Examinando por Autor "Angeloni, R."
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Ítem The VISTA Variables in the Vía Láctea infrared variability catalogue (VIVA-I)(Oxford University Press, 2020) Lopes, C.; Cross, N.; Catelan, M.; Minniti, D.; Hempel, M.; Lucas, P.; Angeloni, R.; Jablonsky, F.; Braga, V.; Leao, I.; Herpich, F.; Alonso-Garcia, J.High extinction and crowding create a natural limitation for optical surveys towards the central regions of the Milky Way, where the gas and dust are mainly confined. Large-scale near-infrared (IR) surveys of the Galactic plane and bulge are a good opportunity to explore open scientific questions as well as to test our capability to explore future data sets efficiently. Thanks to the VISTA Variables in the Vía Láctea (VVV) ESO public survey, it is now possible to explore a large number of objects in those regions. This paper addresses the variability analysis of all VVV point sources having more than 10 observations in VVVDR4 using a novel approach. In total, the near-IR light curves of 288 378 769 sources were analysed using methods developed in the New Insight Into Time Series Analysis project. As a result, we present a complete sample having 44 998 752 variable star candidates (VVV-CVSC), which include accurate individual coordinates, near-IR magnitudes (Z,Y,J, and Hs), extinctions A(Ks), variability indices, periods, amplitudes, among other parameters to assess the science. Unfortunately, a side effect of having a highly complete sample, is also having a high level of contamination by non-variable (contamination ratio of non-variables to variables is slightly over 10:1). To deal with this, we also provide some flags and parameters that can be used by the community to decrease the number of variable candidates without heavily decreasing the completeness of the sample. In particular, we cross-identified 339 601 of our sources with Simbad and AAVSO data bases, which provide us with information for these objects at other wavelengths. This subsample constitutes a unique resource to study the corresponding near-IR variability of known sources as well as to assess the IR variability related with X-ray and gamma-ray sources. On the other hand, the other ∼99.5 per cent sources in our sample constitutes a number of potentially new objects with variability information for the heavily crowded and reddened regions of the Galactic plane and bulge. The present results also provide an important queryable resource to perform variability analysis and to characterize ongoing and future surveys like TESS and LSST.Ítem The VVV templates project towards an automated classification of VVV light-curves: I. Building a database of stellar variability in the near-infrared(EDP Sciences, 2014-07) Angeloni, R.; Contreras Ramos, R.; Catelan, M.; Dékány, I.; Gran, F.; Alonso-García, J.; Hempel, M.; Navarrete, C.; Andrews, H.; Aparicio, A.; Beamín, J.C.; Berger, C.; Borissova, J.; Contreras Peña, C.; Cunial, A.; De Grijs, R.; Espinoza, N.; Eyheramendy, S.; Eyheramendy, S.; Fiaschi, M.; Hajdu, G.; Han, J.; Hełminiak, K.G.; Hempel, A.; Hidalgo, S.L.; Ita, Y.; Jeon Y., -B; Jordán, A.; Kwon, J.; Lee, J.T.; Martín, E.L.; Masetti, N.; Matsunaga, N.; Milone, A.P.; Minniti, D.; Morelli, L.; Murgas, F.; Nagayama, T.; Navarro, C.; Ochner, P.; Pérez, P.; Pichara, K.; Rojas-Arriagada, A.; Roquette, J.; Saito, R.K.; Siviero, A.; Sohn, J.; Sung, H.-I.; Tamura, M.; Tata, R.; Tomasella, L.; Townsend, B.; Whitelock, P.Context. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey is a variability survey of the Milky Way bulge and an adjacent section of the disk carried out from 2010 on ESO Visible and Infrared Survey Telescope for Astronomy (VISTA). The VVV survey will eventually deliver a deep near-IR atlas with photometry and positions in five passbands (ZYJHKS) and a catalogue of 1−10 million variable point sources – mostly unknown – that require classifications. Aims. The main goal of the VVV Templates Project, which we introduce in this work, is to develop and test the machine-learning algorithms for the automated classification of the VVV light-curves. As VVV is the first massive, multi-epoch survey of stellar variability in the near-IR, the template light-curves that are required for training the classification algorithms are not available. In the first paper of the series we describe the construction of this comprehensive database of infrared stellar variability. Methods. First, we performed a systematic search in the literature and public data archives; second, we coordinated a worldwide observational campaign; and third, we exploited the VVV variability database itself on (optically) well-known stars to gather high-quality infrared light-curves of several hundreds of variable stars. Results. We have now collected a significant (and still increasing) number of infrared template light-curves. This database will be used as a training-set for the machine-learning algorithms that will automatically classify the light-curves produced by VVV. The results of such an auto mated classification will be covered in forthcoming papers of the series.Ítem Updated census of RR Lyrae stars in the globular cluster ω Centauri (NGC 5139)(EDP Sciences, 2015-05) Navarrete, C.; Contreras Ramos, R.; Catelan, M.; Clement, C.M.; Gran, F.; Alonso-García, J.; Angeloni, R.; Hempel, M.; Dékány, I.; Minniti, D.Aims. ω Centauri (NGC 5139) contains many variable stars of different types and, in particular, more than one hundred RR Lyrae stars. This enabled gathering a homogeneous sample (in terms of instrument, image quality, and time coverage) of high-quality near-infrared (NIR) RR Lyrae light curves by performing an extensive time-series campaign aimed at this object. We have conducted a variability survey of ω Cen in the NIR, using ESO's 4.1 m Visible and Infrared Survey Telescope for Astronomy (VISTA). This is the first paper of a series describing our results. Methods. ω Cen was observed using VIRCAM mounted on VISTA. A total of 42 epochs in J and 100 epochs in KS were obtained, distributed over a total timespan of 352 days. Point-spread function photometry was performed using DAOPHOT in the inner and DoPhot in the outer regions of the cluster. Periods of the known variable stars were improved when necessary using an ANOVA analysis. Results. We collected an unprecedented homogeneous and complete NIR catalog of RR Lyrae stars in the field of ω Cen, allowing us to study for the first time all the RR Lyrae stars associated with the cluster, except for four stars that are located far away from the cluster center. We derived membership status, subclassifications between RRab and RRc subtypes, periods, amplitudes, and mean magnitudes for all the stars in our sample. Additionally, four new RR Lyrae stars were discovered, two of which are very likely cluster members. We also discuss here the distribution of ω Cen stars in the Bailey (period-amplitude) diagram. We provide reference lines in this plane for both Oosterhoff Type I (OoI) and Oosterhoff Type II (OoII) components in J and KS. Conclusions. We clarify the status of many (candidate) RR Lyrae stars that have been reported as unclear in previous studies. This includes stars with anomalous positions in the color-magnitude diagram, uncertain periods or/and variability types, and possible field interlopers. We conclude that ω Cen hosts a total of 88 RRab and 101 RRc stars, which makes for a grand total of 189 probable members. We confirm that most RRab stars in the cluster appear to belong to an OoII component, as previously found using visual data. © 2015 ESO.