Chemical Abundances of the S star GZ Peg

The chemical compositions of stars from the Asymptotic Giant Branch are still poorly known due to the low temperatures of their atmospheres and therefore the presence of many molecular transitions hampering the analysis of atomic lines. One way to overcome this difficulty is by the study of lines in regions free from molecular contamination. We have chosen some of those regions to study the chemical abundance of the S-type star GZ Peg. Stellar parameters are derived from spectroscopic analysis and a metallicity of -0.77 dex is found. Chemical abundances of 8 elements are reported and an enhancement of s-process elements is inferred, typical to that of an S-type star.Comment: 5 figures, 3 tables. accepted for publication in the Publications of the Astronomical Society of Australi

Chemical Abundances in Metal-Rich Bulge-like Stars

We have derived chemical abundances for Ca, Ti, Si, Mg, O, Na, Al, Ni, Co and Cr for a sample of stars with peculiar kinematics and probable origin near the bulge. Our sample stars are in the metallicity range = −0.8 ≤ [Fe/H] ≤ +0.6 dex, and have small pericentric distances, Rp ≤ 3.5 kpc, small scale height, with Zmax +0.3 dex. Compared to bulge stars, such elements are deficient in our sample stas. For the iron-peak elements Cr and Ni we have found a slightly overabundant behavior relative to both thin and thick disks distributions in the metal-poor range, and a smooth decreasing trend for [Cr/Fe] for stars in the supersolar regime. [Co/Fe] ratios track the solar value in the metal-poor range, and show an underabundant behavior relative do thin disk stars for metallicities [Fe/H] > 0.0 de

FEROS Abundance Analysis of 21 Bulgelike SMR Stars

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 foun

HD 11397 and HD 14282 - Two new barium stars?

We have performed a detailed abundance analysis of the content of s-process elements of two dwarf stars with suspected overabundace of those elements. Such stars belong to a special kinematic sample of the solar neighborhood, with peculiar kinematics and different chemical abundances when compared to "normal" disk stars. We aim to define if those stars can be identified as barium stars, based on their s-process elements abundances, and their classification, i.e., if they share their chemical profile with strong or mild barium stars. We also intend to shed light on the possible origins of the different kinds of barium stars. Spectra have been taken by using the FEROS spectrograph at the 1.52m telescope of ESO, La Silla. Abundances have been derived for 18 elements, by matching the synthetic profile with the observed spectrum. We have found that HD 11397 shows a mild enhancement for most of the s-process elements as well as for some r-process elements. This star seems to share its abundance profile with the mild Ba-stars. Although showing some slight chemical anomalies for Y, Sr, Mo, and Pb, HD 14282 depicts a chemical pattern similar to the normal stars with slight s-process enhancements.Comment: 11 pages, 5 figure

Lithium abundances in Bulge-like SMR stars

We analyze a sample of 21 super-metal-rich (SMR) stars, using high-resolution échelle spectra obtained with the FEROS Spectrograph at the 1.5m ESO telescope. The metallicities are in the range 0.15 < [Fe/H] < 0.5, 3 of them in common with Pompéia et al. (2002). 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. Lithium abundances of these stars were derived, and their behaviour with effective temperature is show

A SUCESSÃO SECUNDÁRIA DA MATA ATLÂNTICA NA REGIÃO DE CUBATÃO - SP

Trata-se de uma análise do processo de sucessão secundária de uma capoeira, em área da Mata Atlântica, que sobrevive sob impacto direto da poluição atmosféri­ca, advinda do Pólo Industrial de Cubatão. Durante quatro anos de acompanhamento em campo, verificou­ se uma discreta diminuição no número de espécies pioneiras e secundárias, em função da morte de alguns indivíduos debilitados pela poluição, enquanto as de sub­-bosque tiveram um aumento de indivíduos. As trocas de recrutamento e mortalidade foram as mesmas, girando em torno de 18%. Conclui-se que, embora não ocorra o aumento da densidade de árvores e apesar de sofrer constante "stress" causado pela poluição, a comunidade encontra-se em sucessão, o que é confirmado pelo o aumento da diversidade e biomassa e o surgimento de espécies de sub-bosque e secundárias, como Guarea guidonia, Guapira opposita, Hirtella hebeclada e Hyeronima alchomeoides

Chemical compositions of stars in two stellar streams from the Galactic thick disk

We present abundances for 20 elements for stars in two stellar streams identified by Arifyanto & Fuchs (2006, A&A, 449, 533): 18 stars from the Arcturus stream and 26 from a new stream, which we call AF06 stream, both from the Galactic thick disk. Results show both streams are metal-poor and very old (10$-$14 Gyrs) with kinematics and abundances overlapping with the properties of local field thick disk stars. Both streams exhibit a range in metallicity but with relative elemental abundances that are identical to those of thick disk stars of the same metallicity. These results show that neither stream can result from dissolution of an open cluster. It is highly unlikely that either stream represents tidal debris from an accreted satellite galaxy. Both streams most probably owe their origin to dynamical perturbations within the Galaxy.Comment: 10 figures, Accepted for publication in MNRA

Formation & evolution of the Galactic bulge: constraints from stellar abundances

We compute the chemical evolution of the Galactic bulge in the context of an inside-out model for the formation of the Milky Way. The model contains updated stellar yields from massive stars. The main purpose of the paper is to compare the predictions of this model with new observations of chemical abundance ratios and metallicity distributions in order to put constraints on the formation and evolution of the bulge. We computed the evolution of several alpha-elements and Fe and performed several tests by varying different parameters such as star formation efficiency, slope of the initial mass function and infall timescale. We also tested the effect of adopting a primary nitrogen contribution from massive stars. The [alpha/Fe] abundance ratios in the Bulge are predicted to be supersolar for a very large range in [Fe/H], each element having a different slope. These predictions are in very good agreement with most recent accurate abundance determinations. We also find a good fit of the most recent Bulge stellar metallicity distributions. We conclude that the Bulge formed on a very short timescale (even though timescales much shorter than about 0.1 Gyr are excluded) with a quite high star formation efficiency of about 20 Gyr$^{-1}$ and with an initial mass function more skewed toward high masses (i.e. x <= 0.95) than the solar neighbourhood and rest of the disk. The results obtained here are more robust than previous ones since they are based on very accurate abundance measurements.Comment: 26 pages, 9 figures, accepted for publication in A&

Coincident, 100 kpc-scale damped Lyman alpha absorption towards a binary QSO: how large are galaxies at z ~ 3?

We report coincident damped Lyman alpha (DLA) and sub-DLA absorption at z = 2.66 and z = 2.94 towards the z ~ 3 13.8 arcsecond separation binary quasar SDSS 1116+4118 AB. At the redshifts of the absorbers, this angular separation corresponds to a proper transverse separation of ~ 110 kpc. A third absorber, a sub-DLA at z = 2.47, is detected towards SDSS 1116+4118 B, but no corresponding high column density absorber is present towards SDSS 1116+4118 A. We use high resolution galaxy simulations and a clustering analysis to interpret the coincident absorption and its implications for galaxy structure at z ~ 3. We conclude that the common absorption in the two lines of sight is unlikely to arise from a single galaxy, or a galaxy plus satellite system, and is more feasibly explained by a group of two or more galaxies with separations ~ 100 kpc. The impact of these findings on single line of sight observations is also discussed; we show that abundances of DLAs may be affected by up to a few tenths of a dex by line of sight DLA blending. From a Keck ESI spectrum of the two quasars, we measure metal column densities for all five absorbers and determine abundances for the three absorbers with log N(HI) > 20. For the two highest N(HI) absorbers, we determine high levels of metal enrichment, corresponding to 1/3 and 1/5 solar. These metallicities are amongst the highest measured for DLAs at any redshift and are consistent with values measured in Lyman break galaxies at 2 < z < 3. For the DLA at z = 2.94 we also infer an approximately solar ratio of alpha-to-Fe peak elements from [S/Zn] = +0.05, and measure an upper limit for the molecular fraction in this particular line of sight of log f(H_2)< -5.5.Comment: Accepted for publication in MNRAS. Full resolution simulation images available in pdf copy of the manuscript at http://www.astro.uvic.ca/~sara/1116.pd

The metallicity gradient as a tracer of history and structure : the Magellanic Clouds and M33 galaxies

Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO) DOI: 10.1051/0004-6361/200912138Context. The stellar metallicity and its gradient place constraints on the formation and evolution of galaxies. Aims. This is a study of the metallicity gradient of the LMC, SMC and M33 galaxies derived from their asymptotic giant branch (AGB) stars. Methods. The [Fe/H] abundance was derived from the ratio between C- and M-type AGB stars and its variation analysed as a function of galactocentric distance. Galaxy structure parameters were adopted from the literature. Results. The metallicity of the LMC decreases linearly as −0.047±0.003 dex kpc−1 out to ∼8 kpc from the centre. In the SMC, [Fe/H] has a constant value of ∼−1.25 ± 0.01 dex up to ∼12 kpc. The gradient of the M33 disc, until ∼9 kpc, is −0.078 ± 0.003 dex kpc−1 while the outer disc/halo, out to ∼25 kpc, has [Fe/H] ∼ −1.7 dex. Conclusions. The metallicity of the LMC, as traced by different populations, bears the signature of two major star forming episodes: the first one constituting a thick disc/halo population and the second one a thin disc and bar due to a close encounter with the Milky Way and SMC. The [Fe/H] of the recent episode supports an LMC origin for the Stream. The metallicity of the SMC supports star formation, ∼3 Gyr ago, as triggered by LMC interaction and sustained by the bar in the outer region of the galaxy. The SMC [Fe/H] agrees with the present-day abundance in the Bridge and shows no significant gradient. The metallicity of M33 supports an “insideout” disc formation via accretion of metal poor gas from the interstellar medium.Peer reviewe