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

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, ${}^{12}$C/${}^{13}$C, 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 $T_{\mathrm{eff}}\approx 3100$ K. We find that the subsample in the inner and intermediate bulge is quite homogeneous, with a slightly sub-solar mean metallicity and only few stars with super-solar 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.

21 pages, 13 figures, 6 tables (incl. appendix), years of work, published in MNRAS

References in corpus (17)

• Chemical similarities between Galactic bulge and local thick disk red giant stars
• Stellar Proper Motions in the Galactic Bulge from deep HST ACS/WFC Photometry
• Chemical Abundances of Luminous Cool Stars in the Galactic Center from High-Resolution Infrared Spectroscopy
• Helium enrichment and Carbon-star Production in Metal-rich Populations
• Chemical Evolution of the Galactic Bulge as Derived from High-Resolution Infrared Spectroscopy of K and M Red Giants
• The First Detailed Abundances for M giants in the inner Bulge from Infrared Spectroscopy
• The Interplay between Star Formation and the Nuclear Environment of our Galaxy: Deep X-ray Observations of the Galactic Center Arches and Quintuplet Clusters
• The mixed chemistry phenomenon in Galactic Bulge PNe
• Abundances in intermediate-mass AGB stars undergoing third dredge-up and hot-bottom burning
• Clues to the Metallicity Distribution in the Galactic Bulge: Abundances in OGLE-2007_BLG-349S
• Technetium and the third dredge up in AGB stars II. Bulge stars
• Abundances in bulge stars from high-resolution, near-IR spectra I. The CNO elements observed during the science verification of CRIRES at VLT
• Abundances in the Galactic bulge: results from planetary nebulae and giant stars
• Chemical Abundances of M giants in the Galactic Center: a Single Metal-Rich Population with Low [alpha/Fe]
• ISO Mid-Infrared Spectroscopy of Galactic Bulge AGB Stars
• The AGB stars of the intermediate-age LMC cluster NGC 1846 Variability and age determination
• A Catalog of 24um Sources Toward the Galactic Center

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• Clustering of Local Group distances: publication bias or correlated measurements? IV. The Galactic Center
• Chemical evolution of the inner 2 degrees of the Milky Way bulge: [alpha/Fe] trends and metallicity gradients
• Correlations between kinematics and metallicity in the Galactic bulge: a review
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• Stellar Evolution in Real Time: Models Consistent with Direct Observation of Thermal Pulse in T Ursae Minoris
• The Mira-based distance to the Galactic centre
• On the detection of CO and mass loss of Bulge OH/IR stars
• On the chemical abundances of Miras in clusters: V1 in the metal-rich globular NGC 5927
• Long-Period High-Amplitude Red Variables in the KELT Survey