Browsing by Author "Alonso-Garcia, J."

Now showing 1 - 6 of 6
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    Discovery of a pair of classical cepheids in an invisible cluster beyond the galactic bulge
    (2015) Dekany, Istvan; Minniti, D.; Hajdu, G.; Alonso-Garcia, J.; Hempel, Maren; Palma, T.; Catelan, Márcio; Gieren Waiblinger, Wolfgang Paul; Majaess, D.
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    Milky Way demographics with the VVV survey: III. Evidence for a great dark lane in the 157 million star bulge color-magnitude diagram
    (2014) Minniti, D.; Saito, R.; Gonzalez, O.; Zoccali, Manuela; Rejkuba, M.; Alonso-Garcia, J.; Benjamin, R.; Catelan, Márcio; Dekany, Istvan; Emerson, J.; Hempel, M.; Lucas, P.; Schultheis, M.
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    RR Lyrae stars in omega Centauri: Near-IR properties and period-luminosity relations
    (2016) Navarrete, C.; Catelan , Marcio; Contreras Ramos, R.; Gran, F.; Alonso-Garcia, J.
    Omega Centauri contains a rich harvest of variable stars. Here we report on a deep, wide-field, near-infrared (IR) variability survey for this cluster, carried out using ESO's 4.1m VISTA telescope. Our time-series data includes more than 180 RR Lyrae light curves in both J and Ks, allowing us to derive an unprecedented homogeneous and complete near-IR catalog of RR Lyrae in the field of omega Cen. Near-IR period-luminosity relations are derived and used to determine an updated (pulsational) distance modulus for the cluster....
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    The VVV Infrared Variability Catalog (VIVA-I)
    (2020) Ferreira Lopes, E. C.; Cross, N. J. G.; Catelan, M.; Minniti, D.; Hempel, M.; Lucas, W. P.; Angeloni, R.; Jablonsky, F.; Braga, F. V.; Leao, C. I.; Herpich, F. R.; Alonso-Garcia, J.; Papageorgiou, A.; Pichara, K.; Saito, K. R.; Bradley, A.; Beamin Muhlenbrock Juan Carlos; Cortes, C.; De Medeiros, J. R.; Russell, Christopher
    Thanks to the VISTA Variables in the Via Lactea (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 (ZYJHKs), 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 de-crease 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 databases, which provide us with information for these objects at other wavelegths. This sub-sample 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% 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.
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    Vista variables in the via lactea (VVV): first results and perspectives
    (2011) Saito, R. K.; Minniti, D.; Dekany, I.; Hempel, M.; Alonso-Garcia, J.; Toledo, I.; Beamin Muhlenbrock, Juan Carlos; Angeloni, R.; Lucas, P. W.; Emerson, J. P.
    VISTA Variables in the Via Lactea (VVV) is a public ESO near-IR variability survey scanning the Milky Way Bulge and an adjacent section of the mid-plane. The survey will take 1929 hours of observations with the 4 m VISTA telescope during five years (2010-2014), covering similar to 10(9) point sources across an area of 520 deg(2). Here we address the first results obtained from the VVV Survey as well as a glimpse into the possibilities for using a deep near-IR atlas in five passbands and a catalogue of more than 10(6) variable point sources. We expect to use the data to find planetary transits of late-type main-sequence stars. We discuss the planet searches and future follow-ups
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    VVVX near-IR photometry for 99 low-mass stars in the Gaia EDR3 Catalog of Nearby Stars
    (2022) Mejias, A.; Minniti, D.; Alonso-Garcia, J.; Beamin Muhlenbrock, Juan Carlos; Saito, R. K.; Solano, E.
    Context. Red dwarf stars, which represent 75% of stars in the Milky Way, can be studied in great detail in the solar neighborhood, where the sample is more complete.Aims. We intend to better characterize red-dwarf candidates selected from the Gaia Catalog of Nearby Stars using optical and near-infrared multi-filter photometry from the Vista Variables in the Via Lactea eXtended (VVVX) Survey, the DECam Plane Survey, the Panoramic Survey Telescope and Rapid Response System, and the Wide-field Infrared Survey Explorer.Methods. We performed a cross-matching procedure among the positions of a color-selected sample of M dwarfs in the VVVX Survey and the Gaia Early Data Release 3 sub-catalog of nearby stars. We explored their stellar parameters and spectral types using the Virtual Observatory SED Analyzer (VOSA). Radii were also obtained from the computed luminosities and T-eff using the Stefan-Boltzmann equation. Masses and ages were computed for some of the objects using evolutionary tracks and isochrones. Additional mass estimations were obtained with the M-Ks - M-* relation. We then validated our results for the stellar parameters of two of our objects with spectra obtained with the TripleSpec instrument at the SOAR telescope, as well as those of our total amount of stars through a direct comparison with an independent sample from the literature. We revised the objects in our sample and compared their proper motion vectors with other sources within 30 '' to identify possible companions and probed their renormalized unit weight error (RUWE) values to identify unresolved companions.Results. We present a catalog of physical parameters for 99 low-mass objects with distances from 43.2 to 111.3 pc. Effective temperatures range from 2500 to 3400 K, with the majority of stars in the sample compatible with the status of M4 dwarfs. We obtained a good agreement between the stellar parameters computed with VOSA and the estimations from observed spectra, also when comparing with an independent sample from the literature. The distribution of masses obtained with VOSA is concentrated toward the very low-mass regime. Eight objects present values of RUWE >= 1.4 and seven are consistent with being part of a binary system.