Catálogo de publicaciones - libros

Galactic open clusters exhibit a range of properties that make them valuable probes of stellar and galactic chemical evolution. Metallicities have been determined for open clusters through a variety of photometric and spectroscopic techniques. The status of available data is reviewed and an overview of what these metallicities reveal about Galactic chemical evolution is given. Although many fewer determinations of elemental abundances in open clusters have been made, they serve as useful indicators of nucleosynthesis in previous generations. The available data suggest that the open clusters present a fairly uniform population similar to that of the disk field stars in the solar neighborhood, even to ages of 10 Gyr. There are intriguing indications that the outermost clusters in the disk deviate from the overall abundance gradient and show enhanced α-elements.

Open clusters (OCs) are important tools both for stellar and for galactic astrophysics, as tests of stellar evolution theory for low and intermediate mass stars and as tracers of the Galactic disk properties. Since old OCs allow us to probe the lifetime of the Milky Way disk, up to about 10 Gyr ago, they can be used to study the disk evolution withtime, and in particular its chemical history.

In this contribution we present the results based on high-resolution spectra of 45 clump stars of the Galactic field. The main atmospheric parameters and abundances of C, C, N, O and other mixing sensitive chemical elements were investigated. Elemental ratios in the sample of field stars are compared to the results available for evolved stars in open clusters and to the theoretical prediction of extra mixing in stellar interiors.

The Milky Way harbours two disks that appear distinct concerning scaleheights, kinematics, and elemental abundance patterns. Recent years have seen a surge of studies of the elemental abundance trends in the disks using high resolution spectroscopy. Here I will review and discuss the currently available data. Special focus will also be put on how we define stars to be members of either disk, and how current models of galaxy formation favour that thick disks are formed from several accreted bodies. The ability for the stellar abundance trends to test such predictions are discussed.

One particular fact that is helping us to understand the mechanisms of planetary formation has to do with the planet host stars themselves. In fact, these were found to have, on average, a metal content higher than the one found in stars without detected planetary companions. In this contribution we will mainly focus on the most recent results on the chemical abundances of planet-host stars, and what kind of constraints they are bringing to the theories of planet formation.

AGB stars, in particular those of types, are excellent laboratories to constraint the theory of stellar structure, evolution and nucleosynthesis. Despite the uncertainties still existing in the chemical analysis of these stars, the determination of the abundances of several key species in their atmospheres (lithium, s-elements, carbon and magnesium isotopic ratios etc.) is an useful tool to test these theories and the mixing processes during the AGB phase. This contribution briefly review some recent advances on this subject.

We present recent advances in the determination of chemical abundances of galactic Planetary Nebulae and discuss implications resulting from the comparison with theoretical predictions. From the analysis of diagrams of abundances of N/O vs He/H, N/O vs N/H and N/O vs O/H we argue that very likely the often used solar photospheric abundance of oxygen of 8.9, in usual units, is overestimated by a factor of 2-3, as suggested by very recent work in the Sun. This would solve an astrophysical problem with the measured abundances in planetaries.

We have performed a detailed abundance analysis of six inactive K-type stars using high-resolution optical spectra. We have used three different techniques and compared the results obtained in order to establish their respective merits and faults. The two spectroscopic methods give consistent results suggesting that non- LTE effects are small, whereas the ‘mixed’ spectroscopic-photometric method leads to photospheric parameters and abundances systematically lower than those obtained with the other two. We have also determined the stars’ positions in H-R diagrams and made a comparison between the gravities derived from the ionization equilibrium of the iron lines and from the evolutionary tracks: the agreement is reasonably good.

[La/Eu] and [Ba/Eu] for a sample of Barium stars were determined in order to evaluate the ratio of abundances of s- and r-elements. The results have been compared to previous work dealing with normal red giants and dwarfs with metallicities in the range -3 < [Fe/H] < +0.3.

Abstract. We discuss new observations of He towards planetary nebulae (PNe) using the Very Large Array (VLA), the 305 m Arecibo telescope, which is now capable of observing the He spectral transition, and the recently commissioned 100 m Green Bank Telescope (GBT).