A Hidden Population of Massive Stars with Circumstellar Shells Discovered with the Spitzer Space Telescope

TL;DR

This study uncovers a previously unknown population of highly obscured massive stars with circumstellar shells, primarily detected at 24 microns, revealing a new phase in massive stellar evolution.

Contribution

The paper reports the discovery of a large, previously unknown population of circumstellar shells around massive stars, identified through infrared observations with the Spitzer Space Telescope.

Findings

90% of shells are new discoveries

Most central stars are massive and obscured

Identified a population in a narrow evolutionary phase

Abstract

We have discovered a large number of circular and elliptical shells at 24 microns around luminous central sources with the MIPS instrument on-board the Spitzer Space Telescope. Our archival follow-up effort has revealed 90% of these circumstellar shells to be previously unknown. The majority of the shells is only visible at 24 microns, but many of the central stars are detected at multiple wavelengths from the mid- to the near-IR regime. The general lack of optical counterparts, however, indicates that these sources represent a population of highly obscured objects. We obtained optical and near-IR spectroscopic observations of the central stars and find most of these objects to be massive stars. In particular, we identify a large population of sources that we argue represents a narrow evolutionary phase, closely related or identical to the LBV stage of massive stellar evolution.