Letter to the Editor

A double detached shell around a post-red supergiant: IRAS 17163-3907, the Fried Egg nebula^⋆,⋆⋆

¹ European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching, Germany
e-mail: elagadec@eso.org
² Jodrell Bank Center For Astrophysics, The University of Manchester, School of Physics & Astronomy, Manchester M13 9PL, UK
³ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
⁴ Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan, 200D, 3001 Leuven, Belgium
⁵ N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Torùn, Poland
⁶ Lab. H. Fizeau, CNRS UMR 6525, Univ. de Nice-Sophia Antipolis, Observatoire de la Côte d’Azur, 06108 Nice, France

Received: 20 June 2011
Accepted: 27 September 2011

Abstract

Context. We performed a mid-infrared imaging survey of evolved stars to study the dust distribution in circumstellar envelopes around these objects and to understand the mass-loss mechanism responsible for the formation of these envelopes better. During this survey, we resolved the circumstellar environment of IRAS 17163-3907 for the first time (hereafter IRAS 17163), which is one of the brightest objects in the mid-infrared sky, but is surprisingly not well studied.

Aims. Our aim is to determine the evolutionary status of IRAS 17163 and study its circumstellar environment to understand its mass-loss history.

Methods. 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 through diffuse interstellar bands.

Results. 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 a double dusty detached shell around the central star, caused by successive ejections of material on a timescale of the order of 400 years and a total circumstellar mass exceeding than 4 M_⊙. This indicates that non-quiescent mass-loss occurs during this phase of stellar evolution.