title: ALMA Compact Array observations of the Fried Egg nebula: Evidence for large-scale asymmetric mass-loss from the yellow hypergiant IRAS 17163-3907.
abstract: 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 the12CO J=2-1 line, H30αrecombination 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 H30αshows unresolved emission at the star, with an approximately gaussian spectrum centered on a velocity of 21±3 km s-1with a width of 57±6 km 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-1and with an expansion velocity of 100±10 km 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 byHerschel. The kinematics of this ring, however, is not consistent with an expanding shell, but show a velocity gradient ofvsys±20 km 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-1relative 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.
authors.affiliation: Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439-92 Onsala, Sweden.
authors.forename: S H J
authors.initials: SH
authors.lastname: Wallström
authors.affiliation: Laboratoire Lagrange, UMR7293, Université Côte d'Azur, CNRS, Observatoire de la Côte d'Azur, Boulevard de l'Observatoire, 06304 Nice Cedex 4, France.
authors.forename: E
authors.initials: E
authors.lastname: Lagadec
authors.affiliation: Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439-92 Onsala, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Muller
authors.affiliation: Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439-92 Onsala, Sweden.
authors.forename: J H
authors.initials: JH
authors.lastname: Black
authors.affiliation: Université de Toulouse, UPS-OMP, IRAP, 31028, Toulouse, France; CNRS, IRAP, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse, France.
authors.forename: N L J
authors.initials: NL
authors.lastname: Cox
authors.affiliation: Instituto de Radioastronomía y Astrofísica, UNAM, A.P. 3-72, Xangari, Morelia, 58089, Mexico.
authors.forename: R
authors.initials: R
authors.lastname: Galván-Madrid
authors.affiliation: Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439-92 Onsala, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Justtanont
authors.affiliation: Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF, UK.
authors.forename: S
authors.initials: S
authors.lastname: Longmore
authors.affiliation: Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439-92 Onsala, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Olofsson
authors.affiliation: School of Physics and Astronomy, The University of Leeds, Leeds, LS2 9JT, UK.
authors.forename: R D
authors.initials: RD
authors.lastname: Oudmaijer
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Inés de la Cruz 3, E-28049 Cantoblanco, Spain.
authors.forename: G
authors.initials: G
authors.lastname: Quintana-Lacaci
authors.affiliation: Nicolaus Copernicus Astronomical Center, Rabianska 8, 87-100 Torun, Poland.
authors.forename: R
authors.initials: R
authors.lastname: Szczerba
authors.affiliation: Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439-92 Onsala, Sweden.
authors.forename: W
authors.initials: W
authors.lastname: Vlemmings
authors.affiliation: Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Heverlee, Belgium.
authors.forename: H
authors.initials: H
authors.lastname: van Winckel
authors.affiliation: Jodrell Bank Centre for Astrophysics, Alan Turing Building, Manchester M13 9PL, UK.
authors.forename: A
authors.initials: A
authors.lastname: Zijlstra
keywords: circumstellar matter; stars: AGB and post-AGB; stars: individual: IRAS 17163–3907; stars: mass-loss