Examinando por Autor "Pérez-Villegas A."
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Ítem A deep view of a fossil relic in the Galactic bulge: The Globular Cluster HP 1(Oxford University Press, 2019-04-21) Kerber L.O.; Libralato M.; Souza S.O.; Oliveira R.A.P.; Ortolani S.; Pérez-Villegas A.HP 1 is an α-enhanced and moderately metal-poor bulge globular cluster with a blue horizontal branch. These combined characteristics make it a probable relic of the early star formation in the innermost Galactic regions. Here, we present a detailed analysis of a deep near-infrared (NIR) photometry of HP 1 obtained with the NIR GSAOI + GeMS camera at the Gemini-South telescope. J and K S images were collected with an exquisite spatial resolution (FWHM 1/40.1 arcsec), reaching stars at two magnitudes below the MSTO. We combine our GSAOI data with archival F606W-filter HST ACS/WFC images to compute relative proper motions and select bona fide cluster members. Results from statistical isochrone fits in the NIR and optical-NIR colour-magnitude diagrams indicate an age of 12.8 +0.9-0.8 Gyr, confirming that HP 1 is one of the oldest clusters in the Milky Way. The same fits also provide apparent distance moduli in the K S and V filters in very good agreement with the ones from 11 RR Lyrae stars. By subtracting the extinction in each filter, we recover a heliocentric distance of 6.59 +0.17-0.15 kpc. Furthermore, we refine the orbit of HP 1 using this accurate distance and update and accurate radial velocities (from high-resolution spectroscopy) and absolute proper motions (from Gaia DR2), reaching mean perigalactic and apogalactic distances of 1/40.12 and 1/43 kpc, respectively.Ítem Aluminium-enriched metal-poor stars buried in the inner Galaxy(EDP Sciences, 2020-11) Fernández-Trincado J.G.; Beers T.C.; Minniti D.; Tang B.; Villanova S.; Geisler D.; Pérez-Villegas A.; Vieira K.Stars with higher levels of aluminium and nitrogen enrichment are often key pieces in the chemical makeup of multiple populations in almost all globular clusters (GCs). There is also compelling observational evidence that some Galactic components could be partially built from dissipated GCs. The identification of such stars among metal-poor field stars may therefore provide insight into the composite nature of the Milky Way (MW) bulge and inner stellar halo, and could also reveal other chemical peculiarities. Here, based on APOGEE spectra, we report the discovery of 29 mildly metal-poor ([Fe/H] -0.7) stars with stellar atmospheres strongly enriched in aluminium (Al-rich stars: [Al/Fe] +0.5), well above the typical Galactic levels, located within the solar radius toward the bulge region, which lies in highly eccentric orbits (e 0.6). We find many similarities for almost all of the chemical species measured in this work with the chemical patterns of GCs, and therefore we propose that they have likely been dynamically ejected into the bulge and inner halo from GCs formed in situ and/or GCs formed in different progenitors of known merger events experienced by the MW, such as the Gaia-Sausage-Enceladus and/or Sequoia. © 2020 ESO.Ítem Atypical Mg-poor Milky Way Field Stars with Globular Cluster Second-generation-like Chemical Patterns(Institute of Physics Publishing, 2017-09) Fernández-Trincado J.G.; Zamora O.; Garcia-Hernández D.A.; Souto, Diogo; Dell'Agli F.; Schiavon R.P.; Geisler D.; Tang B.; Villanova S.; Hasselquist, Sten; Mennickent R.E.; Cunha, Katia; Shetrone M.; Prieto, Carlos Allende; Vieira K.; Zasowski G.; Sobeck J.; Hayes C.R.; Majewski S.R.; Placco V.M.; Beers T.C.; Schleicher D.R.G.; Robin A.C.; Mészáros, Sz.; Masseron T.; Pérez, Ana E. Garcia; Anders F.; Meza A.; Alves-Brito A.; Carrera R.; Minniti D.; Lane R.R.; Fernández-Alvar E.; Moreno E.; Pichardo B.; Pérez-Villegas A.; Schultheis M.; Roman-Lopes A.; Fuentes C.E.; Nitschelm C.; Harding P.; Bizyaev D.; Pan K.; Oravetz D.; Simmons A.; Ivans, Inese; Blanco-Cuaresma S.; Hernández J.; Alonso-Garcia J.; Valenzuela O.; Chanamé J.We report the peculiar chemical abundance patterns of 11 atypical Milky Way (MW) field red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). These atypical giants exhibit strong Al and N enhancements accompanied by C and Mg depletions, strikingly similar to those observed in the so-called second-generation (SG) stars of globular clusters (GCs). Remarkably, we find low Mg abundances ([Mg/Fe] < 0.0) together with strong Al and N overabundances in the majority (5/7) of the metal-rich ([Fe/H] -1.0) sample stars, which is at odds with actual observations of SG stars in Galactic GCs of similar metallicities. This chemical pattern is unique and unprecedented among MW stars, posing urgent questions about its origin. These atypical stars could be former SG stars of dissolved GCs formed with intrinsically lower abundances of Mg and enriched Al (subsequently self-polluted by massive AGB stars) or the result of exotic binary systems. We speculate that the stars Mg-deficiency as well as the orbital properties suggest that they could have an extragalactic origin. This discovery should guide future dedicated spectroscopic searches of atypical stellar chemical patterns in our Galaxy, a fundamental step forward to understanding the Galactic formation and evolution. © 2017. The American Astronomical Society. All rights reserved.Ítem The VISCACHA survey - VI. Dimensional study of the structure of 82 star clusters in the Magellanic Clouds(Oxford University Press, 2023-03) Jimena Rodríguez M.; Feinstein C.; Baume G.; Dias B.; Maia F.S.M.; Santos J.F.C.; Kerber L.; Minniti D.; Pérez-Villegas A.; De Bórtoli B.; Parisi M.C.; Oliveira R.A.P.We present a study of the internal structure of 82 star clusters located at the outer regions of the Large Magellanic Cloud and the Small Magellanic Cloud using data of the VISCACHA Survey. Through the construction of the minimum spanning tree, which analyses the relative position of stars within a given cluster, it was possible to characterize the internal structure and explore the fractal or subclustered distribution for each cluster. We computed the parameters m (which is the average length of the connected segments normalized by the area), s (which is the mean points separation in units of cluster radius), and Q (the ratio of these components). These parameters are useful to distinguish between radial, homogeneous, and substructured distributions of stars. The dependence of these parameters with the different characteristics of the clusters, such as their ages and spatial distribution, was also studied. We found that most of the studied clusters present a homogeneous stellar distribution or a distribution with a radial concentration. Our results are consistent with the models, suggesting that more dynamically evolved clusters seem to have larger Q values, confirming previous results from numerical simulations. There also seems to be a correlation between the internal structure of the clusters and their galactocentric distances, in the sense that for both galaxies, the more distant clusters have larger Q values. We also paid particular attention to the effects of contamination by non-member field stars and its consequences finding that field star decontamination is crucial for these kinds of studies. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.