In this work, we present temperature, surface gravity, metallicity, microturbulence and element abundances, determined from a detailed spectroscopic analysis for a sample of 9 Herbig Ae stars, based on high resolution, high S/N spectra.

New abundances of planetary nebulae located towards the bulge of the Galaxy are derived based on observations made at LNA (Brazil). We present accurate abundances of the elements He, N, S, O, Ar, and Ne for 56 PNe located towards the galactic bulge. The data shows a good agreement with other results in the literature, in the sense that the distribution of the abundances is similar to those works. From the statistical analysis performed, we can suggest a bulge-disk interface at 2.2 kpc for the intermediate mass population, marking therefore the outer border of the bulge and inner border of the disk.

Post-AGB (PAGB) stars are luminous objects of low and intermediate mass in a final and short stage of evolution in the transition between AGB stars and planetary nebulae (PNe). In this work we present a quantitative spectral analysis of some hot PAGBs based on high resolution spectra. The stellar parameters and chemical composition were obtained from the synthesis of non-LTE spectra.

Sulfur abundances are derived for a sample of ten B MS star members of the Orion association. The analysis is based on LTE model atmospheres and non-LTE line formation theory by means of spectrum synthesis analysis of Sii and Siii lines. The abundance distribution obtained for the Orion targets is homogeneous within the errors in the analysis: A(S)=7.15±0.05. This abundance result is in agreement with the solar value and with results for the Orion nebula. The sulfur abundances for Orion combined with previous results for other OB-type stars produce a relatively shallow sulfur abundance gradient with a slope of −0.037±0.012 dex Kpc−1.

We report the spectroscopic analysis of six kinematical members of the Zeta Reticuli Moving Group, one of them for the first time. We confirm the existence of the Group by establishing a common abundance pattern for four kinematical members. High resolution spectra yielded abundances of Si, Ca, Fe, Ni and Ba, and others. Effective temperatures were derived from the excitation & ionization equilibria of Fe lines of four stars. For these, and the remaining two members, temperatures were derived from colors and the fitting of theoretical spectra to the Hα line, and ages and masses were estimated from theoretical HR diagrams. We suggest that the Group is physical being metal-poor and ~6 Gyr old.

Radial gradients of metallicity are supported by observations of different young objects in the Galactic thin disk. The shape of the abundance distributions, however, is not completely constrained. Some works describe the abundance distributions as a function of the Galactocentric distance RG by linear fits with a single slope. On the other hand some analyses of open clusters, cepheids and OB stars suggest a discontinuity in the abundance distributions around RG=10 kpc. In this work we analyse a sample of 13 B stars members of four open clusters located within RG=9-11 kpc in order to better constrain the chemical distribution in this region of the disk.

We present high-resolution spectroscopic measurements of the abundances of the α-like element titanium (Ti) and s-process elements yttrium (Y) and lanthanum (La) for M giant candidates of (a) the Sagittarius (Sgr) dwarf spheroidal + tidal tail system, (b) the Triangulum-Andromeda (TriAnd) Star Cloud, and (c) the Galactic Anticenter Stellar Structure (GASS, or Monoceros Stream). All three systems show abundance patterns unlike the Milky Way but typical of dwarf galaxies. The Sgr system abundance patterns resemble those of the Large Magellanic Cloud. GASS/Mon chemically resembles Sgr but is distinct from TriAnd, a result that does not support previous suggestions that TriAnd is a piece of the Monoceros Stream.

We present chemical abundances obtained by fitting synthetic spectra to the FEROS data of 12 C-J stars, normal and silicate carbon one. The Li and 13C abundance, as well as the s-process elements abundance indicates no evidence of a diferent mechanism of formation between the two kinds of C-J stars. We also studied the α elements, and that suggests a scenario that put the carbon C-R stars as a possible progenitor of the beither C-J stars. We made also available a study of the radial velocity of some stars of the sample calculated at different epochs. That allowed us to make some discussion about the probable binary system of some silicon C-J carbon stars. Based on these abundances and radial velocities, we discuss possible evolutive sequences for the C-J.

We have observed 9 bright metal-poor stars whose kinematics suggest they are members of a stellar stream in the vicinity of the Solar neighborhood. These 9 stars exhibit no star-to-star dispersion in their [X/Fe] ratios for the α and Fe-peak elements, and the neutron-capture elements suggest mild enrichment by the main r-process. The abundance patterns seen in this stream are very similar to those found in the metal-poor globular cluster M15, and the kinematics of M15 are similar to those of the stream, suggesting that these two groups of stars may have shared a common origin.

We present the stellar parameters and lithium abundance for 23 stars of the young stellar association AB Doradus, determined by photometry and spectroscopy. The photometric data was obtained at OPD/LNA and/or from the literature and the spectroscopic data was obtained at La silla/ESO and at OPD/LNA. The parameters were determined using photometric calibrations, line ratios, curves of growth and spectral synthesis. Our results confirm that the selected stars are probably association members, showing an uniform metallicity and lithium depletion consistent with 50 Myears

We present the results of a light element abundance analysis of three solar-type main sequence (MS) dwarfs and three red giant branch (RGB) clump stars in the Hyades open cluster using high-resolution and high signal-to-noise spectroscopy. The CNO abundances of each group (MS or RGB) are in excellent star-to-star agreement and confirm that the giants have undergone first dredge-up mixing. The observed abundances are compared to predictions of a standard stellar model based on the Clemson-American University of Beirut (CAUB) stellar evolution code. The model reproduces the observed evolution of the N and O abundances, as well as the previously derived 12C/13C ratio, but it fails to predict the observed level of 12C depletion in the giants. More tellingly, the sum of the observed giant CNO abundances does not equal that of the dwarfs.

In a recent paper, da Silva et al. (2009), we report results of Li abundance analysis for nine young stellar associations, defined in Torres et al. (2008), from a high-resolution optical spectroscopic survey searching for associations containing young stars (SACY), among optical counterparts of ROSAT All-Sky X-ray sources in the Southern Hemisphere. They have applied a convergence method in the (UVW) velocity space and have determined nine nearby young associations in the sample. As they are young and with different ages, those associations form an interesting laboratory to test the Li depletion theory, as a function of the star age.

From high resolution spectra taken with the spectrograph FIES on the Nordic Optical Telescope, La Palma, we measure abundances of oxygen and α-elements in order to characterize stars which from their dynamical properties are suspected to have originated in disrupted satellites. We find that the chemical composition of investigated stars is homogeneous and distinct from Galactic disk dwarfs, which is providing further evidence of their extragalactic origin.

In this paper we try to determine the properties of different galactic components (2 < r < 12kpc) using radial pulsating stars (RPS stars) as tracers. For RPS stars in Galaxy we use a quasi-seismological inversion method (Post Theoretical Mass Method, PTM) which allows us to determine the mass M and the abundance Z for each star. Based on PTM method and using RPS stars as tracers we could determine the chemical structure and evolution of the Galaxy: abundance gradients and segregation between different evolutionary populations. This method is planned to be extended further using the RPS star observed by the KEPLER space mission.

In the framework of he ESO Large Program “First Stars”, high resolution (R=45000) high S/N ratio spectra have been obtained for a sample of Extremely Metal Poor Stars (EMP stars), 35 giants and 18 turnoff stars. Among them 37 have a very low metallicity: [Fe/H]< −2.9.

We analyze a sample of 21 super-metal-rich (SMR) stars, using high-resolution échelle spectra obtained with the Fiber-fed Extended Range Optical Spectrograph at the 1.5m ESO telescope. The metallicities are in the range 0.07 ≤ [Fe/H] ≤ 0.45, 3 of them in common with Pompéia et al. (2009). Geneva photometry, astrometric data from Hipparcos, and radial velocities from CORAVEL are available for these stars. The peculiar kinematics suggests the thin disk close to the bulge as the probable birthplace of these stars (Grenon 1999). From Hipparcos data, it appears that the turnoff of this population indicates an age of 10-11 Gyr (Grenon 1999). Detailed analysis of the sample stars is carried out, and atmospheric parameters are derived from spectroscopic and photometric determinations. Oxygen abundances of these stars are derived, and [O/Fe] overabundances up to +0.35 are found.

We demonstrate for the first time that gaseous halos of disk galaxies can play a vital role in recycling metal-rich gas ejected from the bulges and thus in promoting the chemical evolution of the disks. Our numerical simulations show that metal-rich bulge winds can be accreted onto the thin disks owing to hydrodynamical interaction between the gaseous ejecta and the gaseous halos. Accordingly, we anticipate that chemical abundances of the inner disk stars are significantly influenced by the enriched winds. About ~1% of gaseous ejecta from the bulges can be accreted onto the middle disk corresponding to the sun's position. We discuss these results in the context of the origin of super metal-rich stars in the solar neighborhood as well as an observed flattening of the abundance gradient in the Galactic disk.

I modeled the pollution of low metallicity (Z=0.001) superbubble Hii regions with the ejecta from single stellar populations of 104−106M⊙ in mass. I found that the He, C, N, and O abundance enhancements in the Hii regions, due to pollution with the enriched winds from Wolf-Rayet stars, are insignificant at 5Myr. The few localized metal enhancements observed so far in resolved extragalactic Hii regions are not associated with superbubbles and remain to be modeled in detail.

Planets typically are considerably more metal-rich than even the most metal-rich stars, one indication that planet formation must differ greatly from star formation. There is general agreement that terrestrial planets form by the collisional accumulation of solids composed of heavy elements in the inner regions of protoplanetary disks. Two competing mechanisms exist for the formation of giant planets, core accretion and disk instability, though hybrid combinations are possible as well. In core accretion, a higher metallicity in the protoplanetary disk leads directly to larger core masses and hence to more gas giant planets. Given the strong correlation of gas giant planets detected by Doppler spectroscopy with stellar metallicity, this has often been taken as proof that core accretion is the mechanism that forms giant planets. Recent work, however, implies that the formation of gas giants by disk instability can be enhanced by higher metallicities, though not as dramatically as for core accretion. In both scenarios, the ongoing accretion of planetesimals by gas giant protoplanets leads to strong enrichments of heavy elements in their gaseous envelopes. Both scenarios also imply that gas giant planets should have significant solid cores, raising questions for gas giant interior models without cores. Exoplanets with large inferred core masses seem likely to have formed by core accretion, while gas giants at distances beyond 20 AU seem more likely to have formed by disk instability. Given the wide variety of exoplanets found to date, it appears that both mechanisms are needed to explain the formation of the known population of giant planets.

Extrasolar planetary host stars are enriched in key planet-building elements. These enrichments have the potential to drastically alter the building blocks available for terrestrial planet formation. Here we report on the combination of dynamical models of late-stage terrestrial planet formation within known extrasolar planetary systems with chemical equilibrium models of the composition of solid material within the disk. This allows us to constrain the bulk elemental composition of extrasolar terrestrial planets. A wide variety of resulting planetary compositions exist, ranging from those that are essentially “Earth-like”, containing metallic Fe and Mg-silicates, to those that are dominated by graphite and SiC. This implies that a diverse range of terrestrial planets are likely to exist within extrasolar planetary systems.