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Voss R.,Radboud University Nijmegen | Martin P.,Institute Of Planetologie Et Dastrophysique Of Grenoble | Diehl R.,Max Planck Institute for Extraterrestrial Physics | Vink J.S.,College Hill | And 2 more authors.
Astronomy and Astrophysics | Year: 2012

Aims. We study the populations of massive stars in the Carina region and their energetic feedback and ejection of 26Al. Methods. We did a census of the stellar populations in young stellar clusters within a few degrees of the Carina nebula. For each star we estimated the mass, based on the spectral type and the host cluster age. We used population synthesis to calculate the energetic feedback and ejection of 26Al from the winds of the massive stars and their supernova explosions. We used 7 years of INTEGRAL observations to measure the 26Al signal from the region. Results. The INTEGRAL 26Al signal is not significant with a best-fit value of ∼1.5 ± 1.0 × 10 -5 ph cm -2 s -1, approximately half of the published Compton Gamma Ray Observatory (CGRO) result, but in agreement with the latest CGRO estimates. Our analysis of the stellar populations in the young clusters leads to an expected signal of ∼half the observed value, but the results are consistent within 2σ. We find that the fraction of 26Al ejected in Wolf-Rayet winds is high, and the observed signal is unlikely to be caused by 26Al ejected in supernovae alone, indicating a strong wind ejection of 26Al. Due to the lack of prominent O stars, regions with ages ≳ 10 Myr are often neglected in studies of OB associations. We find that in the Carina region such clusters contribute significantly to the stellar mass and the energetics of the region. © 2012 ESO. Source

Parker R.J.,ETH Zurich | Andersen M.,Institute Of Planetologie Et Dastrophysique Of Grenoble
Monthly Notices of the Royal Astronomical Society | Year: 2014

We use N-body simulations to compare the evolution of spatial distributions of stars and brown dwarfs in young star-forming regions. We use three different diagnostics: the ratio of stars to brown dwarfs as a function of distance from the region's centre, RSSR, the local surface density of stars compared to brown dwarfs, ΣLDR, and we compare the global spatial distributions using the ΛMSR method. From a suite of 20 initially statistically identical simulations, 6/20 attain RSSR ≪ 1 and ΣLDR ≪ 1 and ΛMSR ≪ 1, indicating that dynamical interactions could be responsible for observed differences in the spatial distributions of stars and brown dwarfs in star-forming regions. However, many simulations also display apparently contradictory results - for example, in some cases the brown dwarfs have much lower local densities than stars (ΣLDR ≪ 1), but their global spatial distributions are indistinguishable (ΛMSR = 1) and the relative proportion of stars and brown dwarfs remains constant across the region (RSSR = 1). Our results suggest that extreme caution should be exercised when interpreting any observed difference in the spatial distribution of stars and brown dwarfs, and that a much larger observational sample of regions/clusters (with complete mass functions) is necessary to investigate whether or not brown dwarfs form through similar mechanisms to stars. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Vincent A.C.,McGill University | Martin P.,Institute Of Planetologie Et Dastrophysique Of Grenoble | Cline J.M.,McGill University
Journal of Cosmology and Astroparticle Physics | Year: 2012

We compare the full-sky morphology of the 511 keV gamma ray excess measured by the INTEGRAL/SPI experiment to predictions of models based on dark matter (DM) scatterings that produce low-energy positrons: either MeV-scale DM that annihilates directly into e +e - pairs, or heavy DM that inelastically scatters into an excited state (XDM) followed by decay into e +e - and the ground state. By direct comparison to the data, we find that such explanations are consistent with dark matter halo profiles predicted by numerical many-body simulations for a Milky Way-like galaxy. Our results favor an Einasto profile over the cuspier NFW distribution and exclude decaying dark matter scenarios whose predicted spatial distribution is too broad. We obtain a good fit to the shape of the signal using six fewer degrees of freedom than previous empirical fits to the 511 keV data. We find that the ratio of flux at Earth from the galactic bulge to that of the disk is between 1.9 and 2.4, taking into account that 73% of the disk contribution may be attributed to the beta decay of radioactive 26Al. © 2012 IOP Publishing Ltd and Sissa Medialab srl. Source

Bykov A.,RAS Ioffe Physical - Technical Institute | Gehrels N.,NASA | Krawczynski H.,Washington University in St. Louis | Lemoine M.,CNRS Paris Institute of Astrophysics | And 3 more authors.
Space Science Reviews | Year: 2012

In this review we confront the current theoretical understanding of particle acceleration at relativistic outflows with recent observational results on various source classes thought to involve such outflows, e.g. gamma-ray bursts, active galactic nuclei, and pulsar wind nebulae. We highlight the possible contributions of these sources to ultra-high-energy cosmic rays. © 2012 Springer Science+Business Media B.V. Source

Belehaki A.,Institute of Astronomy | Lilensten J.,Institute Of Planetologie Et Dastrophysique Of Grenoble
Journal of Space Weather and Space Climate | Year: 2013

Reaching the end of the second year of the Journal of Space Weather and Space Climate, we present an overview of important issues that resulted in the clarification of our editorial policy, mainly triggered by the response of the scientific communities related to SWSC. We conclude this editorial with future perspectives concerning the impact factor and the charging policy. © A. Belehaki et al., Published by EDP Sciences 2013. Source

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