The challenges of abundance analysis for LPVs Thomas Lebzelter / Walter Nowotny / Bernhard Aringer / Kenneth Hinkle / Susanne Höfner / Ulrike Heiter / and many more... Acknowledging support by the Austrian Science Fund FWF and the ESF
The challenges of
abundance analysis for LPVsThomas Lebzelter / Walter Nowotny / Bernhard Aringer /
Kenneth Hinkle / Susanne Höfner / Ulrike Heiter /
and many more...
Acknowledging support by the Austrian Science Fund FWF
and the ESF
Why abundances from AGB stars?
Surface abundances are changed by third dredge up:
C/O
Isotopic ratios
s-process elements
Important for:
Stellar and Galactic Evolution
Stellar Nucleosynthesis
LPVs are...
Low temperature objects
With an extended atmosphere
And large amplitude variability
A little experiment from 2010
Analysis results for a Tau
Based on R=80 000, S/N=200 spectrum between 4900 and 9750 A
plus V-I, J-K, and V-K colours. Lebzelter et al. 2012, A&A 547, A108
Variability and atmospheric
structure
Animation: Walter Nowotny
Models vs. Observations
Sample of 5 non-variable red giants
and 7 variable AGB stars in 47 Tuc
L, M, [Fe/H] well known
Teff from NIR photometry
Grid of hydrostatic COMARCS spectra and
5 dynamical model atmospheres for C/O=0.48 and 0.25
Investigation of 9 spectral features
Non-variable vs. variable
Results (example)
Lebzelter et al. 2014, A&A in press
Conclusions ( )
Hydrodynamical models fit the observed high-resspectra of LPVs better than hydrostatic models
BUT: none of the nine configurations tested here gave a good fit to the entire observed high-res spectra
A reasonable fit with hydrostatic models is possible forsome of the mildly pulsating stars.
To fit the EWs observed in LPVs with hydrostatic models:Teff (EW)
Results (example)
Lebzelter et al. 2014, A&A in press
Variability and Line strengthsequ.
wid
th [
A]
0
0.2
0.4
0.6
0.8
1
V [mag]4 6 8 10 12 14
Dynamical model
L: 4000 L
C/O: 0.48
Teff: 3500 K period: 200 d
[Fe/H]: -0.7 mass loss: 2E-7 M/yr
Filled dots: Dynamical model
Triangles: R Cas (Mira)
Lebzelter et al. 2010, A&A 517, A6
Lebzelter et al. 2014, A&A in press
A little experiment from 2010
Pre-defined set of stellar parameters:
Teff = 3900 K, log g = 1.3, [Fe/H] = -0.2, x = 2 kms-1, M = 2 M⊙
A little experiment from 2010
High resolution spectra of four cool giant stars (plus some
photometric colours) were provided to various groups
working in the area of spectral synthesis asking them to derive
stellar parameters from the data provided (Teff, log g, [Fe/H]).
6 results using MARCS models
5 results using ATLAS models
1 result from PHOENIX model
1 result from CODEX model
1 result from Tsuji model atmosphere
Various methods, various spectral synthesis codes
Lebzelter et al. 2012, A&A 547, A108