Revealing evolved massive stars with Spitzer

TL;DR

This study used archival Spitzer 24 μm data to discover 115 nebulae around evolved massive stars, mainly LBVs and related stars, enhancing understanding of their evolution and mass-loss processes.

Contribution

It presents the first large-scale identification of circumstellar nebulae around evolved massive stars using Spitzer data, linking nebulae to specific stellar types and supporting their evolutionary significance.

Findings

Discovered 115 nebulae resembling those around LBVs and WNL stars.

Follow-up spectroscopy identified many central stars as candidate LBVs, blue supergiants, or WNL stars.

Detected arc-like structures associated with known LBVs in the LMC.

Abstract

Massive evolved stars loss a large fraction of their mass via copious stellar wind or instant outbursts and during certain evolutionary phases they can be identified via the presence of their circumstellar nebulae. In this paper, we present the results of search for compact nebulae (reminiscent of circumstellar nebulae around evolved massive stars) using archival 24 $\mu$m data obtained with the Multiband Imaging Photometer for Spitzer. We discovered 115 nebulae, most of which bear a striking resemblance to the circumstellar nebulae associated with Luminous Blue Variables (LBVs) and late WN-type (WNL) Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). We interpret this similarity as an indication that the central stars of detected nebulae are either LBVs or related evolved massive stars. Our interpretation is supported by follow-up spectroscopy of two dozens of these central stars, most of which turns out to be either candidate LBVs (cLBVs), blue supergiants or WNL stars. We expect that the forthcoming spectroscopy of the remaining objects from our list, accompanied by the spectrophotometric monitoring of the already discovered cLBVs, will further increase the known population of Galactic LBVs, which in turn would have profound consequences for better understanding the LBV phenomenon and its role in the transition between hydrogen burning O stars and helium burning WR stars. We also report the detection of an arc-like structure attached to the cLBV HD326823 and an arc associated with the LBV R99 (HD269445) in the LMC.