Examinando por Autor "Dias, B."
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Ítem A MUSE study of the inner bulge globular cluster Terzan 9: A fossil record in the Galaxy(2019-12) Ernandes, H.; Dias, B.; Barbuy, B; Kamann, S.; Ortolani, S.; Cantelli, E; Bica, E.; Rossi, L; Ortolani, S; Cantelli, E.; Bica, E; Rossi, LContext. Moderately metal-poor inner bulge globular clusters are relics of a generation of long-lived stars that formed in the early Galaxy. Terzan 9, projected at 4°.12 from the Galactic center, is among the most central globular clusters in the Milky Way, showing an orbit which remains confined to the inner 1 kpc. Aims. Our aim is the derivation of the cluster's metallicity, together with an accurate measurement of the mean radial velocity. In the literature, metallicities in the range between-2.0 < [Fe/H] < -1.0 have been estimated for Terzan 9 based on color-magnitude diagrams and CaII triplet (CaT) lines. Methods. Given its compactness, Terzan 9 was observed using the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope. The extraction of spectra from several hundreds of individual stars allowed us to derive their radial velocities, metallicities, and [Mg/Fe]. The spectra obtained with MUSE were analysed through full spectrum fitting using the ETOILE code. Results. We obtained a mean metallicity of [Fe/H] ≈ -1.10 ±0.15, a heliocentric radial velocity of vhr = 58.1 ± 1.1 km s-1, and a magnesium-To-iron [Mg/Fe] = 0.27 ± 0.03. The metallicity-derived character of Terzan 9 sets it among the family of the moderately metal-poor Blue Horizontal Branch clusters HP 1, NGC 6558, and NGC 6522. © ESO 2019.Ítem Ca triplet metallicities and velocities for 12 globular clusters toward the galactic bulge(EDP Sciences, 2023-01) Geisler, D.; Parisi, M.C.; Dias, B.; Villanova, S.; Mauro, F.; Saviane, I.; Cohen, R.E.; Moni Bidin C.; Minniti, D.Globular clusters (GCs) are excellent tracers of the formation and early evolution of the Milky Way. The bulge GCs (BGCs) are particularly important because they can reveal vital information about the oldest in situ component of the Milky Way. Aims. Our aim is to derive the mean metallicities and radial velocities for 13 GCs that lie toward the bulge and are generally associated with this component. This region is observationally challenging because of high extinction and stellar density, which hampers optical studies of these and similar BGCs, making most previous determinations of these parameters quite uncertain. Methods. We used near-infrared low-resolution spectroscopy with the FORS2 instrument on the VLT to measure the wavelengths and equivalent widths of the Call triplet (CaT) lines for a number of stars per cluster. We derived radial velocities, ascertained membership, and applied known calibrations to determine metallicities for cluster members, for a mean of 11 members per cluster. Unfortunately, one of our targets, VVV-GC002, which is the closest GC to the Galactic center, turned out not to have any members in our sample. Results. We derive mean cluster RV values to 3 km s~1, and mean metallicities to 0.05 dex. We find general good agreement with previous determinations for both metallicity and velocity. On average, our metallicities are 0.07 dex more metal-rich than those of Harris (2010, arXiv: 1012.3224), with a standard deviation of the difference of 0.25 dex. Our sample has metallicities between -0.21 and -1.64. and the values are distributed between the traditional metal-rich BGC peak near [Fe/H] -0.5 and a more metal-poor peak around [Fe/H] -1.1, which has recently been identified. These latter are candidates for the oldest GCs in the Galaxy, if blue horizontal branches are present, and include BH261, NGC6401, NGC6540, NGC6642, and Terzan9. Finally, Terzan 10 is even more metal- poor. However, dynamically, Terzan 10 is likely an intruder from the halo, possibly associated with the Gaia-Enceladus or Kraken accretion events. Terzan 10 is also confirmed as an Oosterhoff type II GC based on our results. Conclusions. The CaT technique is an excellent method for deriving mean metallicities and velocities for heavily obscured GCs. Our sample provides reliable mean values for these two key properties via spectroscopy of a significant number of members per cluster for this important yet previously poorly studied sample of BGCs. We emphasize that the more metal-poor GCs are excellent candidates for being ancient relics of bulge formation. The lone halo intruder in our sample, Terzan 10. is conspicuous for also having by far the lowest metallicity, and casts doubt on the possibility of any bona fide BGCs at metallicities below about -1.5. © 2023 EDP Sciences. All rights reserved.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 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 New VVV Survey Globular Cluster Candidates in the Milky Way Bulge(Institute of Physics Publishing, 2017-11) Minniti, D.; Geisler, D.; Alonso-Garcia, J.; Palma, T.; Beamin, J.C.; Borissova, J.; Catelan, M.; Clariá, J.J.; Cohen, R.E.; Ramos, R.C.; Dias, B.; Fernández-Trincado, J.G.; Gómez, M.; Hempel, M.; Ivanov, V.D.; Kurtev, R.; Lucas, P.W.; Moni-Bidin, C.; Pullen, J.; Alegria, S.R.; Saito, R.K.; Valenti, E.It is likely that a number of Galactic globular clusters remain to be discovered, especially toward the Galactic bulge. High stellar density combined with high and differential interstellar reddening are the two major problems for finding globular clusters located toward the bulge. We use the deep near-IR photometry of the VISTA Variables in the Via Láctea (VVV) Survey to search for globular clusters projected toward the Galactic bulge, and hereby report the discovery of 22 new candidate globular clusters. These objects, detected as high density regions in our maps of bulge red giants, are confirmed as globular cluster candidates by their color-magnitude diagrams. We provide their coordinates as well as their near-IR color-magnitude diagrams, from which some basic parameters are derived, such as reddenings and heliocentric distances. The color-magnitude diagrams reveal well defined red giant branches in all cases, often including a prominent red clump. The new globular cluster candidates exhibit a variety of extinctions (0.06 < A Ks < 2.77) and distances (5.3 < D < 9.5 kpc). We also classify the globular cluster candidates into 10 metal-poor and 12 metal-rich clusters, based on the comparison of their color-magnitude diagrams with those of known globular clusters also observed by the VVV Survey. Finally, we argue that the census for Galactic globular clusters still remains incomplete, and that many more candidate globular clusters (particularly the low luminosity ones) await to be found and studied in detail in the central regions of the Milky Way.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-II. Structure of star clusters in the Magellanic Clouds periphery(Oxford University Press, 2020-10) Santos, J.F.C.; Maia, F.F.S.; Dias, B.; Kerber, L.D.O.; Piatti, A.E.; Bica, E.; Angelo, M.S.; Minniti, D.; Pérez-Villegas, A.; Roman-Lopes, A.; Westera, P.; Fraga L.We provide a homogeneous set of structural parameters of 83 star clusters located at the periphery of the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC). The clusters' stellar density and surface brightness profiles were built from deep, AO assisted optical images, and uniform analysis techniques. The structural parameters were obtained from King and Elson et al. model fittings. Integrated magnitudes and masses (for a subsample) are also provided. The sample contains mostly low surface brightness clusters with distances between 4.5 and 6.5 kpc and between 1 and 6.5 kpc from the LMC and SMC centres, respectively. We analysed their spatial distribution and structural properties, comparing them with those of inner clusters. Half-light and Jacobi radii were estimated, allowing an evaluation of the Roche volume tidal filling. We found that: (i) for our sample of LMC clusters, the tidal radii are, on average, larger than those of inner clusters from previous studies; (ii) the core radii dispersion tends to be greater for LMC clusters located towards the southwest, with position angles of ∼200° and about ∼5° from the LMC centre, i.e.Those LMC clusters nearer to the SMC; (iii) the core radius evolution for clusters with known age is similar to that of inner clusters; (iv) SMC clusters with galactocentric distances closer than 4 kpc are overfilling; (v) the recent Clouds collision did not leave marks on the LMC clusters' structure that our analysis could reveal. © 2020 The Author(s) Published by Oxford University Press on behalf of the 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.