1,680 research outputs found
The Self-Enrichment of Galactic Halo Globular Clusters: the mass-metallicity relation
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
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 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
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
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, . We vary 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 . 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, , is independent of the impact of the tidal field,
.Comment: accepted for publication in MNRAS, 8 pages, 5 figures,3 table
The Old Halo metallicity gradient: the trace of a self-enrichment process
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
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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