Examinando por Autor "Barbuy, B."
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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 FSR 1776: A new globular cluster in the Galactic bulge?(EDP Sciences, 2022-01) Dias, B.; Palma, T.; Minniti, D.; Fernández-Trincado, J. G.; Alonso-García, J.; Barbuy, B.; Clariá, J. J.; Gomez, M.; Saito, R. K.Context. Recent near-IR surveys have uncovered a plethora of new globular cluster (GC) candidates towards the Milky Way bulge. These new candidates need to be confirmed as real GCs and properly characterised. Aims. We investigate the physical nature of FSR 1776, a very interesting star cluster projected towards the Galactic bulge. This object was originally classified as an intermediate-age open cluster, and has recently been re-discovered independently and classified as a GC candidate (Minni 23). Firstly, our aim is to confirm its GC nature; secondly, we determine its physical parameters. Methods. The confirmation of the cluster existence is checked using the radial velocity (RV) distribution of a MUSE data cube centred at FSR 1776. The cluster parameters are derived from isochrone fitting to the RV-cleaned colour-magnitude diagrams (CMDs) from visible and near-IR photometry taken from VVV, 2MASS, DECAPS, and Gaia all together. Results. The predicted RV distribution for the FSR 1776 coordinates, considering only contributions from the bulge and disc field stars, is not enough to explain the observed MUSE RV distribution. The extra population (12% of the sample) is FSR 1776 with an average RV of -103.7 ± 0.4 km s-1. The CMDs reveal that it is 10 ± 1 Gyr metal-rich population with [Fe/H]phot ≈ +0.2 ± 0.2, [Fe/H]spec = +0.02 ± 0.01(σ = 0.14 dex), located at the bulge distance of 7.24 ± 0.5 kpc with AV ≈ 1.1 mag. The mean cluster proper motions are (⟨ μα⟩,⟨ μδ⟩) = (-2.3 ± 1.1, -2.6 ± 0.8) mas yr-1. Conclusions. FSR 1776 is an old GC located in the Galactic bulge with a super-solar metallicity, among the highest for a Galactic GC. This is consistent with predictions for the age-metallicity relation of the bulge, being FSR 1776 the probable missing link between typical GCs and the metal-rich bulge field. High-resolution spectroscopy of a larger field of view and deeper CMDs are now required for a full characterisation. © ESO 2022.Ítem Gemini/Phoenix H -band analysis of the globular cluster AL 3(EDP Sciences, 2021-04-01) Barbuy, B.; Ernandes, H.; Souza, S. O.; Razera, R.; Moura, T.; Meléndez, J.; Pérez-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 Å, covering the wavelength range 15 525-15 590 Å. C, N, and O abundances are tentatively derived for the sample stars.Ítem High-resolution abundance analysis of four red giants in the globular cluster NGC 6558(EDP Sciences, 2018-11) Barbuy, B.; Muniz, L.; Ortolani, S.; Ernandes, H.; Dias, B.; Saviane, I.; Kerber, L.; Bica, E.; Pérez-Villegas, A.; Rossi, L.; Held, E.V.Context. NGC 6558 is a bulge globular cluster with a blue horizontal branch (BHB), combined with a metallicity of [Fe/H] â‰-1.0. It is similar to HP 1 and NGC 6522, which could be among the oldest objects in the Galaxy. Element abundances in these clusters could reveal the nature of the first supernovae. Aims. We aim to carry out detailed spectroscopic analysis for four red giants of NGC 6558, in order to derive the abundances of the light elements C, N, O, Na, Al, the α-elements Mg, Si, Ca, Ti, and the heavy elements Y, Ba, and Eu. Methods. High-resolution spectra of four stars with FLAMES-UVES at VLT UT2-Kueyen were analysed. Spectroscopic parameter-derivation was based on excitation and ionization equilibrium of Feâraquo; I and Feâ» II. Results. This analysis results in a metallicity of [Fe/H] =-1.17 ± 0.10 for NGC 6558. We find the expected α-element enhancements in O and Mg with [O/Fe] = +0.40, [Mg/Fe] = +0.33, and low enhancements in Si and Ca. Ti has a moderate enhancement of [Ti/Fe] = +0.22. The r-element Eu appears very enhanced with a mean value of [Eu/Fe] = +0.63. The first peak s-elements Y and Sr are also enhanced, these results have however to be treated with caution, given the uncertainties in the continuum definition; the use of neutral species (Srâraquo; I, Yâ» I), instead of the dominant ionized species is another source of uncertainty. Ba appears to have a solar abundance ratio relative to Fe. Conclusions. NGC 6558 shows an abundance pattern that could be typical of the oldest inner bulge globular clusters, together with the pattern in the similar clusters NGC 6522 and HP 1. They show low abundances of the odd-Z elements Na and Al, and of the explosive nucleosynthesis α-elements Si, Ca, and Ti. The hydrostatic burning α-elements O and Mg are normally enhanced as expected in old stars enriched with yields from core-collapse supernovae, and the iron-peak elements Mn, Cu, Zn show low abundances, which is expected for Mn and Cu, but not for Zn. Finally, the cluster trio NGC 6558, NGC 6522, and HP 1 have relatively high abundances of first-peak heavy elements, variable second-peak element Ba, and the r-element Eu is enhanced. The latter is particularly high in NGC 6558. © 2018 ESO.Ítem High-resolution abundance analysis of red giants in the globular cluster NGC 6522(EDP Sciences, 2014) Barbuy, B.; Chiappini, C.; Cantelli, E.; Depagne, E.; Pignatari, M.; Hirschi, R.; Cescutti, G.; Ortolani, S.; Hill, V.; Zoccali, M.; Minniti, D.; Trevisan, M.; Bica, E.; Gómez, A.Context. The [Sr/Ba] and [Y/Ba] scatter observed in some galactic halo stars that are very metal-poor and in a few individual stars of the oldest known Milky Way globular cluster NGC 6522 have been interpreted as evidence of early enrichment by massive fast-rotating stars (spinstars). Because NGC 6522 is a bulge globular cluster, the suggestion was that not only the very-metal poor halo stars, but also bulge stars at [Fe/H] ~-1 could be used as probes of the stellar nucleosynthesis signatures from the earlier generations of massive stars, but at much higher metallicity. For the bulge the suggestions were based on early spectra available for stars in NGC 6522, with a medium resolution of R ~ 22 000 and a moderate signal-to-noise ratio. Aims. The main purpose of this study is to re-analyse the NGC 6522 stars reported previously by using new high-resolution (R ~ 45 000) and high signal-to-noise spectra (S/N > 100). We aim at re-deriving their stellar parameters and elemental ratios, in particular the abundances of the neutron-capture s-process-dominated elements such as Sr, Y, Zr, La, and Ba, and of the r-element Eu. Methods. High-resolution spectra of four giants belonging to the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. The spectroscopic parameters were derived based on the excitation and ionization equilibrium of Fea i and Fe ii. Results. Our analysis confirms a metallicity [Fe/H] =-0.95 ± 0.15 for NGC 6522 and the overabundance of the studied stars in Eu (with +0.2 < [Eu/Fe] < + 0.4) and alpha-elements O and Mg. The neutron-capture s-element-dominated Sr, Y, Zr, Ba, and La now show less pronounced variations from star to star. Enhancements are in the range 0.0 < [Sr/Fe] < +0.4, +0.23 < [Y/Fe] < +0.43, 0.0 < [Zr/Fe] < +0.4, 0.0 < [La/Fe] < +0.35, and 0.05 < [Ba/Fe] < +0.55. Conclusions. The very high overabundances of [Y/Fe] previously reported for the four studied stars is not confirmed with the new high-quality spectra. The moderate enhancement in [Sr/Fe] previously reported for one of the re-studied stars is confirmed, but the strong enhancements of this ratio for the other two stars are not confirmed. Despite the moderate enhancements found for the neutron-capture s-element-dominated species, none of the four stars studied here show positive values for all [Sr/Ba], [Y/Ba] and [Zr/Ba] ratios. The re-studied stars are now compatible not only with the interpretation that the s-process enhancements in these very old stars are due to spinstars, but also with alternative models such as mass transfer from s-process-rich AGB stars. Note, however, that when our results are interpreted in the context of more extended datasets from the literature, the spinstar scenario still seems to be favoured. © 2014 ESO.Ítem High-resolution abundance analysis of red giants in the metal-poor bulge globular cluster HP 1(EDP SCIENCES, 2016-06) Barbuy, B.; Cantelli, E.; Vemado, A.; Ernandes, H.; Ortolani, S.; Saviane, I.; Bica, E.; Minniti, D.; Dias, B.; Momany, Y.; Hill, V.; Zoccali, M.; Siqueira-Mello, C.Context. The globular cluster HP 1 is projected at only 3.̊33 from the Galactic center. Together with its distance, this makes it one of the most central globular clusters in the Milky Way. It has a blue horizontal branch (BHB) and a metallicity of [Fe/H] ≈ −1.0. This means that it probably is one of the oldest objects in the Galaxy. Abundance ratios can reveal the nucleosynthesis pattern of the first stars as well as the early chemical enrichment and early formation of stellar populations. Aims. High-resolution spectra obtained for six stars were analyzed to derive the abundances of the light elements C, N, O, Na, and Al, the alpha-elements Mg, Si, Ca, and Ti, and the heavy elements Sr, Y, Zr, Ba, La, and Eu. Methods. High-resolution spectra of six red giants that are confirmed members of the bulge globular cluster HP 1 were obtained with the 8 m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. The spectroscopic parameter derivation was based on the excitation and ionization equilibrium of Fe i and Fe ii. Results. We confirm a mean metallicity of [Fe/H] = −1.06 ± 0.10, by adding the two stars that were previously analyzed in HP 1. The alpha-elements O and Mg are enhanced by about +0.3 ≲ [O,Mg/Fe] ≲ +0.5 dex, Si is moderately enhanced with +0.15 ≲ [Si/Fe] ≲ +0.35 dex, while Ca and Ti show lower values of −0.04 ≲ [Ca,Ti/Fe] ≲ +0.28 dex. The r-element Eu is also enhanced with [Eu/Fe] ≈ +0.4, which together with O and Mg is indicative of early enrichment by type II supernovae. Na and Al are low, but it is unclear if Na-O are anticorrelated. The heavy elements are moderately enhanced, with −0.20 < [La/Fe] < +0.43 dex and 0.0 < [Ba/Fe] < +0.75 dex, which is compatible with r-process formation. The spread in Y, Zr, Ba, and La abundances, on the other hand, appears to be compatible with the spinstar scenario or other additional mechanisms such as the weak r-process.Ítem 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.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.Ítem VVVX-Gaia discovery of a low luminosity globular cluster in the Milky Way disk(EDP Sciences, 2020-10) Garro, E.R.; Minniti, D.; Gómez, M.; Alonso-García, J.; Barbá, R.H.; Barbuy, B.; Clariá, J.J.; Chené, A.N.; Dias, B.; Hempel, M.; Ivanov, V.D.; Lucas, P.W.Context. Milky Way globular clusters (GCs) are difficult to identify at low Galactic latitudes because of high differential extinction and heavy star crowding. The new deep near-infrared (IR) images and photometry from the VISTA Variables in the Via Láctea Extended Survey (VVVX) allow us to chart previously unexplored regions. Aims. Our long term aim is to complete the census of Milky Way GCs. The immediate goals are to estimate the astrophysical parameters for the newly discovered GC candidates, measuring their reddenings, extinctions, distances, total luminosities, proper motions, sizes, metallicities, and ages. Methods. We used the near-IR VVVX survey database, in combination with the optical photometry and proper motions (PMs) from Gaia Data Release 2 (DR2), and with the Two Micron All Sky Survey photometry to search for and characterise new GCs within the southern Galactic plane (|b| < 5°). Results. We report the detection of a heretofore unknown Galactic GC at RA = 14:09:00.0; Dec =-65:37:12 (J2000) corresponding to l = 310.828 deg; and b =-3.944 deg in galactic coordinates. We calculate a reddening of E(J-Ks) = (0.3 ± 0.03) mag and an extinction of AKs = (0.15 ± 0.01) mag for this new GC. Its distance modulus and corresponding distance were measured as (m-M) = (15.93 ± 0.03) mag and D = (15.5 ± 1.0) kpc, respectively. We also estimate the metallicity and age by comparison with known GCs and by fitting PARSEC and Dartmouth isochrones, finding [Fe/H] = (-0.70 ± 0.2) dex and t = (11.0 ± 1.0) Gyr. The mean GC PMs from Gaia DR2 are μα∗ = (-4.68 ± 0.47) mas yr-1 and μδ = (-1.34 ± 0.45) mas yr-1. The total luminosity of our cluster is estimated to be MKs = (-7.76 ± 0.5) mag. The core and tidal radii from the radial density profile are rc ∼ 2.1′ (4.6 pc) and rt = 6.5′ (14.6 pc) at the cluster distance. Conclusions. We have found a new low luminosity, old and metal-rich GC, situated in the far side of the Galactic disk at RG = 11.2 kpc from the Galactic centre and at z = 1.0 kpc below the plane. Interestingly, the location, metallicity, and age of this GC are coincident with the Monoceros ring structure. © 2020 ESO.Ítem 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.