Archives Séminaires 2011-2012

Séminaire

Séminaire IPAG de Thierry Foglizzo (CEA Saclay), jeudi 27 janvier 2011 à 11h00, IPAG seminar room

Massive stars end their life with the gravitational collapse of their core and the formation of a neutron star. Their explosion as a supernova depends on the revival of a spherical accretion shock, located in the inner 200km and stalled during a few hundred milliseconds. Numerical simulations suggest that an asymmetric explosion is induced by a hydrodynamical instability named SASI. Its non radial character is able to influence the kick and the spin of the resulting neutron star. I will (...)

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Séminaire IPAG de Myriam Benisty (MPIA Heidelberg), jeudi 3 février 2011 à 9h30, IPAG seminar room

Understanding the physical conditions in the innermost circumstellar environments of young stars is a crucial step to comprehend planet formation and evolution. To do so, one needs to access the first astronomical unit (AU) surrounding the young star, and the only technique that can reach the required milli-arcsecond resolution is optical interferometry.
In this talk, I will present recent studies based on AMBER/VLTI observations of intermediate-mass young stars (the Herbig AeBe stars). (...)

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Séminaire IPAG de Patrick Hennebelle (LERMA Paris), jeudi 10 février 2011 à 11h00, IPAG seminar room

Star formation is one of the important problems of the modern astrophysics. Amongst many questions, understanding the initial mass function of stars (IMF), that is how the number of stars vary with mass, is tremendously important and along the years, several theories have been proposed to ex- plain the IMF. More recently, numerical simulations of supersonic turbulence including self-gravity have obtained IMF which resemble the observed one. However, understanding what is exactly happening (...)

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Séminaire IPAG de David Ehrenreich (IPAG), jeudi 17 février 2011 à 11h00, IPAG seminar room

Hot neptunes are a class of exoplanets with typical masses around 20x Earth. They are the link between hot gaseous giant exoplanets (or hot jupiters) and super-earths (between 1 and 10 Earth masses). It is surmised that the latters can be evaporation remnants, with atmospheres completely eroded by the extreme stellar irradiation. Meanwhile, it also appears that hot jupiters are stable with respect to atmospheric evaporation. In this case, what could be the progenitors of hot rocky planets (...)

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Séminaire IPAG de Louis d’Hendecourt (IAS Orsay), jeudi 24 février 2011 à 11h00, IPAG seminar room

L’origine de l’asymétrie biomoléculaire sur la Terre a fait l’objet de très nombreuses études théoriques et parfois expérimentales mais n’avait jamais été précisément abordé dans un cadre astrophysique réaliste. L’expérience Chiral-MICMOC de l’IAS, menée depuis 2003, a fini par obtenir des résultats probants : la création d’excès énantiomériques significatifs imbriqués dans la matière organique obtenue par photo/thermochimie d’analogues de glaces interstellaires à l’aide de rayonnement UV polarisé circulairement (...)

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Séminaire IPAG de Ryan C.G. Chaves (MPIA Heidelberg), jeudi 3 mars 2011 à 11h00, IPAG seminar room

Our understanding of the Galaxy in the very-high-energy gamma-ray domain has dramatically improved since the inception of the H.E.S.S. Galactic Plane Survey in 2004. The four H.E.S.S. imaging atmospheric Cherenkov telescopes in Namibia are highly sensitive to gamma rays above 0.1 TeV and feature a large 5-degree field-of-view, making them especially suited for large surveys. From their vantage point in the southern hemisphere, the H.E.S.S. telescopes have detected an unexpectedly large and (...)

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Séminaire IPAG de Nicolas Bouche (University of California), jeudi 17 mars 2011 à 11h00, IPAG seminar room

Globally, the efficiency to form galaxies is low, only 5% of the baryons made it into stars. Moreover, this efficiency is a strong function of mass, and peaks at around 20% for halos similar to the Milky Way. What causes this efficiency to decline in low mass galaxies ? Feedback is traditionally attributed to this for various reasons. We will address this issue from the point of view of the scaling relations. Indeed, galaxies form stars along a tight sequence, that evolves with redshift. We (...)

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Séminaire IPAG de Michel Aurière (IRAP, Toulouse), jeudi 24 mars 2011 à 11h00, IPAG seminar room

When an intermediate mass star is evolving off the main sequence, its radius increases and its rotational velocity is reduced, and a convective envelope is created which deepens. The red giant branch therefore appears as crucial to study the interplay of the magnetic fields and stellar evolution, since parameters directly connected to the production of surface magnetic fields are greatly modified.
I will present a survey of about 40 RGB and AGB stars which appeared good candidates to host (...)

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Séminaire IPAG de Hervé le Coroller (OAMP, Marseille), jeudi 31 mars 2011 à 11h00, IPAG seminar room

Carlina is an interferometer working in the visible wavelength and configured like a diluted version of the Arecibo radiotelescope. Above the diluted primary mirror, made of fixed co-spherical segments, a helium balloon, or cables suspended between two mountains, carries a gondola containing the focal optics, and detector. We are building at Observatoire de Haute-Provence a technical demonstrator of this diluted telescope. Acquiring stellar fringes is the main difficulty for astronomical (...)

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Séminaire IPAG de Richard Nelson (Queen Mary, University of London), jeudi 7 avril 2011 à 11h00, IPAG seminar room

In this talk I will present recent results concerning the dynamical evolution of planetesimals and planets embedded in protoplanetary discs. The talk will focus in particular on the dynamical stirring of planetesimals in discs with and without dead zones, and the implications for the collisional growth of these bodies, and their radial diffusion throughout the disc during the planet formation epoch. I will also present recent results of simulations that examine the migration torques (...)