Examinando por Autor "Geisler, Douglas"
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Ítem A Sequoia in the Garden: FSR 1758 - Dwarf Galaxy or Giant Globular Cluster?(Institute of Physics Publishing, 2019-01) H. Barbá, Rodolfo; Minnit, Dante; Geisler, Douglas; Alonso-Garcí, Javier; Hempel, Maren; Monachesi, Antonela; . Arias, Julia I; A. Gómez, FacundoWe present the physical characterization of FSR 1758, a new large, massive object very recently discovered in the Galactic Bulge. The combination of optical data from the 2nd Gaia Data Release and the DECam Plane Survey and near-IR data from the VISTA Variables in the Vía Láctea Extended Survey led to a clean sample of likely members. Based on this integrated data set, position, distance, reddening, size, metallicity, absolute magnitude, and proper motion (PM) of this object are measured. We estimate the following parameters: α = 17:31:12, δ = -39:48:30 (J2000), D = 11.5 ±1.0 kpc, mag, R c = 10 pc, R t = 150 pc, dex, Mi < -8.6 ±1.0, μ α = -2.85 mas yr-1, and μ δ = 2.55 mas yr-1. The nature of this object is discussed. If FRS 1758 is a genuine globular cluster (GC), it is one of the largest in the Milky Way, with a size comparable or even larger than that of ω Cen, being also an extreme outlier in the size versus Galactocentric distance diagram. The presence of a concentration of long-period RR Lyrae variable stars and blue horizontal branch stars suggests that it is a typical metal-poor GC of Oosterhoff type II. Further exploration of a larger surrounding field reveals common PM stars, suggesting either tidal debris or that FRS 1758 is actually the central part of a larger extended structure such as a new dwarf galaxy, tentatively named Scorpius. In either case, this object is remarkable, and its discovery graphically illustrates the possibility of finding other large objects hidden in the Galactic Bulge using future surveys. © 2019. The American Astronomical Society. All rights reserved..Ítem FSR 1716: A New Milky Way Globular Cluster Confirmed Using VVV RR Lyrae Stars(Institute of Physics Publishing, 2017-03) Minniti, Dante; Palma, Tali; Dékány, Istvan; Hempel, Maren; Rejkuba, Marina; Pullen, Joyce; Alonso-García, Javier; Barbá, Rodolfo; Barbuy, Beatriz; Bica, Eduardo; Bonatto, Charles; Borissova, Jura; Catelan, Marcio; Carballo-Bello, Julio A.; Chene, Andre Nicolas; Clariá, Juan José; Cohen, Roger E.; Contreras Ramos, Rodrigo; Dias, Bruno; Emerson, Jim; Froebrich, Dirk; Buckner, Anne S. M.; Geisler, Douglas; Gonzalez, Oscar A.; Gran, Felipe; Hagdu, Gergely; Irwin, Mike; Ivanov, Valentin D.; Kurtev, Radostin; Lucas, Philip W.; Majaess, Daniel; Mauro, Francesco; Moni-Bidin, Christian; Navarrete, Camila; Alegría, Sebastian Ramírez; Saito, Roberto K.; Valenti, Elena; Zoccali, ManuelaWe use deep multi-epoch near-IR images of the VISTA Variables in the Vía Láctea (VVV) Survey to search for RR Lyrae stars toward the Southern Galactic plane. Here, we report the discovery of a group of RR Lyrae stars close together in VVV tile d025. Inspection of the VVV images and PSF photometry reveals that most of these stars are likely to belong to a globular cluster that matches the position of the previously known star cluster FSR 1716. The stellar density map of the field yields a >100σ detection for this candidate globular cluster that is centered at equatorial coordinates R.A.J2000 = 16:10:30.0, decl.J2000 = -53:44:56 and galactic coordinates l = 329.77812, b = -1.59227. The color-magnitude diagram of this object reveals a well-populated red giant branch, with a prominent red clump at K s = 13.35 ±0.05, and J - K s = 1.30 ±0.05. We present the cluster RR Lyrae positions, magnitudes, colors, periods, and amplitudes. The presence of RR Lyrae indicates an old globular cluster, with an age >10 Gyr. We classify this object as an Oosterhoff type I globular cluster, based on the mean period of its RR Lyrae type ab, days, and argue that this is a relatively metal-poor cluster with [Fe/H] = -1.5 ±0.4 dex. The mean extinction and reddening for this cluster are and E(J - K s) = 0.72 ±0.02 mag, respectively, as measured from the RR Lyrae colors and the near-IR color-magnitude diagram. We also measure the cluster distance using the RR Lyrae type ab stars. The cluster mean distance modulus is (m - M)0 = 14.38 ±0.03 mag, implying a distance D = 7.5 ±0.2 kpc and a Galactocentric distance R G = 4.3 kpc. © 2017. The American Astronomical Society. All rights reserved.Ítem The Relationship between Globular Cluster Mass, Metallicity, and Light-element Abundance Variations(Astronomical Journal, 2019) Nataf, David M.; Wyse, Rosemary F. G.; Schiavon, Ricardo P.; Ting, Yuan-Sen; Minniti, Dante; Cohen, Roger E.; Fernández-Trincado, José G.; Geisler, Douglas; Nitschelm, Christian; Frinchaboy, Peter M.We investigate aluminum abundance variations in the stellar populations of globular clusters using both literature measurements of sodium and aluminum and APOGEE measurements of nitrogen and aluminum abundances. For the latter, we show that the Payne is the most suitable of the five available abundance pipelines for our purposes. Our combined sample of 42 globular clusters spans approximately 2 dex in [Fe/H] and 1.5 dex in . We find no fewer than five globular clusters with significant internal variations in nitrogen and/or sodium with little to no corresponding variation in aluminum, and that the minimum present-day cluster mass for aluminum enrichment in metal-rich systems is . We demonstrate that the slopes of the [Al/Fe] versus [Na/Fe] and [Al/Fe] versus [N/Fe] relations for stars without field-like abundances are approximately log-linearly dependent on both the metallicity and the stellar mass of the globular clusters. In contrast, the relationship between [Na/Fe] and [N/Fe] shows no evidence of such dependencies. This suggests that there were (at least) two classes of non-supernova chemical polluters that were common in the early universe, and that their relative contributions within globular clusters somehow scaled with the metallicity and mass of globular clusters. The first of these classes is predominantly responsible for the CNO and NeNa abundance variations, and likewise the second for the MgAl abundance variations. Particularly striking examples of this dichotomy include 47 Tuc and M4. As an auxiliary finding, we argue that abundance variations among Terzan 5 stars are consistent with it being a normal globular cluster.