux spiral arm (298 < l < 340, |b| < 0.5). We obtained near-IR spectra of 127 candidates, revealing 17 Wolf-Rayet stars - a ~13% success rate - of which 16 are newly identified here. The majority of the new Wolf-Rayet stars are classified as narrow-lined WN5-7 stars, with 2 broad-lined WN4-6 stars and 3 WC6-8 stars. The new stars, with distances estimated from previous absolute magnitude calibrations, have no obvious association with the Scutum-Crux arm. Refined near-infrared (YHJK) classification criteria based on over a hundred Galactic and Magellanic Cloud WR stars, providing diagnostics for hydrogen in WN stars, plus the identification of WO stars and intermediate WN/C stars. Finally, we find that only a quarter of WR stars in the survey region are associated with star clusters and/or HII regions, with similar statistics found for Luminous Blue Variables in the Milky Way. The relative isolation of evolved massive stars is discussed, together with the significance of the co-location of LBVs and WR stars in young star clusters

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

We construct revised near-infrared absolute magnitude calibrations for 126 Galactic Wolf-Rayet (WR) stars at known distances, based in part upon recent large scale spectroscopic surveys. Application to 246 WR stars located in the field, permits us to map their galactic distribution. As anticipated, WR stars generally lie in the thin disk (~40pc half width at half maximum) between galactocentric radii 3.5-10kpc, in accordance with other star formation tracers. We highlight 12 WR stars located at vertical distances of >300pc from the midplane. Analysis of the radial variation in WR subtypes exposes a ubiquitously higher N_{WC}/N_{WN} ratio than predicted by stellar evolutionary models accounting for rotation. Models for non-rotating stars or accounting for close binary evolution are more consistent with observations. We consolidate information acquired about the known WR content of the Milky Way to build a simple model of the complete population. We derive observable quantities over a range of wavelengths, allowing us to estimate a total number of 1200(+300,-100) Galactic WR stars, implying an average duration of ~0.25Myr for the WR phase at the current Milky Way star formation rate. Of relevance to future spectroscopic surveys, we use this model WR population to predict follow-up spectroscopy to K_S ~ 13 mag will be necessary to identify 95% of Galactic WR stars. We anticipate that ESA's Gaia mission will make few additional WR star discoveries via low-resolution spectroscopy, though will significantly refine existing distance determinations. Appendix A provides a complete inventory of 322 Galactic WR stars discovered since the VIIth catalogue (313 including Annex), including a revised nomenclature scheme.Comment: 43 pages, 13 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society. Amended as outlined in a published Erratum (2015MNRAS.449.2436R). Galactic WR star catalogue: http://pacrowther.staff.shef.ac.uk/WRcat