Examinando por Autor "Da Silveira, C.R."

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    Oxygen and zinc abundances in 417 Galactic bulge red giants
    (EDP Sciences, 2018) Da Silveira, C.R.; Barbuy, B.; Friaça, A.C.S.; Hill, V.; Zoccali, M.; Rafelski, M.; Gonzalez, O.A.; Minniti, D.; Renzini, A.; Ortolani, S.
    Context. Oxygen and zinc in the Galactic bulge are key elements for the understanding of the bulge chemical evolution. Oxygen-to-iron abundance ratios provide a most robust indicator of the star formation rate and chemical evolution of the bulge. Zinc is enhanced in metal-poor stars, behaving as an α-element, and its production may require nucleosynthesis in hypernovae. Most of the neutral gas at high redshift is in damped Lyman-alpha systems (DLAs), where Zn is also observed to behave as an α-element. Aims. The aim of this work is the derivation of the α-element oxygen, together with nitrogen, and the iron-peak element zinc abundances in 417 bulge giants, from moderate resolution (R ∼ 22 000) FLAMES-GIRAFFE spectra. For stars in common with a set of UVES spectra with higher resolution (R ∼ 45 000), the data are intercompared. The results are compared with literature data and chemodynamical models. Methods. We studied the spectra obtained for a large sample of red giant stars, chosen to be one magnitude above the horizontal branch, using FLAMES-GIRAFFE on the Very Large Telescope. We computed the O abundances using the forbidden [OI] 6300.3 Å and Zn abundances using the Zn I 6362.34 Å lines. Stellar parameters for these stars were established in a previous work from our group. Results. We present oxygen abundances for 358 stars, nitrogen abundances for 403 stars and zinc abundances were derived for 333 stars. Having oxygen abundances for this large sample adds information in particular at the moderate metallicities of -1.6 < [Fe/H] < -0.8. Zn behaves as an α-element, very similarly to O, Si, and Ca. It shows the same trend as a function of metallicity as the α-elements, i.e., a turnover around [Fe/H] ∼ - 0.6, and then decreasing with increasing metallicity. The results are compared with chemodynamical evolution models of O and Zn enrichment for a classical bulge. DLAs also show an enhanced zinc-to-iron ratio, suggesting they may be enriched by hypernovae. © ESO 2018.
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    Zinc abundances in Galactic bulge field red giants: Implications for damped Lyman- α systems ∗ ∗ ∗
    (EDP Sciences, 2015-08) Barbuy, B.; Friaça, A.C.S.; Da Silveira, C.R.; Hill, V.; Zoccali, M.; Minniti, D.; Renzini, A.; Ortolani, S.; Gómez, A.
    Context. Zinc in stars is an important reference element because it is a proxy to Fe in studies of damped Lyman- systems (DLAs), permitting a comparison of chemical evolution histories of bulge stellar populations and DLAs. In terms of nucleosynthesis, it behaves as an alpha element because it is enhanced in metal-poor stars. Abundance studies in different stellar populations can give hints to the Zn production in different sites. Aims. The aim of this work is to derive the iron-peak element Zn abundances in 56 bulge giants from high resolution spectra. These results are compared with data from other bulge samples, as well as from disk and halo stars, and damped Lyman- systems, in order to better understand the chemical evolution in these environments. Methods. High-resolution spectra were obtained using FLAMES+UVES on the Very Large Telescope. We computed the Zn abundances using the Zn i lines at 4810.53 and 6362.34 We considered the strong depression in the continuum of the Zn i 6362.34 line, which is caused by the wings of the Ca i 6361.79 line suffering from autoionization. CN lines blending the Zn i 6362.34 A line are also included in the calculations. Results. We find [Zn/Fe] = +0.24 ?0.02 in the range a'1.3 < [Fe/H] < a'0.5 and [Zn/Fe] = +0.06 ?0.02 in the range a'0.5 < [Fe/H] < a'0.1, whereas for [Fe/H] ≥ a'0.1, it shows a spread of a'0.60 < [Zn/Fe] < +0.15, with most of these stars having low [Zn/Fe] < 0.0. These low zinc abundances at the high metallicity end of the bulge define a decreasing trend in [Zn/Fe] with increasing metallicities. A comparison with Zn abundances in DLA systems is presented, where a dust-depletion correction was applied for both Zn and Fe. When we take these corrections into account, the [Zn/Fe] vs. [Fe/H] of the DLAs fall in the same region as the thick disk and bulge stars. Finally, we present a chemical evolution model of Zn enrichment in massive spheroids, representing a typical classical bulge evolution. © 2015 ESO.