Examinando por Autor "Navarrete, C."
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Ítem Bulge RR Lyrae stars in the VVV tile b201(EDP Sciences, 2015-03) Gran, F.; Minniti, D.; Saito, R.K.; Navarrete, C.; Dékány, I.; McDonald, I.; Contreras Ramos, R.; Catelan, M.Context. The VISTA Variables in the Vía Láctea (VVV) Survey is one of the six ESO public surveys currently ongoing at the VISTA telescope on Cerro Paranal, Chile. VVV uses near-IR (ZYJHKs) filters that at present provide photometry to a depth of Ks ∼ 17:0 mag in up to 36 epochs spanning over four years, and aim at discovering more than 106 variable sources as well as trace the structure of the Galactic bulge and part of the southern disk. Aims. A variability search was performed to find RR Lyrae variable stars. The low stellar density of the VVV tile b201, which is centered at (l, b) ∼ (-9°, -9°), makes it suitable to search for variable stars. Previous studies have identified some RR Lyrae stars using optical bands that served to test our search procedure. The main goal is to measure the reddening, interstellar extinction, and distances of the RR Lyrae stars and to study their distribution on the Milky Way bulge. Methods. For each star in the tile with more than 25 epochs (∼90% of the objects down to Ks ∼ 17:0 mag), the standard deviation and x2 test were calculated to identify variable candidates. Periods were determined using the analysis of variance. Objects with periods in the RR Lyrae range of 0:2 ≤ P ≤ 1:2 days were selected as candidate RR Lyrae. They were individually examined to exclude false positives. Results. A total of 1.5 sq deg were analyzed, and we found 39 RR Lyr stars, 27 of which belong to the ab-type and 12 to the c-type. Our analysis recovers all the previously identified RR Lyrae variables in the field and discovers 29 new RR Lyr stars. The reddening and extinction toward all the RRab stars in this tile were derived, and distance estimations were obtained through the period-luminosity relation. Despite the limited amount of RR Lyrae stars studied, our results are consistent with a spheroidal or central distribution around ∼8.1 and ∼8.5 kpc. for either the Cardelli or Nishiyama extinction law. Our analysis does not reveal a stream-like structure. Nevertheless, a larger area must be analyzed to definitively rule out streams. © ESO 2015.Ítem Mapping the outer bulge with RRab stars from the VVV Survey(EDP SCIENCES, 2016-07) Gran, F.; Minniti, D.; Saito, R. K.; Zoccali, M.; Gonzalez, O. A.; Navarrete, C.; Catelan, M.; Contreras Ramos, R.; Elorrieta, F.; Eyheramendy, S.; Jordán, A.Context. The VISTA Variables in the Vía Láctea (VVV) is a near-IR time-domain survey of the Galactic bulge and southern plane. One of the main goals of this survey is to reveal the 3D structure of the Milky Way through their variable stars. In particular, enormous numbers of RR Lyrae stars have been discovered in the inner regions of the bulge (−8° ≲ b ≲ −1°) by optical surveys such as OGLE and MACHO, but leaving an unexplored window of more than ~47 sq deg (−10.0° ≲ ℓ ≲ + 10.7° and − 10.3° ≲ b ≲ −8.0°) observed by the VVV Survey. Aims. Our goal is to characterize the RR Lyrae stars in the outer bulge in terms of their periods, amplitudes, Fourier coefficients, and distances in order to evaluate the 3D structure of the bulge in this area. The distance distribution of RR Lyrae stars will be compared to that of red clump stars, which is known to trace a X-shaped structure, in order to determine whether these two different stellar populations share the same Galactic distribution. Methods. A search for RR Lyrae stars was performed in more than ~47 sq deg at low Galactic latitudes (−10.3° ≲ b ≲ −8.0°). In the procedure the χ2 value and analysis of variance (AoV) statistic methods were used to determine the variability and periodic features of the light curves, respectively. To prevent misclassifications, the analysis was performed only on the fundamental mode RR Lyrae stars (RRab) owing to similarities found in the near-IR light curve shapes of contact eclipsing binaries (W UMa) and first overtone RR Lyrae stars (RRc). On the other hand, the red clump stars of the same analyzed tiles were selected, and cuts in the color-magnitude diagram were applied and the maximum distance restricted to ~20 kpc in order to construct a similar catalog in terms of distances and covered area compared to the RR Lyrae stars. Results. We report the detection of more than 1000 RR Lyrae ab-type stars in the VVV Survey located in the outskirts of the Galactic bulge. A few of them are possibly associated with the Sagittarius Dwarf Spheroidal Galaxy. We calculated colours, reddening, extinction, and distances of the detected RR Lyrae stars in order to determine the outer bulge 3D structure. Our main result is that, at the low galactic latitudes mapped here, the RR Lyrae stars trace a centrally concentrated spheroidal distribution. This is a noticeably different spatial distribution to the one traced by red clump stars known to follow a bar and X-shaped structure. We estimate the completeness of our sample at 80% for Ks ≤ 15 mag.Ítem Near-IR period-luminosity relations for pulsating stars in ω Centauri (NGC 5139)(Astronomy and Astrophysics, 2017-08) Navarrete, C.; Catelan, M.; Contreras Ramos, R.; Alonso-García, J.; Gran, F.; Dékány, I.; Minniti, D.Aims. The globular cluster ω Centauri (NGC 5139) hosts hundreds of pulsating variable stars of different types, thus representing a treasure trove for studies of their corresponding period-luminosity (PL) relations. Our goal in this study is to obtain the PL relations for RR Lyrae and SX Phoenicis stars in the field of the cluster, based on high-quality, well-sampled light curves in the near-infrared (IR). Methods. Observations were carried out using the VISTA InfraRed CAMera (VIRCAM) mounted on the Visible and Infrared Survey Telescope for Astronomy (VISTA). A total of 42 epochs in J and 100 epochs in KS were obtained, spanning 352 days. Point-spread function photometry was performed using DoPhot and DAOPHOT crowded-field photometry packages in the outer and inner regions of the cluster, respectively. Results. Based on the comprehensive catalog of near-IR light curves thus secured, PL relations were obtained for the different types of pulsators in the cluster, both in the J and KS bands. This includes the first PL relations in the near-IR for fundamental-mode SX Phoenicis stars. The near-IR magnitudes and periods of Type II Cepheids and RR Lyrae stars were used to derive an updated true distance modulus to the cluster, with a resulting value of (m-M)0 = 13.708 ± 0.035 ± 0.10 mag, where the error bars correspond to the adopted statistical and systematic errors, respectively. Adding the errors in quadrature, this is equivalent to a heliocentric distance of 5.52 ± 0.27 kpc. © 2017 ESO.Ítem Pulsating stars in ω Centauri. Near-IR properties and period-luminosity relations(EDP Sciences, 2017-09) Navarrete, C.; Catelan, M.; Contreras Ramos, R.; Alonso-García, J.; Gran, F.; Dékány, I.; Minniti, D.ω Centauri (NGC 5139) contains many variable stars of different types, including the pulsating type II Cepheids, RR Lyrae and SX Phoenicis stars. We carried out a deep, wide-field, near-infrared (IR) variability survey of ω Cen, using the VISTA telescope. We assembled an unprecedented homogeneous and complete J and KS near-IR catalog of variable stars in the field of ω Cen. In this paper we compare optical and near-IR light curves of RR Lyrae stars, emphasizing the main differences. Moreover, we discuss the ability of near-IR observations to detect SX Phoenicis stars given the fact that the amplitudes are much smaller in these bands compared to the optical. Finally, we consider the case in which all the pulsating stars in the three different variability types follow a single period-luminosity relation in the near-IR bands.Ítem Stellar streams around the Magellanic Clouds in 4D(Monthly Notices of the Royal Astronomical Society, 2019-03-01) Navarrete, C.; Belokurov, V.; Catelan, M.; Jethwa, P.; Koposov, S. E.; Carballo-Bello, J. A.; Jofre, P.; Erkal, D.; Duffau, S.; Corral-Santana, J. M.We carried out a spectroscopic follow-up programme of the four new stellar stream candidates detected by Belokurov & Koposov in the outskirts of the Large Magellanic Cloud (LMC) using FORS2 (VLT). The medium-resolution spectra were used to measure the line-of-sight velocities, estimate stellar metallicities, and classify stars into Blue Horizontal Branch (BHB) and Blue Straggler (BS) stars. Using the 4-D phase-space information, we attribute approximately one half of our sample to the Magellanic Clouds, while the rest is part of the Galactic foreground. Only two of the four stream candidates are confirmed kinematically. While it is impossible to estimate the exact levels of MW contamination, the phase-space distribution of the entire sample of our Magellanic stars matches the expected velocity gradient for the LMC halo and extends as far as 33 deg (angular separation) or 29 kpc from the LMC centre. Our detections reinforce the idea that the halo of the LMC seems to be larger than previously expected, and its debris can be spread in the sky out to very large separations from the LMC centre. Finally, we provide some kinematic evidence that many of the stars analysed here have likely come from the Small Magellanic Cloud.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.