ALMA Compact Array observations of the Fried Egg nebula: Evidence for large-scale asymmetric mass-loss from the yellow hypergiant IRAS 17163-3907
Journal article, 2017

Yellow hypergiants are rare and represent a fast evolutionary stage of massive evolved stars. That evolutionary phase is characterised by a very intense mass loss, the understanding of which is still very limited. Here we report ALMA Compact Array observations of a 50??-mosaic toward the Fried Egg nebula, around one of the few Galactic yellow hypergiants IRAS 17163-3907. The emission from the 12CO J = 2-1 line, H30? recombination line, and continuum is imaged at a resolution of ~8??, revealing the morphology of the molecular environment around the star. The continuum emission is unresolved and peaks at the position of the star. The radio recombination line H30? shows unresolved emission at the star, with an approximately Gaussian spectrum centered on a velocity of 21 ± 3km s-1 with a width of 57 ± 6km s-1. In contrast, the CO 2-1 emission is complex and decomposes into several components beyond the contamination from interstellar gas in the line of sight. The CO spectrum toward the star is a broad plateau, centered at the systemic velocity of +18 km s-1 and with an expansion velocity of 100 ± 10km s-1. Assuming isotropic and constant mass-loss, we estimate a mass-loss rate of 8 ± 1.5 × 10-5M? yr-1. At a radius of 25?? from the star, we detect CO emission associated with the dust ring previously imaged by Herschel. The kinematics of this ring, however, is not consistent with an expanding shell, but show a velocity gradient of vsys ± 20km s-1. In addition, we find a puzzling bright feature radially connecting the star to the CO ring, at a velocity of +40 km s-1 relative to the star. This spur feature may trace a unidirectional ejection event from the star. Our ACA observations reveal the complex morphology around IRAS 17163 and illustrate the breakthroughs that ALMA will bring to the field of massive stellar evolution.

Stars: AGB and post-AGB

Stars: individual: IRAS 17163-3907

Stars: mass-loss

Circumstellar matter

Author

Sofia Wallström

Chalmers, Earth and Space Sciences, Onsala Space Observatory

E. Lagadec

Centre national de la recherche scientifique (CNRS)

Sebastien Muller

Chalmers, Earth and Space Sciences, Onsala Space Observatory

John H Black

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

N. L. J. Cox

Centre national de la recherche scientifique (CNRS)

University of Toulouse

R. Galván-Madrid

Universidad Nacional Autonoma de Mexico

Kay Justtanont

Chalmers, Earth and Space Sciences, Onsala Space Observatory

S. Longmore

Liverpool John Moores University

Hans Olofsson

Chalmers, Earth and Space Sciences, Onsala Space Observatory

R. D. Oudmaijer

University of Leeds

G. Quintana-Lacaci

CSIC - Instituto de Ciencia de Materiales de Madrid (ICMM)

R. Szczerba

Polish Academy of Sciences

Wouter Vlemmings

Chalmers, Earth and Space Sciences, Onsala Space Observatory

H. van Winckel

KU Leuven

A. Zijlstra

Jodrell Bank Centre for Astrophysics

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 597 A99, pp. 1-10 A99

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Roots

Basic sciences

Infrastructure

Onsala Space Observatory

DOI

10.1051/0004-6361/201628416

More information

Latest update

10/30/2018