Examinando por Autor "Souza, S.O."
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Ítem Abundance analysis of APOGEE spectra for 58 metal-poor stars from the bulge spheroid(Oxford University Press, 2022-12-01) Razera, R.; Barbuy, B.; Moura, T.C.; Ernandes, H.; Pérez Villegas, A.; Souza, S.O.; Chiappini, C.; Queiroz, A.B.A.; Anders, F.; Fernández Trincado, J.G.; Friaça, 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 α-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. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Ítem The VISCACHA survey - VII. Assembly history of the Magellanic Bridge and SMC Wing from star clusters(Oxford University Press, 2023-09-01) Oliveira, R.A.P.; Maia, F.F.S.; Barbuy, B.; Dias, B.; Santos, J.F.C.; Souza, S.O.; Kerber, L.O.; Bica, E.; Sanmartim, D.; Quint, B.; Fraga, L.; Armond, T.; Minniti, D.; Parisi, M.C.; Katime Santrich, O.J.; Angelo, M.S.; Perez-Villegas, A.; De Bórtoli, B.J.The formation scenario of the Magellanic Bridge during an encounter between the Large and Small Magellanic Clouds ∼200 Myr ago, as proposed by N-body models, would be imprinted in the chemical enrichment and kinematics of its stars and sites of ongoing star formation along its extension. We present an analysis of 33 Bridge star clusters using photometry obtained with the SOAR 4-m telescope equipped with adaptive optics for the VISCACHA survey. We performed a membership selection and derived self-consistent ages, metallicities, distances, and reddening values via statistical isochrone fitting, as well as tidal radii and integrated masses from structure analysis. Two groups are clearly detected: 13 well-studied clusters older than the Bridge, with 0.5-6.8 Gyr and dex, probably formed in situ. The old clusters follow the overall age and metallicity gradients of the SMC, whereas the younger ones are uniformly distributed along the Bridge. The main results are as follows: (i) we derive ages and metallicities for the first time for 9 and 18 clusters, respectively; (ii) we detect two metallicity dips in the age-metallicity relation of the Bridge at ∼200 Myr and 1.5 Gyr ago for the first time, possibly chemical signatures of the formation of the Bridge and Magellanic Stream; (iii) we estimate a minimum stellar mass for the Bridge of 3-5 × 105 M⊙; (iv) we confirm that all the young Bridge clusters at RA and 15 clusters with < Myr and -0.5 are metal-rich with dex. © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Ítem The VISCACHA survey-IV. the SMC West Halo in 8D(Oxford University Press, 2022-05-01) Dias, B.; Parisi, M.C.; Angelo, M.; Maia, F.; Oliveira, R.A.P.; Souza, S.O.; Kerber, L.O.; Santos, J.F.C.; Perez-Villegas, A.; Sanmartim, D.; Quint, B.; Fraga, L.; Barbuy, B.; Bica, E.; Santrich, O. J. Katime; Hernandez-Jimenez, J.A.; Geisler, D.; Minniti, D.; De Bórtoli, B.J.; Bassino, L.P.; Rocha, J.P.The structure of the Small Magellanic Cloud (SMC) is very complex, in particular in the periphery that suffers more from the interactions with the Large Magellanic Cloud (LMC). A wealth of observational evidence has been accumulated revealing tidal tails and bridges made up of gas, stars, and star clusters. Nevertheless, a full picture of the SMC outskirts is only recently starting to emerge with a 6D phase-space map plus age and metallicity using star clusters as tracers. In this work, we continue our analysis of another outer region of the SMC, the so-called West Halo, and combined it with the previously analysed Northern Bridge. We use both structures to define the Bridge and Counter-bridge trailing and leading tidal tails. These two structures are moving away from each other, roughly in the SMC-LMC direction. The West Halo form a ring around the SMC inner regions that goes up to the background of the Northern Bridge shaping an extended layer of the Counter-bridge. Four old Bridge clusters were identified at distances larger than 8 kpc from the SMC centre moving towards the LMC, which is consistent with the SMC-LMC closest distance of 7.5 kpc when the Magellanic Bridge was formed about 150Myr ago; this shows that the Magellanic Bridge was not formed only by pulled gas, but it also removed older stars from the SMC during its formation. We also found age and metallicity radial gradients using projected distances on sky, which are vanished when we use the real 3D distances. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.