Archives Séminaires 2014-2015

Séminaire

Séminaire IPAG de Ajit Kembahavi (Pune University), jeudi 18 septembre 2014 à 11h00, IPAG seminar room

The bulges in galaxies have generally been considered to be very similar to elliptical galaxies, in their morphology, stellar content and origin. But it has been known that bulges in late type galaxies can be disk like and contain features such as spiral arms, bars and rings, which point to continued star formation. These pseudo-bulges are thought to be formed due to the transfer of gas to the central regions of galaxies through non-axisymmetric structures like bars. It is now known that (…)

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Séminaire IPAG de Gaël Cessateur (PMOD/WRC), jeudi 25 septembre 2014 à 11h00, IPAG seminar room

The solar UV irradiance is one of a key parameters for space weather and space climate studies. Thorough several examples, I will show how the knowledge of the solar UV variability is of a great importance. I will also present a new model of solar irradiance variability for short term variations, COSIR for Code Of Solar Irradiance Reconstruction. Based on the assumption that the variability is triggered by the solar surface magnetism, we consider four types of active features such as sunspot (…)

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Séminaire IPAG de David Cebron (ISTERRE), jeudi 2 octobre 2014 à 11h00, IPAG seminar room

Tidally driven flows have been suggested to play a role in different fields of planetary and stellar dynamics, namely their surface patterns ans shapes (e.g. Jupiter stripes), their rotational dynamics (e.g. synchronization), and the processes of dynamo generation. However, the nature of the driven flows remains uncertain. In this talk, I propose that the so-called elliptical instability can be a key ingredient to drive these flows. This hydrodynamic instability, arising in rotating flows (…)

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Séminaire IPAG de Marta Volonteri (IAP), jeudi 9 octobre 2014 à 11h00, IPAG seminar room

Black holes are the engines that power quasars and active galactic nuclei throughout cosmic time. The masses of black holes in nearby galaxies define clear correlations with the properties of their host galaxies. These results suggest that black holes, while a thousand times lighter than the galaxy, grow alongside their hosts during its cosmic evolution. I will present theoretical models of the growth of black holes, and discuss the establishment of the connection between galaxies and black (…)

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Séminaire IPAG de Jérôme Guilet (MPA), jeudi 16 octobre 2014 à 11h00, IPAG seminar room

If a large-scale poloidal magnetic field is present in protoplanetary discs, it could have important dynamical consequences : the launching of a jet or a wind, a more vigorous MHD turbulence in the outer parts of the disc, or the quenching of turbulence at smaller radii. It could also influence the migration of protoplanets in the disc. The structure and strength of the magnetic field is, however, poorly known from both observational and theoretical points of view. I will describe a (…)

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Séminaire IPAG de Gregg Wade (RMC), jeudi 23 octobre 2014 à 11h00, IPAG seminar room

Since 2002, strong, organized magnetic fields have been firmly detected at the surfaces of about 10 Galactic O-type stars. In this talk I will review the characteristics of the inferred fields of individual stars, as well as the overall population. I will discuss the extension of the “magnetic desert”, first inferred among the A-type stars, to O stars up to 60 solar masses. I will discuss the interaction of the winds of the magnetic stars with the fields above their surfaces, generating (…)

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Séminaire IPAG de Maryvonne Gerin (LERMA), jeudi 6 novembre 2014 à 11h00, IPAG seminar room

C+ is the main reservoir of carbon in the diffuse interstellar medium. The Herschel satellite has enabled high spectral resolution observations of the fine structure line [CII] at 1.9 THz in a wide variety of sources. In this talk, I will present absorption measurements of the [CII] fine structure line soundinfg the diffuse interstellar medium long sight-lines towards massive star forming regions. These data are combined with Herschel data of the fine structure lines of atomic oxygen and (…)

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Séminaire IPAG de Patrick Eggenberger (Observatoire de Genève), jeudi 13 novembre 2014 à 11h00, IPAG seminar room

Asteroseismic data obtained by recent space missions have led to the detection and characterization of solar-like oscillations for a large number of stars. This has opened the way to the determination of the global and internal poperties of these stars, which is of prime importance to progress in our understanding of the internal transport of angular momentum and chemical elements. In this presentation, we discuss which constraints can be brought by these asteroseismic measurements on the (…)

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Séminaire IPAG de Mario Flock (CEA), jeudi 27 novembre 2014 à 11h00, IPAG seminar room

In this seminar I present recent results regarding the dynamics and thermodynamics of gas and dust in magnetized and turbulent protoplanetary disks.
I will focus on the inner and outer regions of protoplanetary disks. To study the inner disk regions, we developed a radiative transfer module, based on the flux-limited diffusion approximation that includes frequency dependent irradiation and dust opacities. We present results of the first global 3D radiation magneto-hydrodynamic simulations (…)

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Séminaire IPAG de Susmita Chakravorty (IPAG), jeudi 11 décembre 2014 à 11h00, IPAG seminar room

Signatures of photoionised outflows are found in the high resolution soft X-ray spectra (.3 - 3 keV) of active galactic nuclei (AGN). Conventionally called the warm absorber (WA), they are still poorly understood, after 30 years of its discovery. We still do not know how dense this gas is and where it is located in the AGN system ! Understanding how these outflows are launched or how they impact feedback are important to understand some of the basic functioning of the active super-massive (…)