7,502 research outputs found

    The Red Giant Branch in Near-Infrared Colour-Magnitude Diagrams. II: The luminosity of the Bump and the Tip

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    We present new empirical calibrations of the Red Giant Branch (RGB) Bump and Tip based on a homogeneous near-Infrared database of 24 Galactic Globular Clusters. The luminosities of the RGB Bump and Tip in the J, H and K bands and their dependence on the cluster metallicity have been studied, yielding empirical relationships. By using recent transformations between the observational and theoretical planes, we also derived similar calibrations in terms of bolometric luminosity. Direct comparison between updated theoretical models and observations show an excellent agreement. The empirical calibration of the RGB Tip luminosity in the near-Infrared passbands presented here is a fundamental tool to derive distances to far galaxies beyond the Local Group, in view of using the new ground-based adaptive optics facilities and, in the next future, the James Webb Space Telescope.Comment: 7 pages, 7 figures, accepted for publication in MNRA

    Assessment of fruit and vegetable residues suitable for renewable energy production: GIS-based model for developing new frontiers within the context of circular economy

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    Due to the necessity of developing renewable energy sources, the anaerobic digestion for producing biomethane has developed significantly in the last years, since it allows to both reduce disposal treatment and produce green energy. In this field, fruit and vegetable wastes have been recently put forward, since they could represent a suitable resource for producing biomethane as a new frontier within the context of a circular economy. This study aims at filling the gap in the knowledge of the production, quantities and biogas potential production of these residues. On this basis, a GIS-based model was developed and applied to the Sicily region by investigating the specific regulatory framework as well as by analysing descriptive statistics. The results of the GIS analyses enabled the localisation of the highest productive territorial areas and highlighted where fruit and vegetable wastes are abundantly located. In this regard, about 7 million Nm3 of biogas could be produced by reusing only the fruit and vegetable residues coming from the three most representative Sicilian wholesale markets among those considered. Finally, the regulatory framework is of crucial importance in inhibiting or supporting the use of the selected biomass in a specific sector, with regard to the case study considered

    SN/GRB connection: a statistical approach with BATSE and Asiago Catalogues

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    Recent observations suggest that some types of GRB are physically connected with SNe of type Ib/c. However, it has been pointed out by several authors that some GRBs could be associated also with other types of core-collapse SNe (type IIdw/IIn). On the basis of a comphrensive statistical study, which has made use of the BATSE and Asiago catalogues, we have found that: i) the temporal and spacial distribution of SNe-Ib/c is marginally correlated with that of the BATSE GRBs; ii) we do not confirm the existence of an association between GRBs and SNe-IIdw/IIn.Comment: Proceeding of the 4th workshop on Gamma Ray Bursts in the Afterglow Era, Rome, 2004; 4 page

    Effects of spin-phonon coupling in frustrated Heisenberg models

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    The existence and stability of spin-liquid phases represent a central topic in the field of frustrated magnetism. While a few examples of spin-liquid ground states are well established in specific models (e.g., the Kitaev model on the honeycomb lattice), recent investigations have suggested the possibility of their appearance in several Heisenberg-like models on frustrated lattices. An important related question concerns the stability of spin liquids in the presence of small perturbations in the Hamiltonian. In this respect, the magnetoelastic interaction between spins and phonons represents a relevant and physically motivated perturbation, which has been scarcely investigated so far. In this work, we study the effect of the spin-phonon coupling on prototypical models of frustrated magnetism. We adopt a variational framework based upon Gutzwiller-projected wave functions implemented with a spin-phonon Jastrow factor, providing a full quantum treatment of both spin and phonon degrees of freedom. The results on the frustrated J(1)-J(2) Heisenberg model on one- and two-dimensional (square) lattices show that, while a valence-bond crystal is prone to lattice distortions, a gapless spin liquid is stable for small spin-phonon couplings. In view of the ubiquitous presence of lattice vibrations, our results are particularly important to demonstrate the possibility that gapless spin liquids may be realized in real materials

    An empirical mass-loss law for Population II giants from the Spitzer-IRAC survey of Galactic globular clusters

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    The main aim of the present work is to derive an empirical mass-loss (ML) law for Population II stars in first and second ascent red giant branches. We used the Spitzer InfraRed Array Camera (IRAC) photometry obtained in the 3.6-8 micron range of a carefully chosen sample of 15 Galactic globular clusters spanning the entire metallicity range and sampling the vast zoology of horizontal branch (HB) morphologies. We complemented the IRAC photometry with near-infrared data to build suitable color-magnitude and color-color diagrams and identify mass-losing giant stars. We find that while the majority of stars show colors typical of cool giants, some stars show an excess of mid-infrared light that is larger than expected from their photospheric emission and that is plausibly due to dust formation in mass flowing from them. For these stars, we estimate dust and total (gas + dust) ML rates and timescales. We finally calibrate an empirical ML law for Population II red and asymptotic giant branch stars with varying metallicity. We find that at a given red giant branch luminosity only a fraction of the stars are losing mass. From this, we conclude that ML is episodic and is active only a fraction of the time, which we define as the duty cycle. The fraction of mass-losing stars increases by increasing the stellar luminosity and metallicity. The ML rate, as estimated from reasonable assumptions for the gas-to-dust ratio and expansion velocity, depends on metallicity and slowly increases with decreasing metallicity. In contrast, the duty cycle increases with increasing metallicity, with the net result that total ML increases moderately with increasing metallicity, about 0.1 Msun every dex in [Fe/H]. For Population II asymptotic giant branch stars, we estimate a total ML of <0.1 Msun, nearly constant with varying metallicity.Comment: 17 pages, 9 figures, in press on A&

    Near-Infrared photometry and spectroscopy of NGC 6539 and UKS 1: two intermediate metallicity Bulge Globular Clusters

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    Using the SofI imager at ESO/NTT and NIRSPEC spectrograph at KeckII, we have obtained J,K images and echelle spectra covering the range 1.5 - 1.8 micron for the intermediate metallicity Bulge globular clusters NGC6539 and UKS1. We find [Fe/H]=-0.76 and -0.78, respectively, and an average alpha-enhancement of +0.44 dex and +0.31 dex, consistent with previous measurements of metal rich Bulge clusters, and favoring the scenario of rapid chemical enrichment. We also measure very low 12C/13C=4.5 +/-1 isotopic ratios in both clusters, suggesting that extra-mixing mechanisms due to cool bottom processing are at work during the evolution along the Red Giant Branch. Finally, we measure accurate radial velocities of =+31 +/-4Km/s and =+57 +/-6Km/s and velocity dispersion of about 8 Km/s and 11 Km/s for NGC6539 and UKS1, respectively.Comment: 10 pages, 7 figures, accepted for publication at MNRA

    Near Infrared properties of 12 Globular Clusters toward the inner Bulge of the Galaxy

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    We present near-IR Colour-Magnitude diagrams and physical parameters for a sample of 12 galactic globular clusters located toward the inner Bulge region. For each cluster we provide measurements of the reddening, distance, photometric metallicity, luminosity of the horizontal branch red clump, and of the red giant branch bump and tip. The sample discussed here together with that presented in Valenti, Ferraro & Origlia (2007) represent the largest homogeneous catalog of Bulge globular clusters (comprising ~ 80% of the entire Bulge cluster population) ever studied. The compilation is available in electronic form on the World Wide Web (http://www.bo.astro.it/~GC/ir_archive)Comment: 2 pages, 13 figures, 4 tables, accepted for publication in MNRA

    DISCOVERY OF RR LYRAE STARS IN THE NUCLEAR BULGE OF THE MILKY WAY

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    Indexación: Web of ScienceGalactic nuclei, such as that of the Milky Way, are extreme regions with high stellar densities, and in most cases, the hosts of a supermassive black hole. One of the scenarios proposed for the formation of the Galactic nucleus is merging of primordial globular clusters. An implication of this model is that this region should host stars that are characteristically found in old Milky Way globular clusters. RR Lyrae stars are primary distance indicators, well known representatives of old and metal-poor stellar populations, and therefore are regularly found in globular clusters. Here we report the discovery of a dozen RR Lyrae type ab stars in the vicinity of the Galactic center, i.e., in the so-called nuclear stellar bulge of the Milky Way. This discovery provides the first direct observational evidence that the Galactic nuclear stellar bulge contains ancient stars (>10 Gyr old). Based on this we conclude that merging globular clusters likely contributed to the build-up of the high stellar density in the nuclear stellar bulge of the Milky Way.http://iopscience.iop.org/article/10.3847/2041-8205/830/1/L14/meta;jsessionid=2531FBFFF06C9ECBA4852FB9D1F89851.c1.iopscience.cld.iop.or

    Near-Infrared photometry of four metal-rich Bulge globular clusters: NGC6304, NGC6569, NGC6637, NGC6638

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    We present high-quality near-Infrared photometry of four Bulge metal-rich globular clusters, namely: NGC 6304, NGC 6569, NGC 6637 and NGC 6638. By using the observed Colour-Magnitude Diagrams we derived a photometric estimates of the cluster reddening and distance. We performed a detailed analysis of the Red Giant Branch, presenting a complete description of morphologic parameters and evolutionary features (Bump and Tip). Photometric estimates of the cluster metallicity have been obtained by using the updated set of relations (published by our group) linking the metal abundance to a variety of near-Infrared indices measured along the Red Giant Branch. The detection of the Red Giant Branch Bump and the Tip is also presented and briefly discussed.Comment: 12 pages, 15 figures, accepted for publication in MNRA

    Net electricity and heat generated by reusing Mediterranean agro-industrial by-products

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    The necessity to investigate suitable alternatives to conventional fossil fuels has increased interest in several renewable energy resources, especially in biomasses that are widely available and make it possible to reach environmental and socio-economic improvements. Among solutions for bioenergy production, anaerobic digestion technology allows biogas production by reusing agricultural residues and agro-industrial by-products. By considering the basic concepts of the Biogasdoneright® method, the objective of this study was to estimate the theoretical potential net electricity and heat production from anaerobic digestion of citrus pulp and olive pomace highly available worldwide. A model was developed and applied in a study area of the Mediterranean basin, where the biogas sector is still very limited despite the importance of both agricultural and agro-industrial activities, especially with regard to citrus and olive cultivation processing. Firstly, the application of a geographical information system (GIS) software tool allowed the estimation of the biogas potentially produced from citrus pulp and olive pomace re-use. Then, the development of a technical assessment demonstrated that 15.9 GWh electricity and 88,000 GJ heat per year could be generated from these by-products, satisfying approximate 17% of the electricity demand of the agricultural sector of the study area (90.2 GWh y −1 ). The achieved results could be relevant with regard to the intervention priorities established by the European Union related to the planning activities supported by the European Structural and Investment Funds within the Smart Specialisation Strategy
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