Browsing by Author "Alonso-Garcia, J."

Now showing 1 - 13 of 13
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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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    H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia
    (2019) Fernandez-Trincado, J. G.; Zamora, O.; Souto, Diogo; Cohen, R. E.; Agli, F. Dell; Garcia-Hernandez, D. A.; Masseron, T.; Schiavon, R. P.; Meszaros, Sz; Cunha, K.; Hasselquist, S.; Shetrone, M.; Schiappacasse Ulloa, J.; Tang, B.; Geisler, D.; Schleicher, D. R. G.; Villanova, S.; Mennickent, R. E.; Minniti, D.; Alonso-Garcia, J.; Manchado, A.; Beers, T. C.; Sobeck, J.; Zasowski, G.; Schultheis, M.; Majewski, S. R.; Rojas-Arriagada, A.; Almeida, A.; Santana, F.; Oelkers, R. J.; Longa-Pena, P.; Carrera, R.; Burgasser, A. J.; Lane, R. R.; Roman-Lopes, A.; Ivans, I. I.; Hearty, F. R.
    We present an elemental abundance analysis of high-resolution spectra for five giant stars spatially located within the innermost regions of the bulge globular cluster NGC 6522 and derive Fe, Mg, Al, C, N, O, Si, and Ce abundances based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, two previously unremarked stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea that NGC 6522 stars are formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary polluters of intra-cluster medium. The peculiar abundance signatures of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522.
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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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    New candidate hypervelocity red clump stars in the inner Galactic bulge
    (2024) Luna, A.; Marchetti, T.; Rejkuba, M.; Leigh, N. W. C.; Alonso-Garcia, J.; Navarro, A. Valenzuela; Minniti, D.; Smith, L. C.
    We search for high-velocity stars in the inner region of the Galactic bulge using a selected sample of red clump stars. Some of those stars might be considered hypervelocity stars (HVSs). Even though the HVSs ejection relies on an interaction with the supermassive black hole (SMBH) at the centre of the Galaxy, there are no confirmed detections of HVSs in the inner region of our Galaxy. With the detection of HVSs, ejection mechanism models can be constrained by exploring the stellar dynamics in the Galactic centre through a recent stellar interaction with the SMBH. Based on a previously developed methodology by our group, we searched with a sample of preliminary data from version 2 of the Vista Variables in the Via Lactea (VVV) Infrared Astrometric Catalogue (VIRAC2) and Gaia DR3 data, including accurate optical and near-infrared proper motions. This search resulted in a sample of 46 stars with transverse velocities larger than the local escape velocity within the Galactic bulge, of which four are prime candidate HVSs with high-proper motions consistent with being ejections from the Galactic centre. Adding to that, we studied a sample of reddened stars without a Gaia DR3 counterpart and found 481 stars with transverse velocities larger than the local escape velocity, from which 65 stars have proper motions pointing out of the Galactic centre and are candidate HVSs. In total, we found 69 candidate HVSs pointing away from the Galactic centre with transverse velocities larger than the local escape velocity.
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    Reinforcing the link between the double red clump and the X-shaped bulge of the Milky Way
    (2015) Gonzalez, O. A.; Zoccali, M.; Debattista, V. P.; Alonso-Garcia, J.; Valenti, E.; Minniti, D.
    The finding of a double red clump in the luminosity function of the Milky Way bulge has been interpreted as evidence for an X-shaped structure. Recently, an alternative explanation has been suggested, where the double red clump is an effect of multiple stellar populations in a classical spheroid. In this Letter we provide an observational assessment of this scenario and show that it is not consistent with the behaviour of the red clump across different lines of sight, particularly at high distances from the Galactic plane. Instead, we confirm that the shape of the red clump magnitude distribution closely follows the distance distribution expected for an X-shaped bulge at critical Galactic latitudes. We also emphasize some key observational properties of the bulge red clump that should not be neglected in the search for alternative scenarios.
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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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    Spectroscopic confirmation of high-amplitude eruptive YSOs and dipping giants from the VVV survey
    (2024) Guo, Zhen; Lucas, P. W.; Kurtev, R.; Borissova, J.; Pena, C. Contreras; Yurchenko, S. N.; Smith, L. C.; Minniti, D.; Saito, R. K.; Bayo, A.; Catelan, M.; Alonso-Garcia, J.; Garatti, A. Caratti o; Morris, C.; Froebrich, D.; Tennyson, J.; Mauco, K.; Aguayo, A.; Miller, N.; Muthu, H. D. S.
    During the pre-main-sequence (pre-MS) evolution stage of a star, significant amounts of stellar mass are accreted during episodic accretion events, such as multidecade FUor-type outbursts. Here, we present a near-infrared spectroscopic follow-up study of 33 high-amplitude (most with Delta K-s > 4 mag) variable sources discovered by the Vista Variables in the Via Lactea (VVV) survey. Based on the spectral features, 25 sources are classified as eruptive young stellar objects (YSOs), including 15 newly identified FUors, six with long-lasting, but EXor-like bursts of magnetospheric accretion and four displaying outflow-dominated spectra. By examining the photometric behaviours of eruptive YSOs, we found most FUor-type outbursts have higher amplitudes (Delta K-s and Delta W2), faster eruptive time-scales and bluer infrared colours than the other outburst types. In addition, we identified seven post-MS variables apparently associated with deep dipping events and an eruptive star with deep aluminium monoxide absorption bands resembling those seen in the V838 Mon stellar merger.
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    Stellar atmospheric parameters and chemical abundances of ∼5 million stars from S-PLUS multiband photometry
    (EDP SCIENCES S A, 2025) Ferreira Lopes, C. E.; Gutierrez-Soto, L. A.; S. Ferreira Alberice, V.; Monsalves, N.; Hazarika, D.; Catelan, Márcio; Placco, V. M.; Limberg, G.; Almeida-Fernandes, F.; Perottoni, H. D.; Smith Castelli, A. V.; Akras, S.; Alonso-Garcia, J.; Cordeiro, V.; Jaque Arancibia, M.; Daflon, S.; Dias, B.; Goncalves, D. R.; Machado-Pereira, E.; Lopes, A. R.; Bom, C. R.; Thom de Souza, R. C.; de Isidio, N. G.; Alvarez-Candal, A.; De Rossi, M. E.; Bonatto, C. J.; Cubillos Palma, B.; Borges Fernandes, M.; Humire, P. K.; Oliveira Schwarz, G. B.; Schoenell, W.; Kanaan, A.; Mendes de Oliveira, C.
    Context. The APOGEE, GALAH, and LAMOST spectroscopic surveys have substantially contributed to our understanding of the Milky Way by providing a wide range of stellar parameters and chemical abundances. Complementing these efforts, photometric surveys that include narrowband and medium-band filters, such as Southern Photometric Local Universe Survey (S-PLUS), provide a unique opportunity to estimate the atmospheric parameters and elemental abundances for a much larger number of sources, compared to spectroscopic surveys., Aims. Our aim is to establish methodologies for extracting stellar atmospheric parameters and selected chemical abundances from S-PLUS photometric data, which cover approximately 3000 square degrees, by applying seven narrowband and five broadband filters., Methods. We used all 66 S-PLUS colors to estimate parameters based on three different training samples from the LAMOST, APOGEE, and GALAH surveys, applying cost-sensitive neural network (NN) and random forest (RF) algorithms. We kept the stellar abundances that lacked corresponding absorption features in the S-PLUS filters to test for spurious correlations in our method. Furthermore, we evaluated the effectiveness of the NN and RF algorithms by using estimated T-eff and log g values as the input features to determine other stellar parameters and abundances. The NN approach consistently outperforms the RF technique on all parameters tested. Moreover, incorporating T-eff and log g leads to an improvement in the estimation accuracy by approximately 3%. We kept only parameters with a goodness-of-fit higher than 50%., Results. Our methodology allowed us to obtain reliable estimates for fundamental stellar parameters (T-eff, log g, and [Fe/H]) and elemental abundance ratios such as [alpha/Fe], [Al/Fe], [C/Fe], [Li/Fe], and [Mg/Fe] for approximately five million stars across the Milky Way, with a goodness-of-fit above 60%. We also obtained additional abundance ratios, including [Cu/Fe], [O/Fe], and [Si/Fe]. However, these ratios should be used cautiously due to their low accuracy or lack of a clear relationship with the S-PLUS filters. Validation of our estimations and methods was performed using star clusters, Transiting Exoplanet Survey Satellite (TESS) data and Javalambre Photometric Local Universe Survey (J-PLUS) photometry, further demonstrating the robustness and accuracy of our approach., Conclusions. By leveraging S-PLUS photometric data and advanced machine learning techniques, we have established a robust framework for extracting fundamental stellar parameters and chemical abundances from medium-band and narrowband photometric observations. This approach offers a cost-effective alternative to high-resolution spectroscopy. The estimated parameters hold significant potential for future studies, particularly when classifying objects within our Milky Way or gaining insights into its various stellar populations.
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    Stellar density profile and mass of the Milky Way bulge from VVV data
    (2016) Valenti, E.; Zoccali, M.; Gonzalez, O. A.; Minniti, D.; Alonso-Garcia, J.; Marchetti, E.; Hempel, M.; Renzini, A.; Rejkuba, M.
    We present the first stellar density profile of the Milky Way bulge that reaches latitude b = 0 degrees. The profile was derived by counting red clump stars within the colour-magnitude diagram that was constructed using the new PSF-fitting photometry from VISTA Variables in the Via Lactea (VVV) survey data. The new stellar density map covers the area between vertical bar l vertical bar <= 10 degrees and vertical bar b vertical bar <= 45 degrees with unprecedented accuracy, allowing the stellar kinematics from the Giraffe Inner Bulge Spectroscopic Survey (GIBS) to be linked to the stellar mass density distribution. In particular, the location of the central velocity-dispersion peak from GIBS matches a high over-density in the VVV star count map. By scaling the total luminosity function (LF) obtained from all VVV fields to the LF from Zoccali et al.(2003), we obtain the first fully empirical estimate of the mass in stars and in remnants of the Galactic bulge. Within (vertical bar b vertical bar < 9.5 degrees, vertical bar l vertical bar < 10 degrees), the Milky Way bulge stellar mass is 2.0 +/- 0.3 x 10(10) M-circle dot..
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    The VISTA Variables in the Via Lactea extended (VVVX) ESO public survey: Completion of the observations and legacy
    (2024) Saito, R. K.; Hempel, M.; Alonso-Garcia, J.; Lucas, P. W.; Minniti, D.; Alonso, S.; Baravalle, L.; Borissova, J.; Caceres, C.; Chene, A. N.; Cross, N. J. G.; Duplancic, F.; Garro, E. R.; Gomez, M.; Ivanov, V. D.; Kurtev, R.; Luna, A.; Majaess, D.; Navarro, M. G.; Pullen, J. B.; Rejkuba, M.; Sanders, J. L.; Smith, L. C.; Albino, P. H. C.; Alonso, M. V.; Amores, E. B.; Angeloni, R.; Arias, J. I.; Arnaboldi, M.; Barbuy, B.; Bayo, A.; Beamin, J. C.; Bedin, L. R.; Bellini, A.; Benjamin, R. A.; Bica, E.; Bonatto, C. J.; Botan, E.; Braga, V. F.; Brown, D. A.; Cabral, J. B.; Camargo, D.; Garatti, Caratti O. A.; Carballo-Bello, J. A.; Catelan, M.; Chavero, C.; Chijani, M. A.; Claria, J. J.; Coldwell, G. V.; Pena, C. Contreras; Contreras Ramos, R.; Corral-Santana, J. M.; Cortes, C. C.; Cortes-Contreras, M.; Cruz, P.; Daza-Perilla, I. V.; Debattista, V. P.; Dias, B.; Donoso, L.; D'Souza, R.; Emerson, J. P.; Federle, S.; Fermiano, V.; Fernandez, J.; Fernandez-Trincado, J. G.; Ferreira, T.; Ferreira Lopes, C. E.; Firpo, V.; Flores-Quintana, C.; Fraga, L.; Froebrich, D.; Galdeano, D.; Gavignaud, I.; Geisler, D.; Gerhard, O. E.; Gieren, W.; Gonzalez, O. A.; Gramajo, L. V.; Gran, F.; Granitto, P. M.; Griggio, M.; Guo, Z.; Gurovich, S.; Hilker, M.; Jones, H. R. A.; Kammers, R.; Kuhn, M. A.; Kumar, M. S. N.; Kundu, R.; Lares, M.; Libralato, M.; Lima, E.; Maccarone, T. J.; Marchant Cortes, P.; Martin, E. L.; Masetti, N.; Matsunaga, N.; Mauro, F.; McDonald, I.; Mejias, A.; Mesa, V.; Milla-Castro, F. P.; Minniti, J. H.; Moni Bidin, C.; Montenegro, K.; Morris, C.; Motta, V.; Navarete, F.; Navarro Molina, C.; Nikzat, F.; Nilo Castellon, J. L.; Obasi, C.; Ortigoza-Urdaneta, M.; Palma, T.; Parisi, C.; Pena Ramirez, K.; Pereyra, L.; Perez, N.; Petralia, I.; Pichel, A.; Pignata, G.; Ramirez Alegria, S.; Rojas, A. F.; Rojas, D.; Roman-Lopes, A.; Rovero, A. C.; Saroon, S.; Schmidt, E. O.; Schroeder, A. C.; Schultheis, M.; Sgro, M. A.; Solano, E.; Soto, M.; Stecklum, B.; Steeghs, D.; Tamura, M.; Tissera, P.; Valcarce, A. A. R.; Valotto, C. A.; Vasquez, S.; Villalon, C.; Villanova, S.; Vivanco Cadiz, F.; Zelada Bacigalupo, R.; Zijlstra, A.; Zoccali, M.
    Context. The ESO public survey VISTA Variables in the Via Lactea (VVV) surveyed the inner Galactic bulge and the adjacent southern Galactic disk from 2009-2015. Upon its conclusion, the complementary VVV extended (VVVX) survey has expanded both the temporal as well as spatial coverage of the original VVV area, widening it from 562 to 1700 sq. deg., as well as providing additional epochs in JHKs filters from 2016-2023.
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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.