The VLT/SPHERE view of the A TOMIUM cool evolved star sample: I. Overview: Sample characterization through polarization analysis
Journal article, 2023

Context. Low- and intermediate-mass asymptotic giant stars and massive red supergiant stars are important contributors to the chemical enrichment of the Universe. They are among the most efficient dust factories of the Galaxy, harboring chemically rich circumstellar environments. Yet, the processes that lead to dust formation or the large-scale shaping of the mass loss still escape attempts at modeling. Aims. Through the ATOMIUM project, we aim to present a consistent view of a sample of 17 nearby cool evolved stars. Our goals are to unveil the dust-nucleation sites and morphologies of the circumstellar envelope of such stars and to probe ambient environments with various conditions. This will further enhance our understanding of the roles of stellar convection and pulsations, and that of companions in shaping the dusty circumstellar medium. Methods. Here we present and analyze VLT/SPHERE-ZIMPOL polarimetric maps obtained in the visible (645- 820 nm) of 14 out of the 17 ATOMIUM sources. They were obtained contemporaneously with the ALMA high spatial resolution data. To help interpret the polarized signal, we produced synthetic maps of light scattering by dust, through 3D radiative transfer simulations with the RADMC3D code. Results. The degree of linear polarization (DoLP) observed by ZIMPOL spreads across several optical filters. We infer that it primarily probes dust located just outside of the point spread function of the central source, and in or near the plane of the sky. The polarized signal is mainly produced by structures with a total optical depth close to unity in the line of sight, and it represents only a fraction of the total circumstellar dust. The maximum DoLP ranges from 0.03- 0.38 depending on the source, fractions that can be reproduced by our 3D pilot models for grains composed of olivine, melilite, corundum, enstatite, or forsterite. The spatial structure of the DoLP shows a diverse set of shapes, including clumps, arcs, and full envelopes. Only for three sources do we note a correlation between the ALMA CO ν = 0, J = 2-1 and SiO ν = 0, J = 5-4 lines, which trace the gas density, and the DoLP, which traces the dust. Conclusions. The clumpiness of the DoLP and the lack of a consistent correlation between the gas and the dust location show that, in the inner environment, dust formation occurs at very specific sites. This has potential consequences for the derived mass-loss rates and dust-to-gas ratio in the inner region of the circumstellar environment. Except for π1 Gru and perhaps GY Aql, we do not detect interactions between the circumstellar wind and the hypothesized companions that shape the wind at larger scales. This suggests that the orbits of any other companions are tilted out of the plane of the sky.

Stars: imaging

Stars: evolution

Stars: AGB and post-AGB


Stars: mass-loss

Circumstellar matter


M. Montargès

Paris Observatory

E. Cannon

KU Leuven

A. de Koter

Anton Pannekoek Institute for Astronomy

KU Leuven

Theo Khouri

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

E. Lagadec

Laboratoire Joseph-Louis Lagrange

P. Kervella

Paris Observatory

L. Decin

KU Leuven

University of Leeds

I. McDonald

Open University

University of Manchester

W. Homan

KU Leuven

Université libre de Bruxelles (ULB)

L. B.F.M. Waters

Radboud University

Netherlands Institute for Space Research (SRON)

R. Sahai

Jet Propulsion Laboratory, California Institute of Technology

C. A. Gottlieb

Harvard-Smithsonian Center for Astrophysics

J. Malfait

KU Leuven

S. Maes

KU Leuven

B. Pimpanuwat

National Astronomical Research Institute of Thailand

M. Jeste

Max Planck Society

Taissa Danilovich

KU Leuven

F. De Ceuster

University College London (UCL)

KU Leuven

M. Van De Sande

KU Leuven

University of Leeds

D. Gobrecht

University of Gothenburg

Sofia Wallström

KU Leuven

K. T. Wong

Institut de Radioastronomie Millimétrique (IRAM)

I. El Mellah

Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)

J. Bolte

KU Leuven

F. Herpin

Laboratoire d'Astrophysique de Bordeaux

A. M.S. Richards

University of Manchester

A. Baudry

Laboratoire d'Astrophysique de Bordeaux

S. Etoka

University of Manchester

M. D. Gray

National Astronomical Research Institute of Thailand

University of Manchester

T.J. Millar

Queen's University Belfast

K. M. Menten

Max Planck Society

H. S.P. Müller

University of Cologne

J. M. C. Plane

University of Leeds

J. Yates

University College London (UCL)

A. Zijlstra

University of Manchester

Astronomy and Astrophysics

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

Vol. 671 A96

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Geosciences, Multidisciplinary



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