A double detached shell around a post-Red Supergiant:IRAS 17163-3907, the Fried Egg nebula

TL;DR

This study presents the first direct mid-infrared images of IRAS 17163, revealing a double detached shell indicative of episodic mass-loss in a post-Red Supergiant star, enhancing understanding of stellar evolution and mass-loss mechanisms.

Contribution

First direct mid-infrared imaging of IRAS 17163, identifying a double detached shell and providing insights into its mass-loss history and evolutionary status.

Findings

IRAS 17163 is a Post-Red Supergiant, possibly a Yellow Hypergiant.

Detected a double dusty detached shell around the star.

Mass-loss occurred in episodes over approximately 400 years.

Abstract

We performed a mid-infrared imaging survey of evolved stars in order to study the dust distribution in circumstellar envelopes around these objects and to better understand the mass-loss mechanism responsible for the formation of these envelopes. During this survey, we resolved for the first time the circumstellar environment of IRAS 17163-3907 (hereinafter IRAS17163), which is one of the brightest objects in the mid-infrared sky, but is surprisingly not well studied. Our aim is to determine the evolutionary status of IRAS 17163 and study its circumstellar environment in order to understand its mass-loss history. We obtained diffraction-limited images of IRAS 17163 in the mid-infrared using VISIR on the VLT. Optical spectra of the object allowed us to determine its spectral type and estimate its distance via the presence of diffuse interstellar bands. We show that IRAS 17163 is a Post-Red Supergiant, possibly belonging to the rare class of Yellow Hypergiants, and is very similar to the well studied object IRC +10420. Our mid-infrared images of IRAS 17163 are the first direct images of this bright mid-infrared source. These images clearly show the presence of a double dusty detached shell around the central star, due to successive ejections of material with a timescale of the order of 400 years and a total circumstellar mass larger than 4 M$_{\odot}$. This indicates that non quiescent mass-loss occurs during this phase of stellar evolution.