Archives Séminaires 2011-2012

Séminaire

Séminaire IPAG de Benoît Commerçon (LERMA), jeudi 26 janvier 2012 à 11h00, IPAG seminar room

Stars are the main source of luminous matter in the Universe. By transforming gas and tiny dust particles into stars, star formation is a dominant process in the interstellar cycle. In addition, star formation is also crucial to understand planet formation and it shapes the evolution and the structure of galaxies. Consequently, it is of prime importance in astrophysics to understand how stars form. Although it is well established that stars form within molecular clouds via gravitational (…)

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Séminaire IPAG de Philippe Kopplin (Helmholtz Zentrum München), jeudi 9 février 2012 à 11h00, IPAG seminar room

Natural organic matter (NOM) occurs in soils, freshwater and marine environments, in the atmosphere and in the form of prebiotic organic matter and represents an exceedingly complex mixture of organic compounds that collectively exhibits a nearly continuous range of properties (size-reactivity continuum). The fate NOM in the bio- and geosphere is governed according to the rather fundamental restraints of thermodynamics and kinetics. In these intricate materials, the "classical" signatures of (…)

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Séminaire IPAG de Ulysse Marboeuf (IPAG), jeudi 23 février 2012 à 11h00, IPAG seminar room

Comets are the most primitive bodies in the solar system. Their study is important to understanding the conditions of formation of the solar system and determine its initial physico-chemical composition. However, many unknowns remain on the nature of these objects and experimental and theoretical studies must be conducted, in addition to the observations, to deduce their original physico-chemical composition. At the seminar, I will present the scientific objectives of the study of comets, (…)

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Séminaire IPAG de Pierrick Martin (IPAG), jeudi 1er mars 2012 à 11h00, IPAG seminar room

Our Galaxy gives rise and hosts several populations of non-thermal particles, distributed over large scales from the centre to the periphery and halo. These Galactic cosmic rays span energies from less than 100MeV to more than 100TeV and it is now commonly accepted that they are accelerated in the strong shocks that accompany some of the most violent astrophysical phenomena, although some aspects of the process remain currently unclear. Far from being a side effect of stellar evolution, (…)

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Séminaire IPAG de Juergen Steinecker (IPAG), jeudi 8 mars 2012 à 11h00, IPAG seminar room

What causes the onset of star formation in dense molecular cloud cores ? Which of the physical agents control the complex interplay of gravitation, gas dynamics, magnetic fields, cooling, and chemistry ? We do not know yet - there is no general paradigm that puts together the information from the different wavelength regimes and the outcome of the simulations.
Last year, a new source of information was revealed by the detection of the coreshine. Unexpectedly, the densest part of cores (…)

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Séminaire IPAG de Gijs Mulders (U. of Amsterdam), jeudi 15 mars 2012 à 11h00, IPAG seminar room

Protoplanetary disks are thought to be the main sites of planet formation, and to understand how planets form we need to understand the physical processes in these disks. Radiative transfer codes are able to explain a large variety of observations of these disks — both resolved and unresolved — and have become an important tool in modelling them. However, their fit parameters are not always connected to the physical processes we want to study. In this talk I will explain how we can learn (…)

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Séminaire IPAG de Ioanna Arka (IPAG) , jeudi 29 mars 2012 à 11h00, IPAG seminar room

Since the launch of the Fermi Gamma-Ray Space Telescope, the amount of gamma-ray pulsars has dramatically increased. The new observations have helped restrain current models of pulsar high-energy emission. However, magnetospheric models still face problems, mainly when trying to explain the GeV emission from millisecond pulsars. On the other hand, gamma-ray emission from the pulsar wind is still a viable alternative. In this talk I will argue that the solution to the problem might lie in a (…)

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Séminaire IPAG de Michael Meyer (ETH Zurich), jeudi 5 avril 2012 à 11h00, IPAG seminar room

Planets are thought to form from circumstellar disks of gas and dust which appear to be an inevitable outcome of the star formation process. Sophisticated models have been put forward to explain the bewildering diversity of planetary systems uncovered to date (including our own). Yet key aspects of these theories are unconstrained. We describe recent results from both ground- and space-based observational programs aimed at : a) defining the range of initial conditions to be assumed in these (…)

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Séminaire IPAG de Maxime Viallet (U. of Exeter), jeudi 26 avril 2012 à 11h00, IPAG seminar room

Convection is a key process in stellar interiors. It is characterized by large Reynolds numbers, implying a highly turbulent regime. I will show how multidimensional hydrodynamical simulations allow us to get a physical insight of this complex phenonemon. The numerical results are obtained with a fully implicit method, and in the talk I will present the general framework and discuss the advantages of implicit methods in tackling stellar hydrodynamical problems.

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Séminaire IPAG de Marc Chaussidon (CRPG, Nancy), jeudi 3 mai 2012 à 11h00, IPAG seminar room

Recent developments of high precision Mg isotopes measurements in meteorites show that short-lived 26Al can be used as a reliable chronometer of condensation, accretion and differentiation processes which took place in the first few million years in the accretion disk around the early Sun. Primitive meteorites contain components (Mg-rich olivines in type I chondrules) which from their Mg and O isotopic compositions could be fragments of planetesimals formed and disrupted early in the disk. (…)