Towards abundance determination from dynamic atmospheres

1. Towards abundance determination from dynamic atmospheres Michael T. Lederer, Thomas Lebzelter, Bernhard Aringer,Walter Nowotny, Josef Hron Department of Astronomy, University of Vienna Stefan UttenthalerESO Susanne HöfnerUppsala University

2. Setting the scene • Goal: reliable and accurate element abundances on the AGB • Relevant spectral features • atomic lines for metallicityand s-process elements • CO lines (isotopes) • OH/CO lines for C/O ratio • A diffcult task! Even more difficult in the case of stars with dynamic atmospheres

3. Lines, lines, everywhere lines! • many strong atomic and molecular lines • strong blending • calibration very difficult • overlapping weak molecular lines form a quasi-continuum which affects the appearance of all stronger lines

4. Molecular lines at wrong positions OH CN FeI ScI+at ScI TiI TiI+VI Sc line consists of two components Sc line too strong Model & Observation • problems concerninggf-values of atomic lines • uncertain positions ofmolecular lines

5. CN H2O+OH H2O H2O H2O+OH Water lines decrease with Z CaI ScI H2O H2O CaI TiI ScI Metal lines increase with Z Beware of metallicity effects • Molecular lines show a complex behaviour as a function of abundances • Changes of the structure and quasi-continuum affect metal lines (may become weaker with higher Z)

6. Consistency • Calculation of model atmospheres and subsequent spectral synthesis require consistent treatment of • Metallicity • Sphericity • Opacity • Inconsistencies lead to wrong spectra making a reliable abundance determination problematic

7. Example: 47 Tuc AGB variable Teff ~ 3600 K, M ~ 0.8 M, L ~ 1300 L, [Fe/H] = -0.66 Gemini South, Phoenix

8. Static models fail here! • „here“ means: for large-amplitude variables • Dynamic effects dominate the spectrum Teff ~ 3600 K, M ~ 0.8 M, L ~ 4500 L, [Fe/H] = -0.66 Gemini South, Phoenix

9. The need for dynamic model atmospheres: observational evidence calculated EW(hydrostatic models) ESO NTT, IRSPEC calculated EW (range) (dynamic models) observed EW Aringer et al. (1999)

10. Dynamic Atmospheres Why do we needdynamic model atmospheres? • We want to determine abundances along the whole AGB • Dynamical effects dominate in the upper part of the AGB • Hydrostatic atmospheres cannotdescribe the spectra of stars with large amplitude pulsations (Miras) • Dynamic model atmospheres(„Höfner-type“, Höfner et al. 2003) • Time dependent description of radiation hydrodynamics and dust formation (C-dust, O-dust in progress) • Pulsation introduced as inner boundary • Mass loss, shock waves

11. Complex density, temperature,and velocity structure significantly shallower density structure Nowotny et al. (2005)

12. Complex line formation

13. Effect on equivalent widths Lebzelter, Aringer, Nowotny (2003)

14. Outlook • Matching dynamic modelsto observed objects • Parameter studies indynamic atmospheres • Abundance determination in Globular Cluster systems in the Magellanic Clouds and the Galaxy (taking into account the influence of dynamics) • Abundances as a test forstellar evolutionary and mixing models

15. C/O core convective shell atmosphere dust formation region Conference invitation www.univie.ac.at/galagb/ Registration deadline: Feb 28, 2006 persons witha sweet tooth