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A Study of Grain Drift in C Stars: Theoretical Modeling of Dust-Driven Winds in Carbon-Rich Pulsating Giant Stars
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A major fraction of stars will pass through a short period of dramatic events in their final evolutionary stage. Low- to intermediate-mass stars, studied here, are stripped of their outer parts in a slow massive wind. This mass loss reshapes both the star and the surrounding medium. The formation of the wind is a consequence of the non-linear interaction of a number of physical processes. Stellar pulsations and efficient dust formation are examples of such key processes. Time-dependent theoretical models, in combination with observations, are useful tools for understanding these winds.

The main object of this thesis has been the physical improvement of a theoretical wind model. Here the coupling between the dust and gas in the wind is studied in further detail, allowing drift. The methods that have been developed earlier to describe the micro-physical interaction are overviewed and summarized. Previously dust has often been assumed to move at the same velocity as gas. New time-dependent wind models are presented where grain drift has been treated self-consistently. Specifically, the coupling between dust and gas in the wind has been modeled more realistically, with descriptions of both the modified momentum and energy balances, and drift dependent dust formation. The results of these new ``drift models'' have been compared with the results of non-drift models.

A general result of the study is that the effects of drift are significant and difficult to predict if a simple analytical theory is used. It has been found that dust in drift models tends to accumulate in certain dense regions, an accumulation that was not possible without drift. Moreover the new models show an increased variability in the wind structure. The use of drift in dust formation tends to markedly increase the produced dust. Some sets of model parameters lead to a wind without including drift, but a corresponding wind does not form when drift is included -- and vice versa. The effects of drift are important and can probably not be ignored in realistic models.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2003. , p. 50
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 831
Keyword [en]
Astronomy, hydrodynamics, radiative transfer, instabilities, dust formation, stars: AGB and post-AGB, stars: mass-loss, stars: variables: general
Keyword [sv]
Astronomi
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Theoretical Astrophysics
Identifiers
URN: urn:nbn:se:uu:diva-3397ISBN: 91-554-5609-X (print)OAI: oai:DiVA.org:uu-3397DiVA, id: diva2:162651
Public defence
2003-05-21, Häggsalen, Ångströmlaboratoriet, Uppsala, 10:15
Opponent
Supervisors
Available from: 2003-04-25 Created: 2003-04-25Bibliographically approved
List of papers
1. Three-component modeling of C-rich AGB star winds: I. Method and first results
Open this publication in new window or tab >>Three-component modeling of C-rich AGB star winds: I. Method and first results
2003 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 398, no 1, p. 253-266Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90332 (URN)
Available from: 2003-04-25 Created: 2003-04-25Bibliographically approved
2. Three-component modeling of C-rich AGB star winds: II. The effects of drift in long-period variables
Open this publication in new window or tab >>Three-component modeling of C-rich AGB star winds: II. The effects of drift in long-period variables
2003 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 404, p. 789-807Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90333 (URN)
Available from: 2003-04-25 Created: 2003-04-25Bibliographically approved
3. Three-component modeling of C-rich AGB star winds: III. Micro-physics of drift-dependent dust formation
Open this publication in new window or tab >>Three-component modeling of C-rich AGB star winds: III. Micro-physics of drift-dependent dust formation
2004 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 413, p. 789-98Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90334 (URN)
Available from: 2003-04-25 Created: 2003-04-25Bibliographically approved

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