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Wahlin, Rurik
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Publications (7 of 7) Show all publications
Mattsson, L., Wahlin, R. & Höfner, S. (2012). Dust driven mass loss from carbon stars as a function of stellar parameters. I. A grid of solar-metallicity wind models (Corrigendum). Astronomy and Astrophysics, 546, C1.
Open this publication in new window or tab >>Dust driven mass loss from carbon stars as a function of stellar parameters. I. A grid of solar-metallicity wind models (Corrigendum)
2012 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 546, C1- p.Article in journal (Refereed) Published
Abstract [en]

<BR /> Aims: The purpose of this corrigendum is to point out that a handful of models in the original paper were computed with faulty initial structures. <BR /> Methods: Using exactly the same modelling methods we have recomputed the faulty models with new initial structures. <BR /> Results: The new results slightly changes some of the trends in the wind properties with stellar parameters, but the overall effects are small. The conclusions are not affected

Place, publisher, year, edition, pages
edp, 2012
Keyword
stars: AGB and post-AGB, stars: atmospheres, stars: carbon, circumstellar matter, stars: evolution, errata, addenda
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-196837 (URN)10.1051/0004-6361/200912084e (DOI)
Available from: 2013-03-13 Created: 2013-03-13 Last updated: 2017-12-06Bibliographically approved
Abia, C., de laverny, P. & Wahlin, R. (2008). Chemical analysis of carbon stars in the Local Group. Astronomy and Astrophysics, 481(1), 161-168.
Open this publication in new window or tab >>Chemical analysis of carbon stars in the Local Group
2008 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 481, no 1, 161-168 p.Article in journal (Refereed) Published
Abstract [en]

Aims. We present new results of our ongoing chemical study of carbon stars in Local Group galaxies to test the critical dependence of s-process nucleosynthesis on the stellar metallicity. Methods. We collected optical spectra with the VLT/UVES instrument of two carbon stars found in the Carina Dwarf Spheroidal (dSph) galaxy, namely ALW-C6 and ALW-C7. We performed a full chemical analysis using the new generation of hydrostatic, spherically symmetric carbon-rich model atmospheres and the spectral synthesis method in LTE. Results. The luminosities, atmosphere parameters and chemical composition of ALW-C6 and ALW-C7 are compatible with these stars being in the TP-AGB phase undergoing third dredge-up episodes, although their extrinsic nature ( external pollution in a binary stellar system) cannot be definitively excluded. Our chemical analysis shows that the metallicity of both stars agree with the average metallicity ([Fe/H] similar to -1.8 dex) previously derived for this satellite galaxy from the analysis of both low resolution spectra of RGB stars and the observed colour magnitude diagrams. ALW-C6 and ALW-C7 present strong s-element enhancements, [s/Fe] = + 1.6, + 1.5, respectively. These enhancements and the derived s-process indexes [ls/Fe], [hs/Fe] and [hs/ls] are compatible with theoretical s-process nucleosynthesis predictions in low mass AGB stars (similar to 1.5 M(circle dot)) on the basis that the (13)C(alpha, n) (16)O is the main source of neutrons. Furthermore, the analysis of C(2) and CN bands reveals a large carbon enhancement (C/O similar to 7 and 5, respectively), much larger than the values typically found in galactic AGB carbon stars ( C/O similar to 1-2). This is also in agreement with the theoretical prediction that AGB carbon stars are formed more easily through third dredge-up episodes as the initial stellar metallicity drops. However, theoretical low-mass AGB models apparently fail to simultaneously fit the observed s-element and carbon enhancements. On the other hand, Zr is found to be less enhanced in ALW-C7 compared to the other elements belonging to the same s-peak. Although the abundance errors are large, the fact that in this star the abundance of Ti ( which has a similar condensation temperature to Zr) seems also to be lower than those of others metals, may indicate the existence of some depletion into dust-grains in its photosphere.

Keyword
stars : abundances, stars : carbon, galaxies : dwarf, stars : AGB and post AGB, galaxies : Local Group
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-260397 (URN)10.1051/0004-6361:20079114 (DOI)000254195200032 ()
Available from: 2015-08-18 Created: 2015-08-18 Last updated: 2017-12-04Bibliographically approved
Mattsson, L., Höfner, S., Wahlin, R. & Herwig, F. (2007). On the Connection between Mass Loss and Evolution of C-rich AGB Stars. In: Why Galaxies Care About AGB Stars: Their Importance as Actors and Probes (pp. 239-243). .
Open this publication in new window or tab >>On the Connection between Mass Loss and Evolution of C-rich AGB Stars
2007 (English)In: Why Galaxies Care About AGB Stars: Their Importance as Actors and Probes, 2007, 239-243 p.Conference paper, Published paper (Other scientific)
Abstract [en]

The mass-loss properties of carbon rich AGB stars are not very well constrained at present. A variety of empirical or theoretical formulae with different parameterisations are available in the literature and the agreement between them is anything but good. These simple mass-loss prescriptions are nonetheless used in many models of stellar evolution without much consideration of their applicability in various cases. We present here an on-going project aiming at a better description of the mass loss, that could be used to improve stellar evolution models -- especially the evolution during the TP-AGB phase. As a first step, we have considered the mass-loss evolution during a He-shell flash. Using stellar parameters sampled from a stellar evolutionary track, we have computed the time evolution of the atmospheric layers and wind acceleration region during a flash event with detailed frequency-dependent radiation-hydrodynamical models including dust formation. We find that existing simple mass-loss prescriptions imply mass-loss evolutions different than our model. Based on these results, we have also simulated the subsequent long-term dynamical evolution of the circumstellar envelope (CSE), including the formation of a detached shell. The second step of the project deals with the dependence of mass loss on the basic stellar parameters. At the moment we are computing a large grid of wind models for C-rich AGB stars. Preliminary results show that simple parameterisations are difficult to obtain in certain regions of the parameter space considered, due to strong non-linearities in the wind mechanism.

Identifiers
urn:nbn:se:uu:diva-14048 (URN)978-1-58381-318-8 (ISBN)
Available from: 2008-01-29 Created: 2008-01-29
Mattsson, L., Wahlin, R. & Höfner, S. (2007). Thresholds for the Dust Driven Mass Loss from C-rich AGB Stars. In: Stellar Populations as Building Blocks of Galaxies: Proceedings of IAU Symposium #241 (pp. 37-38). .
Open this publication in new window or tab >>Thresholds for the Dust Driven Mass Loss from C-rich AGB Stars
2007 (English)In: Stellar Populations as Building Blocks of Galaxies: Proceedings of IAU Symposium #241, 2007, 37-38 p.Conference paper, Published paper (Other scientific)
Abstract [en]

It is well established that mass loss from AGB stars due to dust driven winds cannot be arbitrarily low. We model the mass loss from carbon rich AGB stars using detailed frequency-dependent radiation hydrodynamics including dust formation. We present a study of the thresholds for the mass loss rate as a function of stellar parameters based on a subset of a larger grid of such models and compare these results to previous observational and theoretical work. Furthermore, we demonstrate the impact of the pulsation mechanism and dust formation for the creation of a stellar wind and how it affects these thresholds and briefly discuss the consequences for stellar evolution.

Identifiers
urn:nbn:se:uu:diva-14042 (URN)doi:10.1017/S1743921307007375 (DOI)
Available from: 2008-01-29 Created: 2008-01-29
Wahlin, R., Mattsson, L., Höfner, S. & Aringer, B. (2007). Towards a low metallicity carbon star spectral library. In: Stellar Populations as Building Blocks of Galaxies: Proceedings of IAU Symposium #241 (pp. 105-106). .
Open this publication in new window or tab >>Towards a low metallicity carbon star spectral library
2007 (English)In: Stellar Populations as Building Blocks of Galaxies: Proceedings of IAU Symposium #241, 2007, 105-106 p.Conference paper, Published paper (Other scientific)
Identifiers
urn:nbn:se:uu:diva-14044 (URN)doi:10.1017/S1743921307007570 (DOI)
Available from: 2008-01-29 Created: 2008-01-29
Wahlin, R., Eriksson, K., Gustafsson, B., Hinkle, K. H., Lambert, D. L., Ryde, N. & Westerlund, B. (2005). Phoenix Spectra of Carbon Stars in the LMC. In: High Resolution Infrared Spectroscopy in Astronomy. .
Open this publication in new window or tab >>Phoenix Spectra of Carbon Stars in the LMC
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2005 (English)In: High Resolution Infrared Spectroscopy in Astronomy, 2005Conference paper, Published paper (Other scientific)
Identifiers
urn:nbn:se:uu:diva-25643 (URN)
Available from: 2007-02-13 Created: 2007-02-13
Ryde, N., Gustafsson, B., Eriksson, K. & Wahlin, R. (2005). The Abundance of Elements in Cool Stars, as Determined from High-Resolution, 1-5 Micron Spectroscopy. High Resolution Infrared Spectroscopy in Astronomy: eds. H. U. Käufl, R. Siebenmorgen, & A. Moorwood, 365-.
Open this publication in new window or tab >>The Abundance of Elements in Cool Stars, as Determined from High-Resolution, 1-5 Micron Spectroscopy
2005 (English)In: High Resolution Infrared Spectroscopy in Astronomy: eds. H. U. Käufl, R. Siebenmorgen, & A. Moorwood, 365- p.Article, review/survey (Other (popular scientific, debate etc.)) Published
Identifiers
urn:nbn:se:uu:diva-77379 (URN)
Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2011-01-11
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