* Astronomy

Title: FSR 1716: A new Milky Way Globular Cluster confirmed using VVV RR Lyrae stars
Author: Dante Minniti, Tali Palma, Istvan Dékány, Maren Hempel, Marina Rejkuba, Joyce Pullen, Javier Alonso-García, Rodolfo Barbá, Beatriz Barbuy, Eduardo Bica, Charles Bonatto, Jura Borissova, Marcio Catelan, Julio A. Carballo-Bello, Andre Nicolas Chene, Juan J. Clariá, Roger E. Cohen, Rodrigo Contreras-Ramos, Bruno Dias, Jim Emerson, Dirk Froebrich, Anne S.M. Buckner, Douglas Geisler, Oscar A. Gonzalez, Felipe Gran, Gergely Hagdu, Mike Irwin, Valentin D. Ivanov, Radostin Kurtev, Philip W. Lucas, Daniel Majaess, Francesco Mauro, Christian Moni-Bidin, Camila Navarrete, Sebastian Ramírez Alegría, Roberto K. Saito, Elena Valenti, Manuela Zoccali

We use deep multi-epoch near-IR images of the VISTA Variables in the V\'ia L\'actea (VVV) Survey to search for RR Lyrae stars towards 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 >100 sigma detection for this candidate globular cluster, that is centered at equatorial coordinates RAJ2000=16:10:30.0, DECJ2000=-53:44:56; and galactic coordinates l=329.77812, b=-1.59227. The colour-magnitude diagram of this object reveals a well populated red giant branch, with a prominent red clump at Ks=13.35±0.05, and J-Ks=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 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, <P>=0.540 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 AKs=0.38±0.02, and E(J-Ks)=0.72±0.02 mag, respectively, as measured from the RR Lyrae colours and the near-IR colour-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 RG=4.3kpc.

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