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Atmospheres and wind properties of non-spherical AGB stars
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.ORCID iD: 0000-0001-7662-4184
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
(English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed) Submitted
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-348123OAI: oai:DiVA.org:uu-348123DiVA, id: diva2:1196664
Available from: 2018-04-10 Created: 2018-04-10 Last updated: 2018-04-10
In thesis
1. Stellar Winds of Cool Giants: Investigating the Mass-Loss Mechanism of AGB Stars
Open this publication in new window or tab >>Stellar Winds of Cool Giants: Investigating the Mass-Loss Mechanism of AGB Stars
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Asymptotic giant branch (AGB) stars are luminous cool giants of low to intermediate mass that are strongly pulsating and non-spherical, with heavy mass loss through a stellar wind. The mass loss makes these stars important for galactic chemistry, as the wind enriches the interstellar medium with new elements and dust, and it determines the final fate of these stars.

The winds of AGB stars are believed to be driven by a combination of pulsation-induced shocks and radiation pressure on dust grains, which form in the atmospheres. The two processes, pulsation and mass loss, are usually simulated using different computational codes, as the physical environment of the atmosphere, where the wind is driven, is vastly different from the interior, where the pulsations originate. In this work we try to bridge this gap.

The dynamical atmosphere and wind code DARWIN is used to study dust driven winds. An extensive grid of DARWIN models is constructed to investigate how the mass-loss rates depend on different stellar parameters. The models reproduce observed dynamical properties and we find a strong correlation between mass-loss rates and luminosities.

The simplified description of stellar pulsation in standard DARWIN models, however, introduces free parameters that need to be constrained. The atmosphere models are highly non-linear and even moderate changes to the pulsation properties may have significant impact on the mass-loss rate and wind velocity.

To self-consistently model the pulsation process, and to study atmospheric structures caused by the convection, the radiation hydrodynamical code CO5BOLD is used to produce an exploratory grid of 3D star-in-a-box models. The resulting models have realistic radii and periods, and give important insights into the complex non-spherical structure of AGB stars. Pulsation properties are derived from the CO5BOLD models and used as input in the DARWIN models. Average wind properties from models with CO5BOLD input agree with the standard DARWIN models, however the winds show large density variations with time, which may affect comparisons with observations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 74
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1664
Keywords
late-type stars, AGB stars, stellar winds, stellar atmospheres, dust, stellar pulsation, hydrodynamics, radiative transfer
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-348125 (URN)978-91-513-0319-2 (ISBN)
Public defence
2018-05-30, Häggsalen, Ångströmslaboratoriet, Läggerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2018-05-07 Created: 2018-04-10 Last updated: 2018-10-08

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