Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 0707.1380

Low-mass lithium-rich AGB stars in the Galactic bulge: evidence for Cool Bottom Processing?

Stefan Uttenthaler·Thomas Lebzelter·Sara Palmerini·Maurizio Busso·Bernhard Aringer·Michael T. Lederer
View original source ↗Read source document ↗Export metadata ↓

Abstract

Context: The stellar production of the light element lithium is still a matter of debate. Aims: We report the detection of low-mass, Li-rich Asymptotic Giant Branch (AGB) stars located in the Galactic bulge. Methods: A homogeneous and well-selected sample of low mass, oxygen-rich AGB stars in the Galactic bulge has been searched for the absorption lines of Li. Using spectral synthesis techniques, we determine from high resolution UVES/VLT spectra the Li abundance in four out of 27 sample stars, and an upper limit for the remaining stars. Results: Two stars in our sample have a solar Li abundance or above; these stars seem to be a novelty, since they do not show any s-element enhancement. Two more stars have a Li abundance slightly below solar; these stars do show s-element enhancement in their spectra. Different scenarios which lead to an increased Li surface abundance in AGB stars are discussed. Conclusions: Of the different enrichment scenarios presented, Cool Bottom Processing (CBP) is the most likely one for the Li-rich objects identified here. Self-enrichment by Hot Bottom Burning (HBB) seems very unlikely as all Li-rich stars are below the HBB mass limit. Also, the ingestion of a low mass companion into the stars' envelope is unlikely because the associated additional effects are lacking. Mass transfer from a former massive binary companion is a possible scenario, if the companion produced little s-process elements. A simple theoretical estimation for the Li abundance due to CBP is presented and compared to the observed values.

Explore related subjects

astro-ph

Keep this discovery

BibTeXRIS

Stefan Uttenthaler, Thomas Lebzelter, Sara Palmerini, Maurizio Busso, Bernhard Aringer, Michael T. Lederer. 2007-07-10. Low-mass lithium-rich AGB stars in the Galactic bulge: evidence for Cool Bottom Processing?. https://doi.org/10.1051/0004-6361:20077879

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2014

Modifying gravity with the Aether: an alternative to Dark Matter

There is evidence that Newton and Einstein's theories of gravity cannot explain the dynamics of a universe made up solely of baryons and radiation. To be able to understand the properties of galaxies, clusters of galaxies and the universe on the whole it has become commonplace to invoke the presence of dark matter. An alternative approach is to modify the gravitational field equations to accommodate observations. We propose a new class of gravitational theories in which we add a new degree of freedom, the Aether, in the form of a vector field that is coupled covariantly, but non-minimally, with the space-time metric. We explore the Newtonian and non-Newtonian limits, discuss the conditions for these theories to be consistent and explore their effect on cosmology.

astro-ph↗
arXiv2013

Exploring Topology of the Universe in the Cosmic Microwave Background

We study the effect of global topology of the spatial geometry on the cosmic microwave background (CMB) for closed flat and closed hyperbolic models in which the spatial hypersurface is multiply connected. If the CMB temperature fluctuations were entirely produced at the last scattering, then the large-angle fluctuations would be much suppressed in comparison with the simply connected counterparts which is at variance with the observational data. However, as we shall show in this thesis, for low matter density models the observational constraints are less stringent since a large amount of large-angle fluctuations could be produced at late times. On the other hand, a slight suppression in large-angle temperature correlations in such models explains rather naturally the observed anomalously low quadrupole which is incompatible with the prediction of the "standard" Friedmann-Robertson-Walker-Lemaitre models. Interestingly, moreover, the development in the astronomical observation technology has made it possible to directly explore the imprint of the non-trivial topology by looking for identical objects so called "ghosts" in wide separated directions. For the CMB temperature fluctuations identical patterns would appear on a pair of circles in the sky. Another interesting feature is the non-Gaussianity in the temperature fluctuations. Inhomogeneous and anisotropic Gaussian fluctuations for a particular choice of position and orientation are regarded as non-Gaussian fluctuations for a homogeneous and isotropic ensemble.

astro-ph↗
arXiv2013

No large-angle correlations on the non-Galactic microwave sky

We investigate the angular two-point correlation function of temperature in the WMAP maps. Updating and extending earlier results, we confirm the lack of correlations outside the Galaxy on angular scales greater than about 60 degrees at a level that would occur in 0.025 per cent of realizations of the concordance model. This represents a dramatic increase in significance from the original observations by the COBE-DMR and a marked increase in significance from the first-year WMAP maps. Given the rest of the reported angular power spectrum C_\ell, the lack of large-angle correlations that one infers outside the plane of the Galaxy requires covariance among the C_\ell up to \ell=5. Alternately, it requires both the unusually small (5 per cent of realizations) full-sky large-angle correlations, and an unusual coincidence of alignment of the Galaxy with the pattern of cosmological fluctuations (less than 2 per cent of those 5 per cent). We argue that unless there is some undiscovered systematic error in their collection or reduction, the data point towards a violation of statistical isotropy. The near-vanishing of the large-angle correlations in the cut-sky maps, together with their disagreement with results inferred from full-sky maps, remain open problems, and are very difficult to understand within the concordance model.

astro-ph↗