1,678 research outputs found

    The Self-Enrichment of Galactic Halo Globular Clusters: the mass-metallicity relation

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    We discuss the existence of a mass-metallicity relation among galactic halo globular clusters. The lack of any luminosity-metallicity correlation in globular cluster systems has been used as an argument against self-enrichment models of cluster formation. We show that such a relation is statistically present among the galactic Old Halo globulars. This observational correlation implies that the least massive old clusters are the most metal-rich. This is in contradiction with the idea that, if globular clusters were self-enriched systems, the most metal-rich clusters would also be the most massive ones. We further show that this anti-correlation is as predicted by self-enrichment models.Comment: 5 pages, accepted for publication in A&

    Chemical evolution of the M82 B fossil starburst

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    M82 B is an old starburst site located in the eastern part of the M82 disc. We derive the distributions of age and metallicity of the star clusters located in this region of M82 by using theoretical evolutionary population synthesis models. Our analysis is based on the comparison of the BVIJBVIJ photometry obtained by de Grijs et al. (2001) with the colours of single-generation stellar populations. We show that M82 B went through a chemical enrichment phase up to super-solar metallicities around the time of the last close encounter between M82 and its large neighbour galaxy M81. We date and confirm the event triggering the enhanced cluster formation at about 1 Gyr ago. At almost the same time an additional, distinct subpopulation of metal-poor clusters formed in the part of M82 B nearest to the galactic centre. The formation of these peculiar clusters may be related to infall of circumgalactic gas onto M82 B.Comment: 14 pages, accepted for publication in MNRA

    The effects of strong shock waves on mortality rates and percentages of pulmonary lesions in rats as a function of the number of exposures

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    The results of the study reveal that with regard to the pulmonary lesions, twice the number of exposures is compensated for by quartering the overpressure of the wave crest. With regard to the mortality rates, it reveals that halving the overpressure of the wave crest is offset by a 20-fold increase in the number of exposures

    The star cluster survivability after gas expulsion is independent of the impact of the Galactic tidal field

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    We study the impact of the tidal field on the survivability of star clusters following instantaneous gas expulsion. Our model clusters are formed with a centrally-peaked star-formation efficiency profile as a result of star-formation taking place with a constant efficiency per free-fall time. We define the impact of the tidal field as the ratio of the cluster half-mass radius to its Jacobi radius immediately after gas expulsion, λ=rh/RJ\lambda = r_{h}/R_{J}. We vary λ\lambda by varying either the Galactocentric distance, or the size (hence volume density) of star clusters. We propose a new method to measure the violent relaxation duration, in which we compare the total mass-loss rate of star clusters with their stellar evolutionary mass-loss rate. That way, we can robustly estimate the bound mass fraction of our model clusters at the end of violent relaxation. The duration of violent relaxation correlates linearly with the Jacobi radius, when considering identical clusters at different Galactocentric distances. In contrast, it is nearly constant for the solar neighbourhood clusters, slightly decreasing with λ\lambda. The violent relaxation does not last longer than 50 Myr in our simulations. Identical model clusters placed at different Galactocentric distances have the same final bound fraction, despite experiencing different impacts of the tidal field. The solar neighbourhood clusters with different densities experience only limited variations of their final bound fraction. In general, we conclude that the cluster survivability after instantaneous gas expulsion, as measured by their bound mass fraction at the end of violent relaxation, FboundF_{bound}, is independent of the impact of the tidal field, λ\lambda.Comment: accepted for publication in MNRAS, 8 pages, 5 figures,3 table

    The Old Halo metallicity gradient: the trace of a self-enrichment process

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    Based on a model of globular cluster self-enrichment published in a previous paper, we present an explanation for the metallicity gradient observed throughout the galactic Old Halo. Our self-enrichment model is based on the ability of globular cluster progenitor clouds to retain the ejecta of a first generation of Type II Supernovae. The key point is that this ability depends on the pressure exerted on the progenitor cloud by the surrounding protogalactic medium and therefore on the location of the cloud in the protoGalaxy. Since there is no significant (if any) metallicity gradient in the whole halo, we also present a review in favour of a galactic halo partly build via accretions and mergers of satellite systems. Some of them bear their own globular clusters and therefore ``contaminate'' the system of globular clusters formed ``in situ'', namely within the original potential well of the Galaxy. Therefore, the comparison between our self-enrichment model and the observational data should be limited to the genuine galactic globular clusters, the so-called Old Halo group.Comment: 11 pages, 4 figures, accepted for publication in Astronomy and Astrophysic

    Orchestrating innovation with user communities in the creative industries

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    International audienceThe digital creative industries exemplify innovation processes in which user communities are highly involved in product and service development, bringing new ideas, and developing tools for new product uses and environments. We explore the role of user communities in such co-innovation processes via four case studies of interrelations between firms and their communities. The digitization and virtualization of firm/community interactions are changing how boundaries are defined and how co-innovation is managed. The transformation of innovation management is characterized by three elements: opening and redefining firm boundaries; opening of products and services to community input and reducing property rights; and reshaping organization and product identities. Innovation in collaboration with user communities requires firms to orchestrate their communities and their inter-relationships to encourage the creativity and motivation of users, and develop the community's innovatory capacity
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