Towards abundance determination from dynamic atmospheres Michael T. Lederer, Thomas Lebzelter, Bernhard Aringer, Walter Nowotny, Josef Hron Department of Astronomy, University of Vienna Stefan Uttenthaler ESO Susanne Höfner Uppsala University

Setting the scene Goal: reliable and accurate element abundances on the AGB Relevant spectral features –atomic lines for metallicity and 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

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

Model & Observation Sc line consists of two components Sc line too strong Molecular lines at wrong positions TiI TiI+VI ScI ScI+at FeI CN OH problems concerning gf-values of atomic lines uncertain positions of molecular lines

Beware of metallicity effects ScI CaI ScI TiI H2OH2O H2OH2O H2OH2O H 2 O+OH H2OH2O CN Water lines decrease with Z Metal lines increase with Z 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)

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

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

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

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

Dynamic Atmospheres Why do we need dynamic model atmospheres? We want to determine abundances along the whole AGB Dynamical effects dominate in the upper part of the AGB Hydrostatic atmospheres cannot describe 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

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

Complex line formation

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

Outlook Matching dynamic models to observed objects Parameter studies in dynamic 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 for stellar evolutionary and mixing models

Conference invitation Registration deadline: Feb 28, 2006 C/O core convective shell atmosphere dust formation region persons with a sweet tooth