Catálogo de publicaciones - libros

High resolution spectral data of red clump stars towards the NGP have been obtained with the spectrograph Elodie at OHP stars. Nearby Hipparcos red clump stars were also observed. We determine the thin and thick properties: kinematics and chemical abundances in the solar neighbourhood. We estimate the surface mass density of the galactic disk, we also determine the thin and thick disk chemical properties.

Previous works [6,13,5,8,14] already outlined the existence of two distinct stellar populations in the Galactic disk, the thick-disk and the thin-disk stars, based on both kinematical properties, as deduced from Hipparcos measurements, and spectroscopic abundance determinations.

We present CCD photometry in the Johnson V, Kron-Cousins I and Washington system CT passbands for NGC2324, a rich open cluster located near the Galactic anticentre direction. We believe that the high discrepancy in the basic cluster parameters derived in previous studies, particularly in the cluster metal content, warrants their redetermination on the basis of more reliable data.

The astrophysical origins of the element fluorine remain uncertain due in part to the availability of just a small number of abundance results for this element, that has readily observable transitions only in the infrared via vibration-rotation lines of HF. In this paper, we discuss all the available Galactic fluorine abundances to date, and add results for field stars with metallicities between [Fe/H] = -0.5 and -1.0, plus two stars that are members of the Orion association. The fluorine abundances obtained for the young Orion members are found to be in agreement with the trend of [F/O] versus O observed for the disk and they are a good representation of the present day value in the Galactic disk.

Oxygen abundances of a large number of metal-rich stars, with and without known planets, were derived from the forbidden line [O I] 6300 Å, the OI 7771–5 Å triplet and from near-UV OH lines. Non-LTE corrections were calculated and applied to the LTE abundance results derived from the OI 7771–5 Å triplet. Spectral synthesis was performed for several OH lines. Results from different indicators are compared. We study abundance trends in planet host and comparison sample stars. We find for all the indicators that, on average, [O/Fe] clearly decreases with [Fe/H], with significantly negative slopes in all the linear fits.

We present the results from our non-LTE investigation for neutral carbon, which was carried out to remove potential systematic errors in stellar abundance analyses. The calculations were performed for late-type stars and give substantial negative non-LTE abundance corrections. When applied to observations of extremely metal-poor stars, which within the LTE framework seem to suggest a possible [C/O] uprise at low metallicities (Akerman et al. 2004), these improvements will have important implications, enabling us to understand if the standard chemical evolution model is adequate, with no need to invoke signatures by Pop. III stars for the carbon nucleosynthesis.

The aim of this paper is to re-analyze the stars studied by AP04 with a technique which discriminates α-enhanced (Non Solar Scaled Abundance, NSSA) stars from those with Solar Scaled Abundances (SSA) without requiring any assumption about the stellar atmospheric parameter values.

We have investigated the abundance of several chemical elements in two large stellar samples kinematically representative of the thin and the thick disks of the Galaxy. Chemical, kinematical and age data have been collected from high quality sources in the literature. Velocities (U,V,W) have been computed and used to select stars with the highest probability to belong to the thin disk and the thick disk respectively. Our results show that the two disks are chemically well separated. Both exhibit a decline of [α/Fe] with increasing [Fe/H]. A transition between the thin/thick disks stars is observed at 10 Gyr

The single most important parameter which determines the evolution of a star is its mass. Detached eclipsing binaries offer the possibility to determine accurate masses and radii for their components. By studying such systems in open and globular clusters it is possible to determine cluster ages to higher precision than by “traditional” methods, such as main-sequence fitting. We have initiated a programme to study detached eclipsing binaries in old open and globular clusters and determine their masses and radii. This allows direct comparisons with models in the mass, radius plane thereby avoiding the troublesome conversion between model (bolometric luminosity, temperature) and observed (color, apparent luminosity) quantities.

Asymptotic Giant Branch stars contribute significantly to the chemical evolution of their host galaxies. All stars with a main-sequence mass ≤ 8⊙ will return eventually 30-80% of their mass to the interstellar medium. In parallel to the He-burning phase, which follows the original main sequence H-burning, AGB stars are known to produce heavy elements. He-burning is accompanied by a strong neutron flux which in turn breeds heavy nuclei in the so called s-process. Convective mixing of the entire star outside of the degenerate C/O core (dredge-up) ensures, that the s-process produced material becomes part of the outer shells which are being expelled in the mass-loss phase on the AGB. In spite of the importance of this process for understanding chemical evolution precious little observational constraints exist for the various models describing thermo-nuclear evolution. Fully resolved infrared spectroscopy of rotation-vibrational molecular transitions may contribute substantially to a better understanding of the thermo-nuclear evolution.