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Detailing evolved star wind complexity: comparing maser and thermal imaging

Published online by Cambridge University Press:  30 November 2022

A.M.S. Richards Open the ORCID record for A.M.S. Richards [Opens in a new window] ,
K.A. Assaf ,
A. Baudry ,
L. Decin ,
S. Etoka Open the ORCID record for S. Etoka [Opens in a new window] ,
M.D. Gray ,
B. Pimpanuwat  and
the ATOMIUM collaboration
A.M.S. Richards
Affiliation:
JBCA, University of Manchester, M15 9PL, UK email: a.m.s.richards@manchester.ac.uk
K.A. Assaf
Affiliation:
JBCA, University of Manchester, M15 9PL, UK email: a.m.s.richards@manchester.ac.uk Dept. of Physics, College of Science, University of Wasit, Iraq
A. Baudry
Affiliation:
Université de Bordeaux, Laboratoire d’Astrophysique de Bordeaux, 33615, Pessac, France
L. Decin
Affiliation:
Instituut voor Sterrenkunde, KU Leuven, Leuven, Belgium
S. Etoka
Affiliation:
JBCA, University of Manchester, M15 9PL, UK email: a.m.s.richards@manchester.ac.uk
M.D. Gray
Affiliation:
JBCA, University of Manchester, M15 9PL, UK email: a.m.s.richards@manchester.ac.uk
B. Pimpanuwat
Affiliation:
JBCA, University of Manchester, M15 9PL, UK email: a.m.s.richards@manchester.ac.uk
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Abstract

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Maser properties can be measured with milli-arcsec precision over multiple epochs using ALMA, cm- and mm-wave VLBI and e-MERLIN. This allows: (i) Tracing SiO maser proper motions in the pulsation-dominated zone; (ii) Quantifying clumpiness, variability and asymmetry of the wind traced by masers; (iii) Contrasting behaviour from OH masers even at similar distances from the star; (iv) Measuring magnetic fields. Mass lost from the star, traced by SiO masers, is likely to take decades to reach ∼5 stellar radii. At 5–50 stellar radii, once dust is well formed, 22-GHz H2O masers show the wind accelerating through the escape velocity; its overall direction is away from the star but the velocity field is complex. In a few cases (so far), highly-directed, localised ejecta are seen. Magnetic fields appear to be stellar-centred and strong enough to influence wind kinematics. Recent ALMA and other observations have shown that otherwise inconspicuous companions shape a majority of evolved star winds, whilst advanced models demonstrate how, for some situations, this is compatible with masers showing negligible rotation proper motions. The long-term monitoring achievable at radio frequencies complements the multi-transition maser studies and analysis of thermal lines and dust at shorter wavelengths.

Keywords

stars: AGBstars: supergiantsmasersstars: mass losswindsoutflows
Type
Contributed Paper
Information
Proceedings of the International Astronomical Union , Volume 16 , Symposium S366: The Origin of Outflows in Evolved Stars , November 2020 , pp. 204 - 209
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Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
© The Author(s), 2022. Published by Cambridge University Press on behalf of International Astronomical Union

Footnotes

†

See Gottlieb et al. 2022 for list.

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