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Accueil > Le Laboratoire > Séminaires et conférences > Past Seminars > Résumés 2012-2013

 Résumés 2012-2013

15 March 2013 - 11h

  • Héloïse Meheut (CEA Saclay)
  • The Rossby Wave Instability : From Microquasars to Planets

The most challenging step in planet formation theory is to explain the formation of planetesimals of kilometre size. A promising scenario involves the existence of vortices able to concentrate a large amount of dust grains in their centres and to accelerate the growth of the solids.
Here we are interested in the Rossby wave instability that can form vortices against the shearing effect of differential rotation. I will present numerical simulations of this instability, initially performed in the context of microquasars accretion disks and emission of jets. I will then show why the unexpected results of these simulations were applied to the study of protoplanetary disks and how it modified our understanding of planetesimals formation.

19 Oct 2012 - 11h

  • Stéphanie Juneau (CEA Saclay)
  • Hidden Supermassive Black Holes in Star-Forming Galaxies

While it is clear that gas fuels both star formation and nuclear activity in galaxies, the connection between the growth of their stellar content and that of their central supermassive black hole remains under debate. Previous surveys attempting to address this issue have been biased against obscured and/or moderate luminosity systems therefore only allowed us to sketch a partial picture, and an incomplete census of all the phases of black hole growth.
Do the stars and central black hole grow in lock-step ? What are the governing physical processes ? I will present a new AGN selection method and a few surprises that were revealed upon its application, including : (i) a high fraction of active galactic nuclei (AGN) in star-forming galaxies at intermediate redshifts, (ii) connections between obscuration of the central engine and the host galaxies, linking the very small scale fueling region (sub-parsec) to an impressive variety of physical scales (perhaps up to kpc) within the surrounding galaxy, and (iii) a new mode of black hole growth in galaxies.
I will discuss the implications of these results. Will we witness a shift in paradigm regarding the connection between galaxies and their central black hole ?

28 Sep 2012 - 11h

  • Jean-Claude Bouret (LAM)
  • Massive Stars at Low Metallicity : Evolution and Surface Abundances of O Dwarfs in the SMC

We have studied the properties of massive stars at low metallicity, with an emphasis on their evolution, rotation, and surface abundances. We focussed on O-type dwarfs in the Small Magellanic Cloud (SMC). Such stars are expected to have weak winds that do not remove significant amounts of the stars’ initial angular momentum. We have modeled the UV and optical spectra of twenty-three objects and derived photospheric and wind properties.
I will present the results we obtained concerning the binary fraction of the sample, the properties of fast rotators and the constraints we obtained on the level of rotational mixing, which can be compared to predictions from stellar evolution models.

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