Browsing by Author "Razera, R."

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    Abundance analysis of APOGEE spectra for 58 metal-poor stars from the bulge spheroid
    (2022) Razera, R.; Barbuy, B.; Moura, T. C.; Ernandes, H.; Perez-Villegas, A.; Souza, S. O.; Chiappini, C.; Queiroz, A. B. A.; Anders, F.; Fernandez-Trincado, J. G.; Friaca, A. C. S.; Cunha, K.; Smith, V. V.; Santiago, B. X.; Schiavon, R. P.; Valentini, M.; Minniti, D.; Schultheis, M.; Geisler, D.; Sobeck, J.; Placco, V. M.; Zoccali, M.
    The central part of the Galaxy hosts a multitude of stellar populations, including the spheroidal bulge stars, stars moved to the bulge through secular evolution of the bar, inner halo, inner thick disc, inner thin disc, as well as debris from past accretion events. We identified a sample of 58 candidate stars belonging to the stellar population of the spheroidal bulge, and analyse their abundances. The present calculations of Mg, Ca, and Si lines are in agreement with the ASPCAP abundances, whereas abundances of C, N, O, and Ce are re-examined. We find normal alpha-element enhancements in oxygen, similar to magnesium, Si, and Ca abundances, which are typical of other bulge stars surveyed in the optical in Baade's Window. The enhancement of [O/Fe] in these stars suggests that they do not belong to accreted debris. No spread in N abundances is found, and none of the sample stars is N-rich, indicating that these stars are not second generation stars originated in globular clusters. Ce instead is enhanced in the sample stars, which points to an s-process origin such as due to enrichment from early generations of massive fast rotating stars, the so-called spinstars.
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    Gemini/Phoenix H-band analysis of the globular cluster AL 3
    (2021) Barbuy, B.; Ernandes, H.; Souza, S. O.; Razera, R.; Moura, T.; Melendez, J.; Perez-Villegas, A.; Zoccali, M.; Minniti, D.; Dias, B.; Ortolani, S.; Bica, E.
    Context. The globular cluster AL 3 is old and located in the inner bulge. Three individual stars were observed with the Phoenix spectrograph at the Gemini South telescope. The wavelength region contains prominent lines of CN, OH, and CO, allowing the derivation of C, N, and O abundances of cool stars.Aims. We aim to derive C, N, O abundances of three stars in the bulge globular cluster AL 3, and additionally in stars of NGC 6558 and HP 1. The spectra of AL 3 allows us to derive the cluster's radial velocity.Methods. For AL 3, we applied a new code to analyse its colour-magnitude diagram. Synthetic spectra were computed and compared to observed spectra for the three clusters.Results. We present a detailed identification of lines in the spectral region centred at 15 555 angstrom, covering the wavelength range 15 525-15 590 angstrom. C, N, and O abundances are tentatively derived for the sample stars.
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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.