المؤلفون: Navarrete, Camila, Catelan, Márcio, Ramos, Rodrigo Contreras, Alonso-García, Javier, Gran, Felipe, Dékány, István, Minniti, Dante

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Astrophysics of Galaxies

الوصف: $\omega$ 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 $\omega$ Cen, using the VISTA telescope. We assembled an unprecedented homogeneous and complete $J$ and $K_{\rm S}$ near-IR catalog of variable stars in the field of $\omega$ 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.
Comment: Conference Proceedings. Wide-field variability surveys: a 21st-century perspective. 6 pages, 4 figures, in press

الوصول الحر: http://arxiv.org/abs/1706.03899Test

المؤلفون: 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 J., 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, Manuela

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics

الوصف: We use deep multi-epoch near-IR images of the VISTA Variables in the V\'ia L\'actea (VVV) Survey to search for RR Lyrae stars towards 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 $>100$ sigma detection for this candidate globular cluster, that is centered at equatorial coordinates $RA_{J2000}=$16:10:30.0, $DEC_{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 $K_s=13.35 \pm 0.05$, and $J-K_s=1.30 \pm 0.05$. We present the cluster RR Lyrae positions, magnitudes, colors, periods and amplitudes. The presence of RR Lyrae indicates an old globular cluster, with 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, $=0.540$ days, and argue that this is a relatively metal-poor cluster with $[Fe/H] = -1.5 \pm 0.4$ dex. The mean extinction and reddening for this cluster are $A_{K_s}=0.38 \pm 0.02$, and $E(J-K_s)=0.72 \pm 0.02$ 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 $(m-M)_0 = 14.38 \pm 0.03$ mag, implying a distance $D = 7.5 \pm 0.2$ kpc, and a Galactocentric distance $R_G=4.3$ kpc.
Comment: 7 pages, 4 figures. ApJL, in press

الوصول الحر: http://arxiv.org/abs/1703.02033Test

المؤلفون: Minniti, Dante, Dékány, Istvan, Majaess, Daniel, Palma, Tali, Pullen, Joyce, Rejkuba, Marina, Alonso-García, Javier, Catelan, Marcio, Ramos, Rodrigo Contreras, Gonzalez, Oscar A., Hempel, Maren, Irwin, Mike, Lucas, Philip W., Saito, Roberto K., Tissera, Patricia, Valenti, Elena, Zoccali, Manuela

مصطلحات موضوعية: Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics

الوصف: Deep near-IR images from the VISTA Variables in the V\'ia L\'actea (VVV) Survey were used to search for RR Lyrae stars in the Southern Galactic plane. A sizable sample of 404 RR Lyrae of type ab stars was identified across a thin slice of the 4$^{\rm th}$ Galactic quadrant ($295\deg < l < 350\deg$, $-2.24\deg < b < -1.05\deg$). The sample's distance distribution exhibits a maximum density that occurs at the bulge tangent point, which implies that this primarily Oosterhoff type I population of RRab stars does not trace the bar delineated by their red clump counterparts. The bulge RR Lyrae population does not extend beyond $l \sim340 \deg$, and the sample's spatial distribution presents evidence of density enhancements and substructure that warrants further investigation. Indeed, the sample may be employed to evaluate Galactic evolution models, and is particularly lucrative since half of the discovered RR Lyrae are within reach of Gaia astrometric observations.
Comment: 10 pages, 13 figures. AJ, in press

الوصول الحر: http://arxiv.org/abs/1703.01711Test

المؤلفون: Elorrieta, Felipe, Eyheramendy, Susana, Jordán, Andrés, Dékány, István, Catelan, Márcio, Angeloni, Rodolfo, Alonso-García, Javier, Contreras-Ramos, Rodrigo, Gran, Felipe, Hajdu, Gergely, Espinoza, Néstor, Saito, Roberto K., Minniti, Dante

مصطلحات موضوعية: Astrophysics - Instrumentation and Methods for Astrophysics

الوصف: Variable stars of RR Lyrae type are a prime tool to obtain distances to old stellar populations in the Milky Way, and one of the main aims of the Vista Variables in the Via Lactea (VVV) near-infrared survey is to use them to map the structure of the Galactic Bulge. Due to the large number of expected sources, this requires an automated mechanism for selecting RR Lyrae,and particularly those of the more easily recognized type ab (i.e., fundamental-mode pulsators), from the 10^6-10^7 variables expected in the VVV survey area. In this work we describe a supervised machine-learned classifier constructed for assigning a score to a K_s-band VVV light curve that indicates its likelihood of being ab-type RR Lyrae. We describe the key steps in the construction of the classifier, which were the choice of features, training set, selection of aperture and family of classifiers. We find that the AdaBoost family of classifiers give consistently the best performance for our problem, and obtain a classifier based on the AdaBoost algorithm that achieves a harmonic mean between false positives and false negatives of ~7% for typical VVV light curve sets. This performance is estimated using cross-validation and through the comparison to two independent datasets that were classified by human experts.
Comment: 11 pages, 7 figures. Astronomy & Astrophysics, in press

الوصول الحر: http://arxiv.org/abs/1610.05707Test

المؤلفون: Valcarce, Aldo A. R., Catelan, Márcio, Alonso-García, Javier, Contreras Ramos, Rodrigo, Alves, Sanzia

الوصف: The distribution of horizontal branch stars in globular cluster color-magnitude diagrams is a sensitive probe of their original helium abundances. In this sense, they have been extensively used recently as indicators of possible variations in the helium content Y among the different populations of stars within individual globular clusters. However, recent analyses based on visual and near-ultraviolet color-magnitude diagrams have provided conflicting results. In order to clarify the situation, in this presentation we discuss the optimum ranges of applicability of this “HB Y test” in different filter systems, in terms of the temperature range covered by the horizontal branch stars. In particular, we discuss the case of M3 (NGC 5272), based on multi-band photometry (HST, Strömgren, Johnson), thus setting new and tight constraints on the internal range in Y within this cluster. We also provide an application of this "HB Y test" to other selected clusters.

العلاقة: https://repositorio.uc.cl/handle/11534/81407Test

الإتاحة: https://repositorio.uc.cl/handle/11534/81407Test

المؤلفون: Navarrete, Camila, Catelan, Marcio, Contreras Ramos, Rodrigo, Alonso-García, Javier, Gran, Felipe, Dékány, István, Minniti, Dante

الوصف: 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.

العلاقة: https://doi.org/10.1051/epjconf/201715207005Test; https://repositorio.uc.cl/handle/11534/81206Test

الإتاحة: https://doi.org/10.1051/epjconf/201715207005Test
https://repositorio.uc.cl/handle/11534/81206Test

المؤلفون: Palma, Tali, Minniti, Dante, Dékány, Istvan, Clariá, Juan J., Alonso-García, Javier, Gramajo, Luciana V., Alegría, Sebastian Ramírez, Bonatto, Charles

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Astrophysics of Galaxies

الوصف: This project is a massive near-infrared (NIR) search for variable stars in highly reddened and obscured open cluster (OC) fields projected on regions of the Galactic bulge and disk. The search is performed using photometric NIR data in the $J$-, $H$- and $K_s$- bands obtained from the Vista Variables in the V\'ia L\'actea (VVV) Survey. We performed in each cluster field a variability search using Stetson's variability statistics to select the variable candidates. Later, those candidates were subjected to a frequency analysis using the Generalized Lomb-Scargle and the Phase Dispersion Minimization algorithms. The number of independent observations range between 63 and 73. The newly discovered variables in this study, 157 in total in three different known OCs, are classified based on their light curve shapes, periods, amplitudes and their location in the corresponding color-magnitude $(J-K_s,K_s)$ and color-color $(H-K_s,J-H)$ diagrams. We found 5 possible Cepheid stars which, based on the period-luminosity relation, are very likely type II Cepheids located behind the bulge. Among the newly discovered variables, there are eclipsing binaries, $\delta$ Scuti, as well as background RR Lyrae stars. Using the new version of the Wilson & Devinney code as well as the "Physics Of Eclipsing Binaries" (PHOEBE) code, we analyzed some of the best eclipsing binaries we discovered. Our results show that these studied systems turn out to be ranging from detached to double-contact binaries, with low eccentricities and high inclinations of approximately $80^{\circ}$. Their surface temperatures range between $3500$K and $8000$K.
Comment: 34 pages, 10 figures, 7 tables. Accepted for publication in New Astronomy

الوصول الحر: http://arxiv.org/abs/1606.05028Test

المؤلفون: Nataf, David M., Gonzalez, Oscar A., Casagrande, Luca, Zasowski, Gail, Wegg, Christopher, Wolf, Christian, Kunder, Andrea, Alonso-Garcia, Javier, Minniti, Dante, Rejkuba, Marina, Saito, Roberto K., Valenti, Elena, Zoccali, Manuela, Poleski, Radoslaw, Pietrzynski, Grzegorz, Skowron, Jan, Soszynski, Igor, Szymanski, Michal K., Udalski, Andrzej, Ulaczyk, Krzystof, Wyrzykowski, Lukasz

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies

الوصف: We investigate interstellar extinction curve variations toward $\sim$4 deg$^{2}$ of the inner Milky Way in $VIJK_{s}$ photometry from the OGLE-III and $VVV$ surveys, with supporting evidence from diffuse interstellar bands and $F435W,F625W$ photometry. We obtain independent measurements toward $\sim$2,000 sightlines of $A_{I}$, $E(V-I)$, $E(I-J)$, and $E(J-K_{s})$, with median precision and accuracy of 2%. We find that the variations in the extinction ratios $A_{I}/E(V-I)$, $E(I-J)/E(V-I)$ and $E(J-K_{s})/E(V-I)$ are large (exceeding 20%), significant, and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how $R_{V}$ is varied. Furthermore, we demonstrate that variations in the shape of the extinction curve has at least two degrees of freedom, and not one (e.g. $R_{V}$), which we conform with a principal component analysis. We derive a median value of $=13.44$, which is $\sim$60% higher than the "standard" value. We show that the Wesenheit magnitude $W_{I}=I-1.61(I-J)$ is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that $R_{V}$ variations correctly capture variations in the extinction curve, we argue that systematic errors in the distance ladder from studies of type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by $\sim$100%, and lack sensitivity to extinction curve variations.
Comment: 16 pages, 13 figures, 3 tables, accepted to MNRAS, small revisions due to editor's comments and suggestions from the international astronomical community

الوصول الحر: http://arxiv.org/abs/1510.01321Test

المؤلفون: Cohen, Roger E., Hempel, Maren, Mauro, Francesco, Geisler, Douglas, Alonso-Garcia, Javier, Kinemuchi, Karen

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Astrophysics of Galaxies

الوصف: We present wide field near-infrared photometry of 12 Galactic globular clusters, typically extending from the tip of the cluster red giant branch (RGB) to the main sequence turnoff. Using recent homogenous values of cluster distance, reddening and metallicity, the resulting photometry is directly compared to the predictions of several recent libraries of stellar evolutionary models. Of the sets of models investigated, Dartmouth and Victoria-Regina models best reproduce the observed RGB morphology, albeit with offsets in J-Ks color which vary in their significance in light of all sources of observational uncertainty. Therefore, we also present newly recalibrated relations between near-IR photometric indices describing the upper RGB versus cluster iron abundance as well as global metallicity. The influence of enhancements in alpha elements and helium are analyzed, finding that the former affect the morphology of the upper RGB in accord with model predictions. Meanwhile, the empirical relations we derive are in good agreement with previous results, and minor discrepancies can likely be attributed to differences in the assumed cluster distances and reddenings. In addition, we present measurements of the horizontal branch (HB) and RGB bump magnitudes, finding a non-negligible dependence of the near-IR HB magnitude on cluster metallicity. Lastly, we discuss the influence of assumed cluster distances, reddenings and metallicities on our results, finding that our empirical relations are generally insensitive to these factors to within their uncertainties.
Comment: AJ, in press. Replaced Fig. 8, figure quality in this version reduced due to size limits in some cases

الوصول الحر: http://arxiv.org/abs/1509.01470Test

المؤلفون: Blanton, Michael R, Bershady, Matthew A, Abolfathi, Bela, Albareti, Franco D, Prieto, Carlos Allende, Almeida, Andres, Alonso-García, Javier, Anders, Friedrich, Anderson, Scott F, Andrews, Brett, Aquino-Ortíz, Erik, Aragón-Salamanca, Alfonso, Argudo-Fernández, Maria, Armengaud, Eric, Aubourg, Eric, Avila-Reese, Vladimir, Badenes, Carles, Bailey, Stephen, Barger, Kathleen A, Barrera-Ballesteros, Jorge, Bartosz, Curtis, Bates, Dominic, Baumgarten, Falk, Bautista, Julian, Beaton, Rachael, Beers, Timothy C, Belfiore, Francesco, Bender, Chad F, Berlind, Andreas A, Bernardi, Mariangela, Beutler, Florian, Bird, Jonathan C, Bizyaev, Dmitry, Blanc, Guillermo A, Blomqvist, Michael, Bolton, Adam S, Boquien, Médéric, Borissova, Jura, van den Bosch, Remco, Bovy, Jo, Brandt, William N, Brinkmann, Jonathan, Brownstein, Joel R, Bundy, Kevin, Burgasser, Adam J, Burtin, Etienne, Busca, Nicolás G, Cappellari, Michele, Carigi, Maria Leticia Delgado, Carlberg, Joleen K, Rosell, Aurelio Carnero, Carrera, Ricardo, Chanover, Nancy J, Cherinka, Brian, Cheung, Edmond, Chew, Yilen Gómez Maqueo, Chiappini, Cristina, Choi, Peter Doohyun, Chojnowski, Drew, Chuang, Chia-Hsun, Chung, Haeun, Cirolini, Rafael Fernando, Clerc, Nicolas, Cohen, Roger E, Comparat, Johan, da Costa, Luiz, Cousinou, Marie-Claude, Covey, Kevin, Crane, Jeffrey D, Croft, Rupert AC, Cruz-Gonzalez, Irene, Cuadra, Daniel Garrido, Cunha, Katia, Damke, Guillermo J, Darling, Jeremy, Davies, Roger, Dawson, Kyle, de la Macorra, Axel, Dell’Agli, Flavia, De Lee, Nathan, Delubac, Timothée, Di Mille, Francesco, Diamond-Stanic, Aleks, Cano-Díaz, Mariana, Donor, John, Downes, Juan José, Drory, Niv, du Mas des Bourboux, Hélion, Duckworth, Christopher J, Dwelly, Tom, Dyer, Jamie, Ebelke, Garrett, Eigenbrot, Arthur D, Eisenstein, Daniel J, Emsellem, Eric, Eracleous, Mike, Escoffier, Stephanie, Evans, Michael L, Fan, Xiaohui, Fernández-Alvar, Emma

المصدر: The Astronomical Journal. 154(1)

مصطلحات موضوعية: Space Sciences, Astronomical Sciences, Physical Sciences, cosmology: observations, galaxies: general, Galaxy: general, instrumentation: spectrographs, stars: general, surveys, astro-ph.GA, Astronomical and Space Sciences, Astronomy & Astrophysics, Astronomical sciences, Particle and high energy physics

الوصف: We describe the Sloan Digital Sky Survey IV (SDSS-IV), a project encompassing three major spectroscopic programs. The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is observing hundreds of thousands of Milky Way stars at high resolution and high signal-to-noise ratios in the near-infrared. The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is obtaining spatially resolved spectroscopy for thousands of nearby galaxies (median z ∼ 0.03). The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is mapping the galaxy, quasar, and neutral gas distributions between z ~ 0.6 and 3.5 to constrain cosmology using baryon acoustic oscillations, redshift space distortions, and the shape of the power spectrum. Within eBOSS, we are conducting two major subprograms: the SPectroscopic IDentification of eROSITA Sources (SPIDERS), investigating X-ray AGNs and galaxies in X-ray clusters, and the Time Domain Spectroscopic Survey (TDSS), obtaining spectra of variable sources. All programs use the 2.5 m Sloan Foundation Telescope at the Apache Point Observatory; observations there began in Summer 2014. APOGEE-2 also operates a second near-infrared spectrograph at the 2.5 m du Pont Telescope at Las Campanas Observatory, with observations beginning in early 2017. Observations at both facilities are scheduled to continue through 2020. In keeping with previous SDSS policy, SDSS-IV provides regularly scheduled public data releases; the first one, Data Release 13, was made available in 2016 July.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/0v44n629Test
https://escholarship.org/content/qt0v44n629/qt0v44n629.pdfTest