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Understanding AGB evolution in Galactic bulge stars from high-resolution infrared spectroscopy

Uttenthaler, S.; Blommaert, J. A. D. L.; Wood, P. R.; Lebzelter, T.; Aringer, B.; Schultheis, M. and Ryde, Nils LU (2015) In Monthly Notices of the Royal Astronomical Society 451(2). p.1750-1769
Abstract
An analysis of high-resolution near-infrared spectra of a sample of 45 asymptotic giant branch (AGB) stars towards the Galactic bulge is presented. The sample consists of two subsamples, a larger one in the inner and intermediate bulge, and a smaller one in the outer bulge. The data are analysed with the help of hydrostatic model atmospheres and spectral synthesis. We derive the radial velocity of all stars, and the atmospheric chemical mix ([Fe/H], C/O, C-12/C-13, Al, Si, Ti, and Y) where possible. Our ability to model the spectra is mainly limited by the (in) completeness of atomic and molecular line lists, at least for temperatures down to T-eff approximate to 3100 K. We find that the subsample in the inner and intermediate bulge is... (More)
An analysis of high-resolution near-infrared spectra of a sample of 45 asymptotic giant branch (AGB) stars towards the Galactic bulge is presented. The sample consists of two subsamples, a larger one in the inner and intermediate bulge, and a smaller one in the outer bulge. The data are analysed with the help of hydrostatic model atmospheres and spectral synthesis. We derive the radial velocity of all stars, and the atmospheric chemical mix ([Fe/H], C/O, C-12/C-13, Al, Si, Ti, and Y) where possible. Our ability to model the spectra is mainly limited by the (in) completeness of atomic and molecular line lists, at least for temperatures down to T-eff approximate to 3100 K. We find that the subsample in the inner and intermediate bulge is quite homogeneous, with a slightly subsolar mean metallicity and only few stars with supersolar metallicity, in agreement with previous studies of non-variable M-type giants in the bulge. All sample stars are oxygen-rich, C/O < 1.0. The C/O and carbon isotopic ratios suggest that third dredge-up (3DUP) is absent among the sample stars, except for two stars in the outer bulge that are known to contain technetium. These stars are also more metal-poor than the stars in the intermediate or inner bulge. Current stellar masses are determined from linear pulsation models. The masses, metallicities and 3DUP behaviour are compared to AGB evolutionary models. We conclude that these models are partly in conflict with our observations. Furthermore, we conclude that the stars in the inner and intermediate bulge belong to a more metal-rich population that follows bar-like kinematics, whereas the stars in the outer bulge belong to the metal-poor, spheroidal bulge population. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
stars: AGB and post-AGB, stars: evolution, stars: late-type, Galaxy:, bulge
in
Monthly Notices of the Royal Astronomical Society
volume
451
issue
2
pages
1750 - 1769
publisher
Wiley-Blackwell
external identifiers
  • wos:000360830000049
  • scopus:84938149558
ISSN
1365-2966
DOI
10.1093/mnras/stv1052
language
English
LU publication?
yes
id
168fb265-6bbe-4ef9-b5f7-354d312466cb (old id 8077352)
date added to LUP
2015-10-26 12:07:58
date last changed
2017-05-21 03:27:42
@article{168fb265-6bbe-4ef9-b5f7-354d312466cb,
  abstract     = {An analysis of high-resolution near-infrared spectra of a sample of 45 asymptotic giant branch (AGB) stars towards the Galactic bulge is presented. The sample consists of two subsamples, a larger one in the inner and intermediate bulge, and a smaller one in the outer bulge. The data are analysed with the help of hydrostatic model atmospheres and spectral synthesis. We derive the radial velocity of all stars, and the atmospheric chemical mix ([Fe/H], C/O, C-12/C-13, Al, Si, Ti, and Y) where possible. Our ability to model the spectra is mainly limited by the (in) completeness of atomic and molecular line lists, at least for temperatures down to T-eff approximate to 3100 K. We find that the subsample in the inner and intermediate bulge is quite homogeneous, with a slightly subsolar mean metallicity and only few stars with supersolar metallicity, in agreement with previous studies of non-variable M-type giants in the bulge. All sample stars are oxygen-rich, C/O &lt; 1.0. The C/O and carbon isotopic ratios suggest that third dredge-up (3DUP) is absent among the sample stars, except for two stars in the outer bulge that are known to contain technetium. These stars are also more metal-poor than the stars in the intermediate or inner bulge. Current stellar masses are determined from linear pulsation models. The masses, metallicities and 3DUP behaviour are compared to AGB evolutionary models. We conclude that these models are partly in conflict with our observations. Furthermore, we conclude that the stars in the inner and intermediate bulge belong to a more metal-rich population that follows bar-like kinematics, whereas the stars in the outer bulge belong to the metal-poor, spheroidal bulge population.},
  author       = {Uttenthaler, S. and Blommaert, J. A. D. L. and Wood, P. R. and Lebzelter, T. and Aringer, B. and Schultheis, M. and Ryde, Nils},
  issn         = {1365-2966},
  keyword      = {stars: AGB and post-AGB,stars: evolution,stars: late-type,Galaxy:,bulge},
  language     = {eng},
  number       = {2},
  pages        = {1750--1769},
  publisher    = {Wiley-Blackwell},
  series       = {Monthly Notices of the Royal Astronomical Society},
  title        = {Understanding AGB evolution in Galactic bulge stars from high-resolution infrared spectroscopy},
  url          = {http://dx.doi.org/10.1093/mnras/stv1052},
  volume       = {451},
  year         = {2015},
}