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The adventure of carbon stars: Observations and modeling of a set of C-rich AGB stars
Univ Vienna, Dept Astrophys, Turkenschanzstr 17, A-1180 Vienna, Austria..
Univ Vienna, Dept Astrophys, Turkenschanzstr 17, A-1180 Vienna, Austria..
Univ Libre Bruxelles, Inst Astron & Astrophys, Blvd Triomphe CP 226, B-1050 Brussels, Belgium..
Astron Observ Padova INAF, Vicolo Osservatorio 5, I-35122 Padua, Italy..
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 600, A92Article in journal (Refereed) Published
Abstract [en]

Context. Modeling stellar atmospheres is a complex and intriguing task in modern astronomy. A systematic comparison of models with multi-technique observations is the only efficient way to constrain the models. Aims. We intend to perform self-consistent modeling of the atmospheres of six carbon-rich AGB stars (R Lep, R Vol, Y Pav, AQ Sgr, U Hya, and X TrA) with the aim of enlarging the knowledge of the dynamic processes occurring in their atmospheres. Methods. We used VLTI/MIDI interferometric observations, in combination with spectro-photometric data, and compared them with self-consistent, dynamic model atmospheres. Results. We found that the models can reproduce spectral energy distribution (SED) data well at wavelengths longer than 1 mu m, and the interferometric observations between 8 mu m and 10 mu m. Discrepancies observed at wavelengths shorter than 1 mu m in the SED, and longer than 10 mu m in the visibilities, could be due to a combination of data- and model-related effects. The models best fitting the Miras are significantly extended, and have a prominent shell-like structure. On the contrary, the models best fitting the non-Miras are more compact, showing lower average mass loss. The mass loss is of episodic or multi-periodic nature but causes the visual amplitudes to be notably larger than the observed ones. A number of stellar parameters were derived from the model fitting: T-Ross, L-Ross, M, C/O, and. M. Our findings agree well with literature values within the uncertainties. TRoss, and LRoss are also in good agreement with the temperature derived from the angular diameter T(theta((V-K))) and the bolometric luminosity from the SED fitting L-bol, except for AQ Sgr. The possible reasons are discussed in the text. Finally, theta(Ross) and theta((V-K)) agree with one another better for the Miras than for the non-Miras targets, which is probably connected to the episodic nature of the latter models. We also located the stars in the H-R diagram, comparing them with evolutionary tracks. We found that the main derived properties (L, T-eff, C/O ratios and stellar masses) from the model fitting are in good agreement with TP-AGB evolutionary calculations for carbon stars carried out with the COLIBRI code.

Place, publisher, year, edition, pages
EDP SCIENCES S A , 2017. Vol. 600, A92
Keyword [en]
stars: AGB and post-AGB, stars: atmospheres, stars: mass-loss, stars: carbon, techniques: interferometric, techniques: high angular resolution
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-324342DOI: 10.1051/0004-6361/201629337ISI: 000400754000048OAI: oai:DiVA.org:uu-324342DiVA: diva2:1109768
Funder
EU, European Research Council, 615604
Available from: 2017-06-14 Created: 2017-06-14 Last updated: 2017-06-14Bibliographically approved

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