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

TL;DR

This study conducted a near-infrared spectroscopic survey of the Scutum-Crux arm, discovering 17 Wolf-Rayet stars, mostly newly identified, and providing refined classification criteria and insights into their distribution and association with star clusters.

Contribution

It presents the first large-scale near-infrared survey of Wolf-Rayet stars in the Scutum-Crux arm, identifying new stars and developing improved classification diagnostics.

Findings

17 Wolf-Rayet stars discovered, 16 new

Most new WR stars are narrow-lined WN5-7 types

Only a quarter of WR stars are associated with clusters

Abstract

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.