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Li and Be depletion in metal-poor subgiants
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
2006 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 447, no 1, 299-310 p.Article in journal (Refereed) Published
Abstract [en]

A sample of metal-poor subgiants has been observed with the UVES spectrograph at the Very Large Telescope and abundances of Li and Be have been determined. Typical signal-to-noise per spectral bin values for the co-added spectra are of the order of 500 for the line (670.78 nm) and 100 for the doublet lines (313.04 nm). The spectral analysis of the observations was carried out using the Uppsala suite of codes and MARCS (1D-LTE) model atmospheres with stellar parameters from photometry, parallaxes, isochrones and Fe II lines. Abundance estimates of the light elements were corrected for departures from local thermodynamic equilibrium in the line formation. Effective temperatures and Li abundances seem to be correlated and Be abundances correlate with [O/H]. Standard models predict Li and Be abundances approximately one order of magnitude lower than main-sequence values which is in general agreement with the observations. On average, our observed depletions seem to be 0.1 dex smaller and between 0.2 and 0.4 dex larger (depending on which reference is taken) than those predicted for Li and Be, respectively. This is not surprising since the initial Li abundance, as derived from main-sequence stars on the Spite plateau, may be systematically in error by 0.1 dex or more, and uncertainties in the spectrum normalisation and continuum drawing may affect our Be abundances systematically.

Place, publisher, year, edition, pages
2006. Vol. 447, no 1, 299-310 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-92685DOI: 10.1051/0004-6361:20053182OAI: oai:DiVA.org:uu-92685DiVA: diva2:165855
Available from: 2005-02-24 Created: 2005-02-24 Last updated: 2014-01-28Bibliographically approved
In thesis
1. On the Abundances of Li, Be and O in Metal-Poor Stars in the Galaxy
Open this publication in new window or tab >>On the Abundances of Li, Be and O in Metal-Poor Stars in the Galaxy
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Stellar atmospheres constitute excellent environments to study the chemical evolution of our Galaxy. The chemical composition of these atmospheres reflects the composition of the gas from where these stars were born. As the Galaxy evolves, the composition of the gas changes from being primordial (Big-Bang nucleosynthesis) to being enriched in heavy elements (stellar and interstellar nucleosynthesis). The abundances of fragile chemical elements can be affected by stellar mixing processes. Precise lithium, beryllium and oxygen abundance determinations in old stars are presented in this thesis. These determinations are based on the analysis of the observed spectra of a sample of thirteen metal-poor subgiant stars. According to stellar mixing theories, these stars are in a stellar evolutionary stage in which mixing by convection is expected. Abundances of fragile elements like lithium and beryllium are thus expected to be affected by such mixing processes. As a consequence of this, the abundances of these elements are discussed in a dilution context. Lithium and beryllium abundances are compared with the abundances of stars with similar characteristics but in a less evolved stellar phase so that mixing processes have not acted yet. As expected, our abundances seem to be depleted following reasonably well the standard predictions. Stellar abundances of oxygen should give an estimate of the oxygen contribution of core-collapse supernovae to the interstellar medium. However, there is poor agreement among the abundances determined from different atomic or molecular indicators in general. Abundances coming from three different indicators are compared in this thesis. The abundances determined from the O I infrared triplet lines at 777.1-5 nm give the poorest agreement among the three indicators. The abundances based on OH ultraviolet lines around 310 nm are lower for the subgiants in comparison with previous studies of main-sequence stars, becoming even lower than values based on the O I forbidden line at 630.03 nm. Still the most reliable indicator appears to be the O I forbidden line which suggests a plateau-like or only slowly increasing [O/Fe] towards lower [Fe/H]. In addition, the line formation of the Be II ultraviolet resonance lines at 313.0-1 nm, commonly used for abundance determinations purposes, is investigated under non-local thermodynamic equilibrium. We find that the common assumption of local thermodynamic equilibrium typically gives systematic errors of about 0.1 dex.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. vii + 45 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 20
Astronomy, galactic evolution, stellar abundances, stellar atmospheres, spectral line formation, stellar mixing, Astronomi
National Category
Astronomy, Astrophysics and Cosmology
urn:nbn:se:uu:diva-4814 (URN)91-554-6163-8 (ISBN)
Public defence
2005-03-18, Polhemsalen, Ångström Laboratory, Uppsala, 13:15
Available from: 2005-02-24 Created: 2005-02-24Bibliographically approved

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