Examinando por Autor "Braga, Vittorio F."
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Ítem A DECam view of the diffuse dwarf galaxy Crater II – Variable stars(Oxford University Press, 2020-02) Vivas, A. Katherina; Walker, Alistair R.; Martínez-Vazquez, Clara E.; Monelli, Matteo; Bono, Giuseppe; Dorta, Antonio; Nidever, David L.; Fiorentino, Giuliana; Gallart, Carme; Andreuzzi, Gloria; Braga, Vittorio F.; Dall’Ora, Massimo; Olsen, Knut; Stetson, Peter B.Time series observations of a single dithered field centred on the diffuse dwarf satellite galaxy Crater II were obtained with the Dark Energy Camera (DECam) at the 4m Blanco Telescope at Cerro Tololo Inter-American Observatory, Chile, uniformly covering up to two half-light radii. Analysis of the g and i time series results in the identification and characterization of 130 periodic variable stars, including 98 RR Lyrae stars, 7 anomalous Cepheids, and 1 SX Phoenicis star belonging to the Crater II population, and 24 foreground variables of different types. Using the large number of ab-type RR Lyrae stars present in the galaxy, we obtained a distance modulus to Crater II of (m - M)0 = 20.333 ± 0.004 (stat) ± 0.07 (sys). The distribution of the RR Lyrae stars suggests an elliptical shape for Crater II, with an ellipticity of 0.24 and a position angle of 153°. From the RR Lyrae stars, we infer a small metallicity dispersion for the old population of Crater II of only 0.17 dex. There are hints that the most metal-poor stars in that narrow distribution have a wider distribution across the galaxy, while the slightly more metal-rich part of the population is more centrally concentrated. Given the features in the colour-magnitude diagram of Crater II, the anomalous Cepheids in this galaxy must have formed through a binary evolution channel of an old population. © 2019 The Author(s)Ítem Confirmation of a New Metal-poor Globular Cluster in the Galactic Bulge(Institute of Physics Publishing, 2018-10) Minniti, Dante; Schlafly E.F.; Palma, Tali; Clariá, Juan J.; Hempel, Maren; Alonso-García, Javier; Bica, Eduardo; Bonatto, Charles; Braga, Vittorio F.; Clementini, Gisella; Garofalo, Alessia; Gómez, Matías; Ivanov, Valentin D.; Lucas, Phillip W.; Pullen, Joyce; Saito, Roberto K.; Smith, Leigh C.We use deep near-IR photometry of the VISTA Variables in the V'a L'ctea (VVV) Survey and deep DECam Plane Survey (DECaPS) optical photometry to confirm the physical reality of the candidate globular cluster (GC) Minni 22, which is located in the Galactic bulge. This object, which was detected as a high density region in our maps of bulge red giants, is now confirmed as a real GC based on the optical and near-IR color'magnitude diagrams. We also recover three known fundamental mode (ab type) RR Lyrae stars within 2 arcmin of the cluster center. The presence of RR Lyrae stars also seems to confirm Minni 22 as a bonafide old and metal-poor GC. We estimate a cluster reddening E(J - Ks) = 0.6 mag and determine its heliocentric distance D = 7.4 ± 0.3 kpc. The optical and near-IR color'magnitude diagrams reveal well-defined red giant branches in all cases, including a red giant branch bump at Ks = 13.30 ± 0.05 mag. The comparison with theoretical isochrones yields a mean metallicity of [Fe/H] = -1.3 ± 0.3 dex, and age of t ∼ 11.2 Gyr. This is a good example of a new low-luminosity (MV = -6.2 mag) GC found in the central bulge of the Milky Way. After discussing the different ways to confirm the existence of bulge GC candidates, we find that one of the best methods is to use the CMDs from the combination of the DECaPS + VVV photometries. © 2018 The American Astronomical Society. All rights reserved.Ítem Impact of Distance Determinations on Galactic Structure. II. Old Tracers(Springer Netherlands, 2018-08) Kunder, Andrea; Valenti, Elena; Dall’Ora, Massimo; Pietrukowicz, Pawel; Sneden, Chris; Bono, Giuseppe; Braga, Vittorio F.; Ferraro, Iván; Fiorentino, Giuliana; Iannicola, Giacinto; Marconi, Marcella; Martínez-Vázquez, Clara E.; Monelli, Matteo; Musella, Ilaria; Ripepi, Vincenzo; Salaris, Maurizio; Stetson, Peter B.Here we review the efforts of a number of recent results that use old tracers to understand the build up of the Galaxy. Details that lead directly to using these old tracers to measure distances are discussed. We concentrate on the following: (1) the structure and evolution of the Galactic bulge and inner Galaxy constrained from the dynamics of individual stars residing therein; (2) the spatial structure of the old Galactic bulge through photometric observations of RR Lyrae-type stars; (3) the three-dimensional structure, stellar density, mass, chemical composition, and age of the Milky Way bulge as traced by its old stellar populations; (4) an overview of RR Lyrae stars known in the ultra-faint dwarfs and their relation to the Galactic halo; and (5) different approaches for estimating absolute and relative cluster ages. © 2018, Springer Nature B.V.