170,421 research outputs found
Further probing the nature of FSR 1767
No full textWith Two-Micron All-Sky Survey (2MASS) photometry and proper motions, Bonatto et al. suggested that FSR 1767 is a globular cluster (GC), while with J and K NTT/SOFI photometry Froebrich, Meusinger & Scholz concluded that it is not a star cluster. In this study, we combine previous and new evidence that are consistent with a GC. For instance, we show that the horizontal branch (HB) and red giant branch (RGB) stars, besides sharing a common proper motion, have radial density profiles that consistently follow the King`s law independently. Reddening maps around FSR 1767 are built using the bulge RGB as reference and also Schlegel`s extinction values to study local absorptions. Both approaches provide similar maps and show that FSR 1767 is not located in a dust window, which otherwise might have produced the stellar overdensity. Besides, neighbouring regions of similar reddening as FSR 1767 do not present the blue HB stars that are a conspicuous feature in the colour-magnitude diagram of FSR 1767. We report the presence of a compact group of stars located in the central parts of FSR 1767. It appears to be a detached post-collapse core, similar to those of other nearby low-luminosity GCs projected towards the bulge. We note that while the NTT/SOFI photometry of the star cluster FSR 1716 matches perfectly that from 2MASS, it shows a considerable offset for FSR 1767. We discuss the possible reasons why both photometries differ. We confirm our previous structural and photometric fundamental parameters for FSR 1767, which are consistent with a GC.CNPqFAPESP (Brazil)MURST (Italy
FSR584 - a new globular cluster in the Galaxy?
No full textAims:We investigate the nature of the recently catalogued star cluster candidate FSR 584, which is projected in the direction of the molecular cloud W 3 and may be the nearest globular cluster to the Sun.
Methods: 2MASS colour-magnitude diagrams, the stellar radial density profile, and proper motions are employed to derive fundamental and structural parameters.
Results: The colour-magnitude diagram morphology and the radial density profile show that FSR 584 is an old star cluster. With proper motions, the properties of FSR 584 are consistent with a metal-poor ([Fe/H]≈-2) globular cluster with a well-defined turnoff and evidence of a blue horizontal-branch. FSR 584 might be a Palomar-like halo globular cluster that is moving towards the Galactic plane, currently at ≈20 pc above it. The distance from the Sun is d_sun≈1.4 kpc, and it is located at ≈1 kpc outside the Solar circle. The radial density profile is characterized by a core radius of R_core=0.3±0.1 pc. However, we cannot exclude the possibility of an old open cluster.
Conclusions: Near-infrared photometry coupled to proper motions support the scenario where FSR 584 is a new globular cluster in the Galaxy. The absorption is A_V=9.2±0.6, which makes it a limiting object in the optical and explains why it has so far been overlooked
Globular cluster system and Milky Way properties revisited
No full textAims.Updated data of the 153 Galactic globular clusters are used to readdress fundamental parameters of the Milky Way, such as the distance of the Sun to the Galactic centre, the bulge and halo structural parameters, and cluster destruction rates.
Methods: .We build a reduced sample that has been decontaminated of all the clusters younger than 10 Gyr and of those with retrograde orbits and/or evidence of relation to dwarf galaxies. The reduced sample contains 116 globular clusters that are tested for whether they were formed in the primordial collapse.
Results: .The 33 metal-rich globular clusters ([Fe/H]≥-0.75) of the reduced sample basically extend to the Solar circle and are distributed over a region with the projected axial-ratios typical of an oblate spheroidal, Δ x:Δ y:Δ z≈1.0:0.9:0.4. Those outside this region appear to be related to accretion. The 81 metal-poor globular clusters span a nearly spherical region of axial-ratios ≈1.0:1.0:0.8 extending from the central parts to the outer halo, although several clusters in the external region still require detailed studies to unravel their origin as accretion or collapse. A new estimate of the Sun's distance to the Galactic centre, based on the symmetries of the spatial distribution of 116 globular clusters, is provided with a considerably smaller uncertainty than in previous determinations using globular clusters, R_O=7.2±0.3 kpc. The metal-rich and metal-poor radial-density distributions flatten for R_GC≤2 kpc and are represented well over the full Galactocentric distance range both by a power-law with a core-like term and Sérsic's law; at large distances they fall off as ̃ R-3.9.
Conclusions: .Both metallicity components appear to have a common origin that is different from that of the dark matter halo. Structural similarities between the metal-rich and metal-poor radial distributions and the stellar halo are consistent with a scenario where part of the reduced sample was formed in the primordial collapse and part was accreted in an early period of merging. This applies to the bulge as well, suggesting an early merger affecting the central parts of the Galaxy. The present decontamination procedure is not sensitive to all accretions (especially prograde) during the first Gyr, since the observed radial density profiles still preserve traces of the earliest merger(s). We estimate that the present globular cluster population corresponds to ≤23±6% of the original one. The fact that the volume-density radial distributions of the metal-rich and metal-poor globular clusters of the reduced sample follow both a core-like power-law, and Sérsic's law indicates that we are dealing with spheroidal subsystems at all scales
Ca(BH4)2 + MgH2: Desorption Reaction and Role of Mg on Its Reversibility
No full textThe Ca(BH4)2–MgH2 composite system represents a promising candidate for mobile hydrogen storage due to a 10.5 wt % theoretical hydrogen storage capacity and an estimated equilibrium temperature lower than 160 °C. For this system, the reversibility was achieved without further addition of additives. In this study, the decomposition path of the Ca(BH4)2 + MgH2 composite system is investigated in detail by in situ synchrotron radiation powder X-ray diffraction and differential scanning calorimetry combined with thermogravimetry. The sorption properties are analyzed by volumetric measurements. 11B{1H} solid state magic angle spinning–nuclear magnetic resonance was employed for the characterization of the final amorphous or nanocrystalline boron-based decomposition products. This study shows that the intermediate formation of Ca4Mg3H14 upon dehydrogenation of the Ca(BH4)2–MgH2 composite system is not a necessary step, and its presence can be adjusted modifying the preparation procedure. Moreover, the d-value mismatch calculated for the {111}CaB6/{1011}Mg plane pair is the lowest among the other plane pairs considered in the system. The mismatch in the third direction between CaB6 and Mg is also extremely good. These findings propose Mg as a supporter of the heterogeneous nucleation of CaB6 during decomposition of the Ca(BH4)2 + MgH2 composite system
Sorption properties and reversibility of Ti(IV) and Nb(V)-fluoride doped-Ca(BH4)(2)-MgH2 system
No full textIn the last decade, alkaline and alkaline earth metal tetrahydroborates have been the focuses of the research due to their high gravimetric and volumetric hydrogen densities. Among them, Ca(BH4)(2) and the Ca(BH4)(2) + MgH2 reactive hydride composites (RHC), were calculated to have the ideal thermodynamic properties which fall within the optimal range for mobile applications. In this study, the addition of NbF5 or TiF4 to the Ca(BH4)(2) + MgH2 reactive hydride composite system was attempted aiming to obtain a full reversible system with the simultaneous suppression of CaB12H12. Structural characterization of the specimens was performed by means of in-situ Synchrotron Radiation Powder X-ray diffraction (SR-PXD) and B-11{H-1} Solid State Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR). The evolution of the chemical state of the Nb- and Ti-based additives was monitored by X-ray Absorption Near Edge Structure (XANES). The addition of NbF5 or TiF4 to the Ca(BH4)(2) + MgH2 system have not suppressed completely the formation of CaB12H12 and only a slight improvement concerning the reversible reaction was displayed just in the case of Nb-doped composite material. (C) 2014 Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
FSR 1767 - a new globular cluster in the Galaxy
No full textThe globular cluster (GC) nature of the recently catalogued candidate FSR1767 is established in the present work. It turns out to be the closest GC so far detected in the Galaxy. The nature of this object is investigated by means of 2MASS colour-magnitude diagrams (CMDs), the stellar radial density profile (RDP) and proper motions (PM). The properties are consistent with an intermediate-metallicity ([Fe/H] ~ -1.2) GC with a well-defined turnoff (TO), red giant branch (RGB) and blue horizontal branch (HB). The distance of FSR1767 from the Sun is dsolar ~ 1.5kpc, and it is located at the Galactocentric distance RGC ~ 5.7kpc. With the space velocity components (V, W) = (184 +/- 14, -43 +/- 14)kms-1, FSR1767 appears to be a Palomar-like GC with MV ~ -4.7, which currently lies ~57pc below the Galactic plane. The RDP is well represented by a King profile with the core and tidal radii Rcore = 0.24 +/- 0.08pc and Rtidal = 3.1 +/- 1.0pc, respectively, with a small half-light radius Rh = 0.60 +/- 0.15pc. The optical absorption is moderate for an infrared GC, AV = 6.2 +/- 0.3, which together with its central direction and enhanced contamination explains why it has so far been overlooked
Espacio, memoria y género : Españolas y argentinas en contextos de guerra, dictaduras y exilios
No full textEn este contexto de bienvenida efervescencia feminista, resulta fundamental insistir en la importancia de la construcción de una memoria histórica que permita anclar sentidos en una perspectiva temporal más amplia que la de la actualidad. Es de celebrar entonces la aparición de este volumen, que se encomienda la indispensable tarea de enriquecer el presente a partir de la relectura del pasado, no solo a través del análisis de testimonios sino también de ficciones. En su conjunto, la obra contiene importantes contribuciones para diversos campos disciplinares, debido a que en sus hallazgos se cruzan los estudios de género y feministas, los estudios de la memoria colectiva y los estudios literarios transatlánticos y comparativos. En forma no menos apreciable, contribuye a paliar esa falta de conocimiento histórico que puede conducir a lecturas anacrónicas del presente, y resulta un estímulo para el largo camino que aún queda por recorrer, ya que brinda herramientas para visibilizar que determinados olvidos no han sido casuales.Tabla de contenidos: Introducción / Mariela Sánchez y Virginia Bonatto. Una voz desde el exilio: Mercè Rodoreda (1908-1983) / Gladys Granata de Egües. Narrativas de filiación en búsqueda de la tradición perdida. La correspondencia Rosa Chacel / Ana María Moix / Silvia Cárcamo. "Solo queda contar": Lugares de memoria, destierro y secuelas de la Guerra Civil y el franquismo en las novelas Estuvimos cantando de María García Campelo, Ultimas miradas antes de partir de Milagros Díaz Martínez y Solo queda saltar de María Rosa Lojo / Mariela Sánchez. Espacio y memoria. Las mujeres en los relatos concentracionarios del exilio español en Africa del Norte / Mercedes Giuffré. "Esto no es Londres, cielo. Aquí las mujeres se quedan en casa": la mirada femenina de la guerra y la posguerra españolas en La buena letra, de Rafael Chirbes / Daniela C. Serber. Figuras de milicianas en cuatro relatos de mujeres: Contra viento y marea y Memoria de la melancolía de María Teresa León, Mi guerra de España de Mika Etchebéhère y Así fue pasando el tiempo de María de la Luz Mejías Correa / Virginia Bonatto. El silencio y la memoria femeninos en Cautivas de Gabriela Saidón y en Hija del silencio de Manuela Fingueret / Elsa Beatriz Grillo, Laura Noemí Conci y Lucía Isabel Muñoz. Reversiones y desplazamientos de la cautiva: la presa política como la "nueva cautiva" argentina / Lucila Rosario Lastero. Colofón. Maestras de la República. Derroteros del exilio: Argentina / Raquel Macciuci.
Espacio, memoria y género : Españolas y argentinas en contextos de guerra, dictaduras y exilios
No full textEn este contexto de bienvenida efervescencia feminista, resulta fundamental insistir en la importancia de la construcción de una memoria histórica que permita anclar sentidos en una perspectiva temporal más amplia que la de la actualidad. Es de celebrar entonces la aparición de este volumen, que se encomienda la indispensable tarea de enriquecer el presente a partir de la relectura del pasado, no solo a través del análisis de testimonios sino también de ficciones. En su conjunto, la obra contiene importantes contribuciones para diversos campos disciplinares, debido a que en sus hallazgos se cruzan los estudios de género y feministas, los estudios de la memoria colectiva y los estudios literarios transatlánticos y comparativos. En forma no menos apreciable, contribuye a paliar esa falta de conocimiento histórico que puede conducir a lecturas anacrónicas del presente, y resulta un estímulo para el largo camino que aún queda por recorrer, ya que brinda herramientas para visibilizar que determinados olvidos no han sido casuales.Tabla de contenidos: Introducción / Mariela Sánchez y Virginia Bonatto. Una voz desde el exilio: Mercè Rodoreda (1908-1983) / Gladys Granata de Egües. Narrativas de filiación en búsqueda de la tradición perdida. La correspondencia Rosa Chacel / Ana María Moix / Silvia Cárcamo. "Solo queda contar": Lugares de memoria, destierro y secuelas de la Guerra Civil y el franquismo en las novelas Estuvimos cantando de María García Campelo, Ultimas miradas antes de partir de Milagros Díaz Martínez y Solo queda saltar de María Rosa Lojo / Mariela Sánchez. Espacio y memoria. Las mujeres en los relatos concentracionarios del exilio español en Africa del Norte / Mercedes Giuffré. "Esto no es Londres, cielo. Aquí las mujeres se quedan en casa": la mirada femenina de la guerra y la posguerra españolas en La buena letra, de Rafael Chirbes / Daniela C. Serber. Figuras de milicianas en cuatro relatos de mujeres: Contra viento y marea y Memoria de la melancolía de María Teresa León, Mi guerra de España de Mika Etchebéhère y Así fue pasando el tiempo de María de la Luz Mejías Correa / Virginia Bonatto. El silencio y la memoria femeninos en Cautivas de Gabriela Saidón y en Hija del silencio de Manuela Fingueret / Elsa Beatriz Grillo, Laura Noemí Conci y Lucía Isabel Muñoz. Reversiones y desplazamientos de la cautiva: la presa política como la "nueva cautiva" argentina / Lucila Rosario Lastero. Colofón. Maestras de la República. Derroteros del exilio: Argentina / Raquel Macciuci.
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