| 1. |
- Lederer, M.T., et al.
(författare)
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Towards abundance determination from dynamic atmospheres
- 2006
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Ingår i: Memorie della Societa Astronomica Italiana, v.77. ; , s. 1008-1013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We summarize our efforts to determine element abundances (e.g. for the elements C and O) and isotopic ratios (e. g. isotope[12]{C}/isotope[13]{C}) along the Asymptotic Giant Branch (AGB). For the modelling of AGB star spectra for stars on the lower part of the AGB, hydrostatic model atmospheres have been shown to reproduce observations quite well. Stars climbing up the AGB get more and more dynamic. For these strongly pulsating stars dynamic model atmospheres have to be used in order to reproduce the observed spectra which are dominated by dynamical effects. Both the developments of hydrostatic and dynamic model atmospheres are considered, referring to the problems encountered in the synthesis of cool star spectra. We emphasize the importance of AGB stars in globular clusters, which provide a method to get a homogenous sample of stars well-defined in mass, metallicity, and luminosity. Finally, we point out the relevance of our investigations for stellar evolutionary models.
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| 2. |
- Nowotny, W., et al.
(författare)
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Atmospheric dynamics in carbon-rich Miras : II. Models meet observations
- 2005
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 437:1, s. 285-296
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Tidskriftsartikel (refereegranskat)abstract
- Originating in different depths of the very extended atmospheres of AGB stars, various molecular spectral lines observable in the near-infrared show diverse behaviours and can be used to probe atmospheric dynamics throughout the outer layers of these pulsating red giants. In Nowotny et al. (2005b, A&A, 437, 273, Paper I) time series of synthetic high-resolution spectra were presented, computed from a dynamic model atmosphere for a typical carbon-rich Mira. In this work, line profile shapes, their variations during the lightcycle and radial velocities derived from wavelength shifts are analyzed and compared with results from observed FTS spectra of the C-rich Mira S Cep and other Miras. It is found that the global velocity structure of the model is in qualitative agreement with observations. Radial velocities of molecular lines sampling different layers behave comparably, although some differences are apparant concerning absolute values. A correction factor of p ≈ 1.36 between measured RVs and actual gas velocities is derived for CO Δ v=3 lines. It is shown that dynamic model atmospheres are capable of reproducing Mira spectra without introducing an additional "static layer" proposed by several authors.
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| 3. |
- Nowotny, W., et al.
(författare)
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Modelling NIR molecular lines for Miras
- 2006
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Ingår i: Memorie della Societa Astronomica Italiana, v.77. ; , s. 180-181
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The atmospheric structure of Mira variables is considerably influenced by pulsation. Molecular absorption lines in the near-infrared (NIR), especially second overtone CO lines, show therefore a characteristic behaviour in time-series of high-resolution spectra. We computed synthetic CO line profiles based on a new dynamic model atmosphere and derived radial velocities (RVs) from the Doppler shifted lines. For the first time, we could quantitatively reproduce observations of the very typical, discontinuous RV curves.
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