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
Supergiants
Stars: mass-loss
Circumstellar matter
Author
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 A96Subject Categories
Meteorology and Atmospheric Sciences
Astronomy, Astrophysics and Cosmology
Geosciences, Multidisciplinary
DOI
10.1051/0004-6361/202245398