Revealing evolved massive stars with Spitzer, WISE and SALT

TL;DR

This study uses optical spectroscopy to identify and classify evolved massive stars, including LBVs and rare Wolf-Rayet stars, through infrared nebulae observations, revealing new stellar members and their characteristics.

Contribution

It provides the first spectroscopic confirmation of candidate evolved massive stars identified via infrared nebulae, including new LBVs and rare Wolf-Rayet stars, expanding the known population.

Findings

Discovered about two dozen emission-line stars.

Confirmed four new bona fide LBVs through spectral and brightness changes.

Identified a rare [WN] star and an extragalactic WN3 star in a binary system.

Abstract

We present the results of optical spectroscopic observations of 54 candidate evolved massive stars revealed through the detection of mid-infrared nebulae of various shapes surrounding them with the {\it Spitzer Space Telescope} and {\it Wide-field Infrared Survey Explorer}. These observations, carried out with the Southern African Large Telescope (SALT) in 2010-2015, led to the discovery of about two dozens emission-line stars, of which 15 stars we classify as candidate luminous blue variables (cLBVs). Spectroscopic and photometric monitoring revealed significant changes in the spectra and brightness of four newly identified cLBVs, meaning that they are new members of the class of bona fide LBVs. We present an updated list of the Galactic bona fide LBVs. Currently, this list contains eighteen stars, of which more than 70 per cent are associated with circumstellar nebulae. We also discovered a very rare [WN] star - the central star of the planetary nebula Abell 48, and a WN3 star in a close, eccentric binary system with an O6V star in the Large Magellanic Cloud - the first-ever extragalactic massive star identified via detection of a circular shell around it. Most of the remaining targets are tentatively classified as OB, A and M stars.