The Gaia -ESO Survey: Sodium and aluminium abundances in giants and dwarfs: Implications for stellar and Galactic chemical evolution
No hay miniatura disponible
Archivos
Fecha
2016-05
Profesor/a Guía
Facultad/escuela
Idioma
en
Título de la revista
ISSN de la revista
Título del volumen
Editor
EDP Sciences
Nombre de Curso
Licencia CC
Licencia CC
Resumen
Context. Stellar evolution models predict that internal mixing should cause some sodium overabundance at the surface of red giants more massive
than ∼1.5–2.0 M . The surface aluminium abundance should not be affected. Nevertheless, observational results disagree about the presence and/or
the degree of Na and Al overabundances. In addition, Galactic chemical evolution models adopting different stellar yields lead to very different
predictions for the behavior of [Na/Fe] and [Al/Fe] versus [Fe/H]. Overall, the observed trends of these abundances with metallicity are not well
reproduced.
Aims. We readdress both issues, using new Na and Al abundances determined within the Gaia-ESO Survey. Our aim is to obtain better observa tional constraints on the behavior of these elements using two samples: i) more than 600 dwarfs of the solar neighborhood and of open clusters
and ii) low- and intermediate-mass clump giants in six open clusters.
Methods. Abundances were determined using high-resolution UVES spectra. The individual Na abundances were corrected for nonlocal thermo dynamic equilibrium effects. For the Al abundances, the order of magnitude of the corrections was estimated for a few representative cases. For
giants, the abundance trends with stellar mass are compared to stellar evolution models. For dwarfs, the abundance trends with metallicity and age
are compared to detailed chemical evolution models.
Results. Abundances of Na in stars with mass below ∼2.0 M , and of Al in stars below ∼3.0 M , seem to be unaffected by internal mixing
processes. For more massive stars, the Na overabundance increases with stellar mass. This trend agrees well with predictions of stellar evolution ary models. For Al, our only cluster with giants more massive than 3.0 M , NGC 6705, is Al enriched. However, this might be related to the
environment where the cluster was formed. Chemical evolution models that well fit the observed [Na/Fe] vs. [Fe/H] trend in solar neighborhood
dwarfs cannot simultaneously explain the run of [Al/Fe] with [Fe/H], and vice versa. The comparison with stellar ages is hampered by severe
uncertainties. Indeed, reliable age estimates are available for only a half of the stars of the sample. We conclude that Al is underproduced by the
models, except for stellar ages younger than about 7 Gyr. In addition, some significant source of late Na production seems to be missing in the
models. Either current Na and Al yields are affected by large uncertainties, and/or some important Galactic source(s) of these elements has as yet
not been taken into account.
Notas
Indexación: Scopus.
Palabras clave
Galaxy: Abundances, Galaxy: Evolution, Stars: Abundances, Stars: Evolution, Stars: Late-Type
Citación
Astronomy and Astrophysics. Volume 589. 1 May 2016. Article number A115