Catálogo de publicaciones - libros

Detailed elemental abundances are now available for several individual stars in the Galaxy’s dwarf satellites (Shetrone . 2001, 2003; Geisler 2005; also see the reviews in this proceedings). A comparison of these abundance ratios to those of stars in the Galaxy can be used to address several questions related to galaxy formation and evolution, as well as stellar nucleosynthesis.

Damped Lyα galaxies provide a sample of young galaxies where chemical abundances can be derived throughout the whole universe with an accuracy comparable to that for the local universe. Despite a large spread in redshift, HI column density and metallicity, DLA galaxies show a remarkable uniformity in the elemental ratios rather suggestive of similar chemical evolution if not of an unique population. These galaxies are characterized by a moderate, if any, enhancement of α-elements over Fepeak elemental abundance with [S/Zn]≈ 0 and [O/Zn]≈ 0.2, rather similarly to the dwarfs galaxies in the Local Group. Nitrogen shows a peculiar behaviour with a bimodal distribution and possibly two plateaux. In particular, the plateau at low N abundances ([N/H] < -3), is not observed in other astrophysical sites and might be evidence for primary N production by massive stars.

We present the first results of CaII triplet observations from VLT/FLAMES for Sculptor, Fornax and Sextans dSphs. For each galaxy, we obtained accurate velocity and metallicity measurements for hundreds of stars out to and beyond the tidal radius. In each case, we find clear evidence for the presence of two distinct stellar components with different spatial distribution and kinematics: the metal rich component is more centrally concentrated and kinematically colder than the metal poor one.

We have performed the chemical analysis of extragalactic carbon stars from VLT/UVES spectra. The derived individual abundances of metals and s-elements as well as the well known distance of the selected stars in the Small Magellanic Cloud and the Sagittarius dwarf galaxies permit us to test current models of stellar evolution and nucleosynthesis during the Asymptotic Giant Branch phase in low metallicity environments.

Observations suggest systematic differences between chemical abundances of stars in satellite galaxies and those in the Milky Way halo. These results are difficult to understand at present in the context of hierarchical structure formation, in which dwarf galaxies are believed to be the building blocks of galaxy formation. In this study, we model the accretion and disruption of dwarf galaxies in a ΛCDM Universe using, in combination, a semi-analytical code and numerical simulations. We conclude that differences between the accretion times of surviving satellites versus stars in the local halo, as well as the effect of feedback processes, may account for the observed differences in the chemical abundance distributions.

We present high resolution abundance analysis of nine stars belonging to three of the five globular clusters (GCs) of the Fornax dwarf galaxy. The spectra were taken with UVES at a resolution of 43 000. We find them to be slightly more metalpoor than what was previously calculated with other methods [1]. Fornax cluster 1 is now the most metal-poor globular cluster ever observed, with a [Fe/H] = −2.6. We find evidence of deep mixing in two stars belonging to cluster 1 and cluster 3. Also, Fornax globular clusters seem to have similar α/Fe ratios relative to Galactic globular clusters, though Ca and Ti may show slightly lower α-enhancement.

We present preliminary iron abundances and α element (Ca, Mg) abundance ratios for a sample of 22 Red Giant Branch (RGB) Stars in the Sagittarius galaxy (Sgr), selected near the RGB-Tip. The sample is representative of the Sgr dominant population. The mean iron abundance is [Fe/H]=-0.49. The α element abundance ratios are slightly subsolar, in agreement with the results recently presented by [2].

We discuss the successes and failures of self-consistent rotating models of main sequence and slightly evolved low-mass stars. We focus in particular on the strongest observational constraints which are the lithium surface abundances and the solar rotation profile deduced from helioseismology. We recall that the hot side of the so-called lithium dip is well explained by hydrodynamical models where the transport of angular momentum is carried out by meridional circulation and shear turbulence. For cooler stars however the transport of angular momentum is dominated by another process. We show that internal gravity waves are the best candidate and we explain how the mass dependence of this mechanism is expected to resolve the enigma of the lithium dip in terms of rotational mixing, forming a coherent picture in main sequence stars of all masses.

We discuss the evidence gathered from helioseismology about considerable mixing below the solar convection zone. The evidence is obtained directly through inversions and also through more subtle, somewhat indirect signatures if mixing.

We comment on a few points about modeling of pre main sequence (PMS) evolution, and try to derive some constraints on the stellar evolution during this phase, in spite of the parametric description of convection. We discuss: : the role of deuterium burning and the choice of the initial starting model, : the results of models in which convection is calibrated using the 2D RHD simulation; : lithium burning and HR diagram location in the models calibrated –or not– on the solar radius. We stress that PMS binaries and lithium depletion in young clusters both point toward very inefficient convection in PMS, and that this result does not seem to be due to the use of local convection models.