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Patterns in water maser emission of evolved stars on the timescale of decades

Published online by Cambridge University Press:  07 February 2024

Jan Brand Open the ORCID record for Jan Brand [Opens in a new window] ,
Dieter Engels Open the ORCID record for Dieter Engels [Opens in a new window]  and
Anders Winnberg
Jan Brand*
Affiliation:
INAF-Istituto di Radioastronomia, Bologna, Italy;
Dieter Engels
Affiliation:
Hamburger Sternwarte, Hamburg, Germany;
Anders Winnberg
Affiliation:
Onsala Rymdobservatorium, Onsala, Sweden
*
email: brand@ira.inaf.it
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Abstract

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We present our past and current long-term monitoring program of water masers in the circumstellar envelopes of evolved stars, augmented by occasional interferometric observations. Using as example the Mira-variable U Her, we identify three types of variability: periodic (following the optical variation), long-term (years-decades) and short-term irregular (weeks-months). We show there are regions in the maser shell where excitation conditions are favourable, which remain stable for many years. Lifetimes of maser clouds in the wind-acceleration zone are of the order of up to a few years. Much longer lifetimes are found for the peculiar case of a maser cloud outside that zone (as in RT Vir), or in some cases where the motion of spectral features can be followed for the entire 2 decade monitoring period (as in red supergiant VX Sgr).

Keywords

AGB and post-AGB starswater masersmonitoring
Type
Contributed Paper
Information
Proceedings of the International Astronomical Union , Volume 18 , Symposium S380: Cosmic Masers: Proper Motion toward the Next-Generation Large Projects , December 2022 , pp. 319 - 323
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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 (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2024. Published by Cambridge University Press on behalf of International Astronomical Union

References

Brand, J., Baldacci, L., & Engels, D. 2002, in: V. Migenes & M.J. Reid (eds.), Cosmic Masers: From Proto-Stars to Black Holes, Proc. IAU Symposium No. 206 (San Francisco: ASP), p. 310CrossRefGoogle Scholar
Brand, J., Engels, D. & Winnberg, A. 2018, in: A. Tarchi, M.J. Reid & P. Castangia (eds.), Astrophysical Masers: Unlocking the Mysteries of the Universe, Proc. IAU Symposium No. 336 (CUP), p. 393CrossRefGoogle Scholar
Brand, J., Engels, D., & Winnberg, A. 2020, A&A 644, A45 Google Scholar
Engels, D., Brand, J., & Winnberg, A. 2021, Poster at: The Origin of Outflows in Evolved Stars, IAU Symposium No. 366. Leuven, Belgium. Zenodo. https://doi.org/10.5281/zenodo.5702619 CrossRefGoogle Scholar
Murakawa, K., Yates, J. A., Richards, A.M.S., & Cohen, R. J. 2003, MNRAS 344, 1 CrossRefGoogle Scholar
Winnberg, A., Engels, D., Brand, J., Baldacci, L., & Walmsley, C.M. 2008, A&A 482, 831 Google Scholar
Winnberg, A., Brand, J., & Engels, D. 2011, in: F. Kerschbaum, T. Lebzelter & R.F. Wing (eds.), Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants, ASP-CS 445, p. 375Google Scholar