Examinando por Autor "Minnit, Dante"

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    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, Facundo
    We 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..
  • Miniatura
    Ítem
    Search for extra-tidal RR Lyrae stars in Milky Way globular clusters from Gaia DR2
    (Oxford University Press, 2019-02) Kundu, Richa; Minnit, Dante; P. Singh, Harinder
    We used extra-tidal RR Lyrae stars to study the dynamics of Galactic globular clusters and know how effects like dynamical friction and tidal disruption affect these clusters. The Gaia DR2 catalogue for RR Lyrae stars (Clementini et al. 2018) is used along with the proper motions and tidal radii data for the globular clusters compiled from literature. A sample of 56 Galactic globular clusters is analysed. Out of these 56 Galactic globular clusters, only 11 have extra-tidal RR Lyrae stars. However, only two clusters, namely, NGC 3201 and NGC 5024, have enough extra-tidal RR Lyrae stars to draw interesting conclusions. NGC 3201 has 13 extra-tidal RR Lyrae stars which are asymmetrically distributed around its centre with more number of stars in its trailing zone than its leading part. We conclude that these asymmetrical tidal tails are due to the combined effect of tidal disruption and the stripped debris from the cluster. On the other hand, NGC 5024 has five extra-tidal RR Lyrae stars, four of them are concentrated in a region which is at a distance of about three times the tidal radius from its centre. These may be the stars that are being ripped apart from the cluster due to tidal disruption. The presence of these extra-tidal RR Lyrae stars in the clusters can be an indication that more cluster stars are present outside their tidal radii which may be revealed by deep wide field colour-magnitude diagrams of the clusters. © 2018 The Author(s).