Examinando por Autor "Minniti, D"
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Ítem Constraining dust extinction properties via the VVV survey(EDP SCIENCES, 2016-09) Majaess, D; Turner, D; Dekany, I; Minniti, D; Gieren, WNear-infrared color-excess and extinction ratios are essential for establishing the cosmic distance scale and probing the Galaxy, particularly when analyzing targets attenuated by significant dust. A robust determination of those ratios followed from leveraging new infrared observations from the VVV survey, wherein numerous bulge RR Lyrae and Type II Cepheids were discovered, in addition to BVJHKs(3.4 -> 22) mu m data for classical Cepheids and O stars occupying the broader Galaxy. The apparent optical color-excess ratios vary significantly with Galactic longitude (l), whereas the near-infrared results are comparatively constant with l and Galactocentric distance (E(J-(3.5 mu m) over bar /E(J - K-s) = 1.28 +/- 0.03. The results derived imply that classical Cepheids and O stars display separate optical trends (R-V,R-BV) with l, which appear to disfavor theories advocating a strict and marked decrease in dust size with increasing Galactocentric distance. The classical Cepheid, Type II Cepheid, and RR Lyrae variables are characterized by (A(J)/E(J-K-s) = (R-J,R-JKs) = 1.49 +/- 0.05 ((A(Ks)/A(J)) = 0.33 +/- 0.02), whereas the O stars are expectedly impacted by emission beyond 3.6 mu m. The mean optical ratios characterizing classical Cepheids and O stars are approximately (R-V,R-BV) similar to 3.1 and (R-V,R-BV) similar to 3.3, respectively.Ítem DISCOVERY OF RR LYRAE STARS IN THE NUCLEAR BULGE OF THE MILKY WAY(IOP PUBLISHING, 2016-10) Minniti, D; Ramos, RC; Zoccali, M; Rejkuba, M; Gonzalez, OA; Valenti, E; Gran, FGalactic nuclei, such as that of the Milky Way, are extreme regions with high stellar densities, and in most cases, the hosts of a supermassive black hole. One of the scenarios proposed for the formation of the Galactic nucleus is merging of primordial globular clusters. An implication of this model is that this region should host stars that are characteristically found in old Milky Way globular clusters. RR Lyrae stars are primary distance indicators, well known representatives of old and metal-poor stellar populations, and therefore are regularly found in globular clusters. Here we report the discovery of a dozen RR Lyrae type ab stars in the vicinity of the Galactic center, i.e., in the so-called nuclear stellar bulge of the Milky Way. This discovery provides the first direct observational evidence that the Galactic nuclear stellar bulge contains ancient stars (>10 Gyr old). Based on this we conclude that merging globular clusters likely contributed to the build-up of the high stellar density in the nuclear stellar bulge of the Milky Way.Ítem Heavy elements Ba, La, Ce, Nd, and Eu in 56 Galactic bulge red giants(EDP SCIENCES, 2016-02) Van der Swaelmen, M; Barbuy, B; Hill, V; Zoccali, M; Minniti, D; Ortolani, S; Gomez, AAims. The aim of this work is the study of abundances of the heavy elements Ba, La, Ce, Nd, and Eu in 56 bulge giants (red giant branch and red clump) with metallicities ranging from 1 : 3 dex to 0 : 5 dex. Methods. We obtained high-resolution spectra of our giant stars using the FLAMES-UVES spectrograph on the Very Large Telescope. We inspected four bulge fields along the minor axis. Results. We measure the chemical evolution of heavy elements, as a function of metallicity, in the Galactic bulge. Conclusions. The [Ba; La; Ce; Nd = Fe] vs. [Fe = H] ratios decrease with increasing metallicity, in which aspect they differ from disc stars. In our metal-poor bulge stars, La and Ba are enhanced relative to their thick disc counterpart, while in our metal-rich bulge stars La and Ba are underabundant relative to their disc counterpart. Therefore, this contrast between bulge and discs trends indicates that bulge and (solar neighbourhood) thick disc stars could behave differently. An increase in left perpendicularLa; Nd = Euright perpendicular with increasing metallicity, for metal-rich stars with [Fe = H] > 0 dex, may indicate that the s-process from AGB stars starts to operate at a metallicity around solar. Finally, [Eu = Fe] follows the [alpha = Fe] behaviour, as expected, since these elements are produced by SNe type II.Ítem Near-infrared photometry of WISE J085510.74-071442.5(EDP SCIENCES, 2016-08) Osorio, MRZ; Lodieu, N; Bejar, VJS; Martin, EL; Ivanov, VD; Bayo, A; Boffin, HMJ; Muzic, K; Minniti, D; Beamin, JCAims. We aim at obtaining near-infrared photometry and deriving the mass, age, temperature, and surface gravity of WISE J085510.74 071442.5 (J0855 0714), which is the coolest object beyond the solar system currently known. Methods. We used publicly available data from the archives of the Hubble Space Telescope (HST) and the Very Large Telescope (VLT) to determine the emission of this source at 1.153 mu m (F110W) and 1.575 mu m (CH4-o ff). J0855 0714 was detected at both wavelengths with a signal-to-noise ratio of approximate to 10 (F110W) and approximate to 4 (CH4-off) at the peak of the corresponding point-spread-functions. Results. This is the first detection of J0855 0714 in the H-band wavelengths. We measured 26.31 +/- 0.10 and 23.22 +/- 0.35 mag in F110W and CH4-o ff (Vega system). J0855 0714 remains unresolved in the HST images that have a spatial resolution of 0.22 0 0. Companions at separations of 0.5 AU (similar mass and brightness) and at similar to 1 AU approximate to 1 mag fainter in the F110W filter) are discarded. By combining the new data with published photometry, including non-detections, we build the spectral energy distribution of J0855 0714 from 0.89 through 22.09 mu m, and contrast it against current solar-metallicity models of planetary atmospheres. We determine that the best spectral fit yields a temperature of 225 250 K, a bolometric luminosity of log L/L-circle dot = 8 : 57, and a high surface gravity of log g = 5 : 0 (cm s(2)), which suggests an old age although a gravity this high is not fully compatible with evolutionary models. After comparing our data with the cooling theory for brown dwarfs and planets, we infer a mass in the interval 2 10 MJup for ages of 1 12 Gyr and high atmospheric gravities of log g greater than or similar to 3.5 (cm s(2)). If it had the age of the Sun, J0855 0714 would be a approximate to 5-M-Jup free-floating planetary-mass object. Conclusions. J0855 0714 meets the mass values previously determined for free-floating planetary-mass objects discovered in starforming regions and young stellar clusters. Based on extrapolations of the substellar mass functions of young clusters to the field, as many J0855 0714-like objects as M5-L2 stars may be expected to populate the solar neighborhood.Ítem The young exoplanetary system TOI-4562: Confirming the presence of a third body in the system(LETTER TO THE EDITOR, 0024-10-09) Fermiano, V; Saito, RK; Ivanov, VD; Caceres, C; Almeida, LA; Aires, J; Beamin, JC; Minniti, D; Ferreira, T; Andrade, L; Borges, BW; de Almeida, L; Jablonski, F; Schlindwein, WYoung planetary systems represent an opportunity to investigate the early stages of (exo)planetary formation because the gravitational interactions have not yet significantly changed the initial configuration of the system. Aims. TOI-4562 b is a highly eccentric temperate Jupiter analogue orbiting a young F7V-type star of < 700 Myr in age with an orbital period of Porb similar to 225 days and an eccentricity of e = 0.76, and is one of the largest known exoplanets to have formed in situ. Methods. We observed a new transit of TOI-4562 b using the 0.6-m Zeiss telescope at the Pico dos Dias Observatory (OPD/LNA) in Minas Gerais, Brazil, and combine our data with Transiting Exoplanet Survey Satellite (TESS) and archive data, with the aim being to improve the ephemerides of this interesting system. Results. The O - C diagram for the new ephemeris is consistent with the presence of a giant planet in an outer orbit around TOI-4562. TOI-4562 c is a planet with a mass of M = 5.77 MJup, an orbital period of Porb = 3990 days, and a semi-major axis of a = 5.219 AU. Conclusions. We report the discovery of TOI-4562 c, the exoplanet with the longest orbital period discovered to date via the transit timing variation (TTV) method. The TOI-4562 system is in the process of violent evolution with intense dynamical changes - judging by its young age and high eccentricity - and is therefore a prime target for studies of formation and evolution of planetary systems.Ítem Variable stars in the Quintuplet stellar cluster with the VVV survey(OXFORD UNIV PRESS, 2016-10) Molina, CN; Borissova, J; Catelan, M; Alonso-Garcia, J; Kerins, E; Kurtev, R; Lucas, PW; Medina, N; Minniti, D; Dekany, IThe Quintuplet cluster is one of the most massive star clusters in the Milky Way, situated very close to the Galactic Centre. We present a new search for variable stars in the vicinity of the cluster, using the five-year data base of the Vista Variables in the Via Lactea (VVV) ESO Public Survey in the near-infrared. A total of 7586 objects were identified in the zone around 2 arcmin from the cluster centre, using 55 K-S-band epochs. 33 stars show K-S-band variability, 24 of them being previously undiscovered. Most of the variable stars found are slow/semiregular variables, long-period variables of the Mira type, and OH/IR stars. In addition, a good number of our candidates show variations in a rather short time-scale. We also propose four young stellar object candidates, which could be cluster members.Ítem VVV-WIT-04: An extragalactic variable source caught by the VVV Survey(Oxford University Press, 2019-11) Saito, R K; Minniti, D; Ivanov, V D; Masetti, N; Navarro, M G; Fernandes, R Cid; Ruschel-Dutra, D; Smith, L C; Lucas, P W; Gonzalez-Fernandez, C; Contreras Ramos, RWe report the discovery of VVV-WIT-04, a near-infrared (near-IR) variable source towards the Galactic disc located ∼0.2 arcsec apart from the position of the radio source PMN J1515−5559. The object was found serendipitously in the near-IR data of the ESO public survey VISTA Variables in the Vía Láctea (VVV). Our analysis is based on variability, multicolour, and proper motion data from VVV and VVV eXtended surveys, complemented with archive data at longer wavelengths. We suggest that VVV-WIT-04 has an extragalactic origin as the near-IR counterpart of PMN J1515−5559. The Ks-band light curve of VVV-WIT-04 is highly variable and consistent with that of an optically violent variable quasar. The variability in the near-IR can be interpreted as the redshifted optical variability. Residuals to the proper motion vary with the magnitude suggesting contamination by a blended source. Alternative scenarios, including a transient event such as a nova or supernova, or even a binary microlensing event, are not in agreement with the available data. © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society