Examinando por Autor "Lucas, Philip W."
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Ítem AGN candidates in the VVV near-IR galaxy catalogue(2023-04) Baravalle, Laura D.; Schmidt, Eduardo O.; Victoria Alonso M.; Pichel, Ana; Minniti, Dante; Rodríguez-Kamenetzky, Adriana R.; Masetti, Nicola; Villalon, Carolina; Smith, Leigh C.; Lucas, Philip W.The goal of this work is to search for Active Galactic Nuclei (AGN) in the Galactic disc at very low latitudes with |b| < 2◦. For this, we studied the five sources from the VVV near-infrared (IR) galaxy catalogue that have also WISE counterparts and present variability in the VIrac VAriable Classification Ensemble (VIVACE) catalogue. In the near-IR colour-colour diagrams, these objects have in general redder colours compared to the rest of the sources in the field. In the mid-IR ones, they are located in the AGN region, however, there is a source that presents the highest interstellar extinction and different mid-IR colours to be a young stellar object (YSO). We also studied the source variability using two different statistical methods. The fractional variability amplitude σrms ranges from 12.6 to 33.8, being in concordance with previous results found for type-1 AGNs. The slopes of the light curves are in the range (2.6-4.7) × 10-4 mag d-1, also in agreement with results reported on quasars variability. The combination of all these results suggest that four galaxies are type-1 AGN candidates, whereas the fifth source likely a YSO candidate. © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.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 Mira variables in the Milky Way's nuclear stellar disc: Discovery and classification(Oxford University Press, 2022-11) Sanders, Jason L.; Matsunaga, Noriyuki; Kawata, Daisuke; Smith, Leigh C.; Minniti, Dante; Lucas, Philip W.The properties of the Milky Way's nuclear stellar disc give crucial information on the epoch of bar formation. Mira variables are promising bright candidates to study the nuclear stellar disc, and through their period-age relation dissect its star formation history. We report on a sample of 1782 Mira variable candidates across the central $3\times 3\, \mathrm{deg}2$ of the Galaxy using the multi-epoch infrared VISTA Variables in Via Lactea (VVV) survey. We describe the algorithms employed to select candidate variable stars and then model their light curves using periodogram and Gaussian process methods. By combining with WISE, 2MASS, and other archival photometry, we model the multiband light curves to refine the periods and inspect the amplitude variation between different photometric bands. The infrared brightness of the Mira variables means many are too bright and missed by VVV. However, our sample follows a well-defined selection function as expected from artificial star tests. The multiband photometry is modelled using stellar models with circumstellar dust that characterize the mass-loss rates. We demonstrate how 90 per cent of our sample is consistent with O-rich chemistry. Comparison to period-luminosity relations demonstrates that the bulk of the short period stars are situated at the Galactic Centre distance. Many of the longer period variables are very dusty, falling significantly under the O-rich Magellanic Cloud and solar neighbourhood period-luminosity relations and exhibit high mass-loss rates of. The period distribution appears consistent with the nuclear stellar disc forming ago, although it is not possible to disentangle the relative contributions of the nuclear stellar disc and the contaminating bulge. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Ítem The globular cluster VVV CL002 falling down to the hazardous Galactic centre(EDP Sciences, 2024-03-01) Minniti, Dante; Matsunaga, Noriyuki; Fernández-Trincado, José G.; Otsubo, Shogo; Sarugaku, Yuki; Takeuchi, Tomomi; Katoh, Haruki; Hamano, Satoshi; Ikeda, Yuji; Kawakita, Hideyo; Lucas, Philip W.; Smith, Leigh C.Context. The Galactic centre is hazardous for stellar clusters because of the strong tidal force in action there. It is believed that many clusters were destroyed there and contributed stars to the crowded stellar field of the bulge and the nuclear stellar cluster. However, the development of a realistic model to predict the long-term evolution of the complex inner Galaxy has proven difficult, and observations of surviving clusters in the central region would provide crucial insights into destruction processes. Aims. Among the known Galactic globular clusters, VVV CL002 is the closest to the centre, at 0.4 kpc, but has a very high transverse velocity of 400 km s-1. The nature of this cluster and its impact on Galactic astronomy need to be addressed with spectroscopic follow up. Methods. Here we report the first measurements of its radial velocity and chemical abundance based on near-infrared high-resolution spectroscopy. Results. We find that this cluster has a counter-rotating orbit constrained within 1.0 kpc of the centre, and as close as 0.2 kpc at the perigalacticon, confirming that the cluster is not a passerby from the halo but a genuine survivor enduring the harsh conditions of the tidal forces of the Galactic mill. In addition, its metallicity and α abundance ([α/Fe] ≃ +0.4 and [Fe/H] = -0.54) are similar to those of some globular clusters in the bulge. Recent studies suggest that stars with such α-enhanced stars were more common at 3- 6 kpc from the centre around 10 Gyr ago. Conclusions. We infer that VVV CL002 was formed outside but is currently falling down to the centre, showcasing a real-time event that must have occurred to many clusters a long time ago.Ítem VVV Survey Microlensing: Catalog of Best and Forsaken Events(Institute of Physics Publishing, 2020-04) Navarro, María Gabriela; Ramos, Rodrigo Contreras; Minniti, Dante; Pullen, Joyce; Capuzzo-Dolcetta, Roberto; Lucas, Philip W.We search for microlensing events in the zero-latitude area of the Galactic Bulge using the VVV Survey near-IR data. We have discovered a total sample of N = 630 events within an area covering 20.68 deg2 between the years 2010 and 2015. In this paper, we describe the search and present the data for the final sample, including near-IR magnitudes, colors, and proper motions, as well as the standard microlensing parameters. We use the near-IR color-magnitude and color-color diagrams to select N RC = 290 events with red-clump sources to analyze the extinction properties of the sample in the central region of the Galactic plane. The timescale distribution and its dependence in the longitude axis is presented. The mean timescale decreases as we approach the Galactic minor axis (b = 0ˆ). Finally, we give examples of special microlensing events, such as binaries, short-timescale events, and events with a strong parallax effect. © 2020. The American Astronomical Society. All rights reserved.Ítem VVV-WIT-12 and Its Fashionable Nebula: A 4 yr Long-period Young Stellar Object with a Light Echo?(American Astronomical Society, 2023-11-01) Saito, Roberto K.; Stecklum, Bringfried; Minniti, Dante; Lucas, Philip W.; Guo, Zhen; Smith, Leigh C.; Fraga, Luciano; Navarete, Felipe; Beamín, Juan Carlos; Morris, CalumWe report the serendipitous discovery of VVV-WIT-12, an unusual variable source that seems to induce variability in its surrounding nebula. The source belongs to the rare objects that we call WITs (short for What Is This?) discovered within the VISTA Variables in the Vía Láctea (VVV) survey. VVV-WIT-12 was discovered during a pilot search for light echoes from distant supernovae in the Milky Way using the near-IR images of the VVV survey. This source has an extremely red spectral energy distribution, consistent with a very reddened (A V ∼ 100 mag) long-period variable star (P ∼ 1525 days). Furthermore, it is enshrouded in a nebula that changes brightness and color with time, apparently in sync with the central source variations. The near-IR light curve and complementary follow-up spectroscopy observations are consistent with a variable young stellar object illuminating its surrounding nebula. In this case the source periodic variation along the cycles produces an unprecedented light echo in the different regions of the nebula.