Browsing by Author "da Silva, P."

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    Abundances of iron-peak elements in 58 bulge spheroid stars from APOGEE
    (EDP SCIENCES S A, 2024) Barbuy, B.; Friaca, A. C. S.; Ernandes, H.; da Silva, P.; Souza, S. O.; Fernandez-Trincado, J. G.; Cunha, K.; Smith, V. V.; Masseron, T.; Perez-Villegas, A.; Chiappini, C.; Queiroz, A. B. A.; Santiago, B. X.; Beers, T. C.; Anders, F.; Schiavon, R. P.; Valentini, M.; Minniti, D.; Geisler, D.; Souto, D.; Placco, V. M.; Zoccali, Manuela; Feltzing, S.; Schultheis, M.; Nitschelm, C.
    Context. Stars presently identified in the bulge spheroid are probably very old, and their abundances can be interpreted as due to the fast chemical enrichment of the early Galactic bulge. The abundances of the iron-peak elements are important tracers of nucleosynthesis processes, in particular oxygen burning, silicon burning, the weak s-process, and alpha-rich freeze-out. Aims. The aim of this work is to derive the abundances of V, Cr, Mn, Co, Ni, and Cu in 58 bulge spheroid stars and to compare them with the results of a previous analysis of data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Methods. We selected the best lines for V, Cr, Mn, Co, Ni, and Cu located within the H-band of the spectrum, identifying the most suitable ones for abundance determination, and discarding severe blends. Using the stellar physical parameters available for our sample from the DR17 release of the APOGEE project, we derived the individual abundances through spectrum synthesis. We then complemented these measurements with similar results from different bulge field and globular cluster stars, in order to define the trends of the individual elements and compare with the results of chemical-evolution models. Results. We verify that the H-band has useful lines for the derivation of the elements V, Cr, Mn, Co, Ni, and Cu in moderately metal-poor stars. The abundances, plotted together with others from high-resolution spectroscopy of bulge stars, indicate that: V, Cr, and Ni vary in lockstep with Fe; Co tends to vary in lockstep with Fe, but could be showing a slight decrease with decreasing metallicity; and Mn and Cu decrease with decreasing metallicity. These behaviours are well reproduced by chemical-evolution models that adopt literature yields, except for Cu, which appears to drop faster than the models predict for [Fe/H]<-0.8. Finally, abundance indicators combined with kinematical and dynamical criteria appear to show that our 58 sample stars are likely to have originated in situ.
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    Light elements Na and Al in 58 bulge spheroid stars from APOGEE
    (2023) Barbuy, B.; Friaca, A. C. S.; Ernandes, H.; Moura, T.; Masseron, T.; Cunha, K.; Smith, V. V.; Souto, D.; Perez-Villegas, A.; Souza, S. O.; Chiappini, C.; Queiroz, A. B. A.; Fernandez-Trincado, J. G.; da Silva, P.; Santiago, B. X.; Anders, F.; Schiavon, R. P.; Valentini, M.; Minniti, D.; Geisler, D.; Placco, V. M.; Zoccali, M.; Schultheis, M.; Nitschelm, C.; Beers, T. C.; Razera, R.
    We identified a sample of 58 candidate stars with metallicity [Fe/H]less than or similar to-0.8 that likely belong to the old bulge spheroid stellar population, and analyse their Na and Al abundances from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. In a previous work, we inspected APOGEE-Stellar Parameter and Chemical Abundance Pipeline abundances of C, N, O, Mg, Al, Ca, Si, and Ce in this sample. Regarding Na lines, one of them appears very strong in about 20percent of the sample stars, but it is not confirmed by other Na lines, and can be explained by sky lines, which affect the reduced spectra of stars in a certain radial velocity range. The Na abundances for 15 more reliable cases were taken into account. Al lines in the H band instead appear to be very reliable. Na and Al exhibit a spread in abundances, whereas no spread in N abundances is found, and we found no correlation between them, indicating that these stars could not be identified as second-generation stars that originated in globular clusters. We carry out the study of the behaviour of Na and Al in our sample of bulge stars and literature data by comparing them with chemodynamical evolution model suitable for the Galactic bulge. The Na abundances show a large spread, and the chemodynamical models follow the main data, whereas for aluminum instead, the models reproduce very satisfactorily the nearly secondary-element behaviour of aluminum in the metallicity range below [Fe/H]less than or similar to-1.0. For the lower-metallicity end ([Fe/H<-2.5), hypernovae are assumed to be the main contributor to yields.