uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Effects of Carbon-excess dependent Mass Loss and Molecular Opacities on Models of C-star Evolution
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy, Division of Astronomy and Space Physics.
Dept. of Physics and Astronomy, University of Victoria, Canada.
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy, Division of Astronomy and Space Physics.
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy, Division of Astronomy and Space Physics.
Show others and affiliations
(English)Manuscript (Other academic)
Abstract [en]

We present models of stellar evolution for a 2Msun-star of initial metallicity Z = 0.01 (scaled solar), with focus on the carbon-star phase, the effects of increasing carbon excess on mass loss and molecular opacities. We employ a new, state-of-the-art theoretical mass-loss prescription for dust-driven winds, which takes effects of the carbon excess into account and implement a set of composition-dependent molecular opacities, which incorporates the changes due to the evolution of the carbon excess. This work should be regarded as an exploratory and comparative study. The stellar evolution models were computed using the MESA code-package (http://mesa.sourceforge.net), which includes a new fast and efficient code for stellar evolution, but still needs further calibration before quantitative comparisons with observations can be made. We find that the development of the carbon excess is controlling much of the carbon-star evolution. A very pronounced superwind is forming and the termination of the AGB happens soon after the star becomes carbon rich, in fact, after only 4-5 thermal pulses, which is much less than in existing models.

National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy; Physics
Identifiers
URN: urn:nbn:se:uu:diva-99623OAI: oai:DiVA.org:uu-99623DiVA: diva2:208324
Available from: 2009-03-17 Created: 2009-03-17 Last updated: 2010-01-14
In thesis
1. On the Winds of Carbon Stars and the Origin of Carbon: A Theoretical Study
Open this publication in new window or tab >>On the Winds of Carbon Stars and the Origin of Carbon: A Theoretical Study
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Carbon is the basis for life, as we know it, but its origin is still largely unclear. Carbon-rich Asymptotic Giant Branch (AGB) stars (carbon stars) play an important rôle in the cosmic matter cycle and may contribute most of the carbon in the Galaxy.

In this thesis it is explored how the dust-driven mass loss of these stars depends on the basic stellar parameters by computing a large grid of wind models. The existence of a critical wind regime and mass-loss thresholds for dust-driven winds are confirmed. Furthermore, a steep dependence of mass loss on carbon excess is found. Exploratory work on the effects of different stellar metallicities and the sizes of dust grains shows that strong dust-driven winds develop also at moderately low metallicities, and that typical sizes of dust grains affect the wind properties near a mass-loss threshold.

It is demonstrated that the mass-loss rates obtained with the wind models have dramatic consequences when used in models of carbon-star evolution. A pronounced superwind develops soon after the star becomes carbon rich, and it therefore experiences only a few thermal pulses as a carbon star before the envelope is lost. The number of dredge-up events and the thermal pulses is limited by a self-regulating mechanism: each thermal pulse dredges up carbon, which increases the carbon excess and hence also the mass-loss rate. In turn, this limits the number of thermal pulses.

The mass-loss evolution during a thermal pulse (He-shell flash) is considered as an explanation of the observations of so-called detached shells around carbon stars. By combining models of dust-driven winds with a stellar evolution model, and a simple hydrodynamic model of the circumstellar envelope, it is shown that wind properties change character during a He-shell flash such that a thin detached gas shell can form by wind-wind interaction.

Finally, it is suggested that carbon stars are responsible for much of the carbon in the interstellar medium, but a scenario where high-mass stars are major carbon producers cannot be excluded. In either case, however, the carbon abundances of the outer Galactic disc are relatively low, and most of the carbon has been released quite recently. Thus, there may neither be enough carbon, nor enough time, for more advanced carbon-based life to emerge in the outer Galaxy. This lends some support to the idea that only the mid-part of the Galactic disc can be a “Galactic habitable zone”, since the inner parts of the Galaxy are plagued by frequent supernova events that are presumably harmful to all forms of life.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 105 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 625
Keyword
AGB stars, carbon stars, mass loss, stellar winds, circumstellar matter, cosmic dust, stellar evolution, nucleosynthesis, galactic chemical evolution
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy; Physics
Identifiers
urn:nbn:se:uu:diva-99593 (URN)978-91-554-7472-0 (ISBN)
Public defence
2009-04-29, Ångströmlaboratoriet, Sal 4001, Lägerhyddsvägen 1, Uppsala, 14:00 (English)
Opponent
Supervisors
Available from: 2009-04-08 Created: 2009-03-16 Last updated: 2010-12-08Bibliographically approved

Open Access in DiVA

No full text

Authority records BETA

Mattsson, Lars

Search in DiVA

By author/editor
Mattsson, Lars
By organisation
Department of Physics and AstronomyDivision of Astronomy and Space Physics
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 530 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf