Mardi 13 dĂ©cembre 2011 à 11h00 (Amphithéâtre du bât. 18)
Pierre Drossart (LESIA)
Tuesday 6 December 2011 à 11h00 (Salle de confĂ©rence du bât. 17)
Keiichi Ohnaka (Max Planck Institute for Radio Astronomy, Bonn)
We present spatially resolved high-spectral resolution observations of the 2.3 micron CO first overtone lines in the red supergiant Betelgeuse using AMBER at the Very Large Telescope Interferometer (VLTI). For the first time, we have succeeded in reconstructing spatially resolved spectra of the individual CO lines for the inhomogeneous, dynamical atmosphere with a spectral resolution of 6000 and a spatial resolution of 9.8 mas — the highest spatial resolution achieved for Betelgeuse. The observed spatially resolved spectrum reveals a pronounced, asymmetrically extended atmosphere up to at least 1.3 stellar radii. Moreover, the extended atmosphere appears differently across the CO line profiles because of the vigorous motions of a large CO gas clump with velocities of 20—30 km/s. Comparison between the CO line data taken in 2008 and 2009 shows a significant change in the dynamics of the atmosphere. In contrast to the CO line data, the continuum data taken in 2008 and 2009 reveal no or only marginal time variations, much smaller than the maximum variation predicted by the current 3-D convection simulations. Our AMBER observations suggest the following new picture: the material within 1.5 stellar radii is strongly stirred possibly by magnetohydrodynamical processes or pulsation and may be violently flung out rather than spilling out in an ordered, spherical fashion as often assumed.
Friday 25 November 2011 à 11h00 (Salle de confĂ©rence du bât. 17)
Abraham Chian (LESIA & National Institute for Space Research, Sao Jose dos Campos-SP, Brazil)
Lecture 4/4 of a series of open lectures on “Nonlinear dynamics of the stellar-planetary environment".
Reference : PRL 91, 034102 (2003); PRL 98, 014101 (2007); PRL 104, 254102 (2010)
Tuesday 8 November 2011 à 11h00 (Salle de confĂ©rence du bât. 17)
Denis Defrère (Université de Liège)
Most debris disks resolved so far show extended structures located at tens to hundreds AU from the host star, and are more analogous to our solar system’s dusty Kuiper belt than to the AU-scale zodiacal disk inside our solar system’s asteroid belt. Over the last few years however, a few hot debris disks have been resolved around a handful of main sequence stars thanks to the advance of infrared interferometry. The grain populations derived from these observations are quite intriguing, as they point toward very high dust replenishment rates, high cometary activity or major collisional events. In this talk, we review the ongoing effort to detect bright exozodiacal disks with precision near-infrared interferometry at the CHARA array with the FLUOR instrument. We discuss preliminary statistical trends on the occurrence of bright exozodiacal disks around nearby main sequence stars and show how this information can be used to constrain the global architecture and evolution of debris disks. Finally, we briefly address near-term prospects by discussing the ongoing instrumental developments of the FLUOR instrument.
Monday 7 November 2011 à 11h00 (Salle de confĂ©rence du bât. 17 )
Abraham Chian (LESIA & National Institute for Space Research, Sao Jose dos Campos-SP, Brazil)
Lecture 3/4 of a series of open lectures on “Nonlinear dynamics of the stellar-planetary environment".
Reference : ApJL 330, L77 (1988); PSS 48, 9 (2000); A&A 390, 351 (2002); ASR 46, 472 (2010)
Wednesday 26 October 2011 à 16h00
Geoff Marcy (University of California, Berkeley)
The talk will report the observed distribution of planet radii, orbital distances, and occurrence frequency for planets with orbital periods less than 50 days around Solar-type stars. We draw from extensive Kepler measurements that offer good completeness for planets with radii as small as 2.0 Earth-radii.
Wednesday 26 October 2011 à 14h00 (Salle de confĂ©rence du bât. 17)
Geoff Marcy (University of California, Berkeley)
The talk will report the observed distribution of planet radii, orbital distances, and occurrence frequency for planets with orbital periods less than 50 days around Solar-type stars. We draw from extensive Kepler measurements that offer good completeness for planets with radii as small as 2.0 Earth-radii.
Mardi 18 octobre 2011 à 11h00 (Salle de confĂ©rence du bât. 17)
David Ehrenreich (IPAG, Grenoble)
More than 600 extrasolar planets have been detected so far and an intense characterisation effort has been undertaken to unveil the atmospheric properties of some of these distant worlds seen in transit accross their stars. A large number of transiting exoplanets are found in extreme irradiation environments, very close to their stars, and the question arise of whether the atmospheres of these planets remain stable or get blown away. Atmospheric evaporation was observed in some hot giant exoplanets or "hot jupiters", but does not significantly alter the fate of these massive objects ( 300 Earth masses). Hot neptunes, on the other hand, are a class of exoplanets with typical masses around 20x Earth. They are the link between hot jupiters and super-earths (1 to10 Earth masses). It is surmised that the latters can be evaporation remnants, with atmospheres completely eroded by the extreme stellar irradiation. In this case, could hot neptunes be the progenitors of the hot rocky planets detected by the Corot and Kepler missions ? Detecting their extended atmospheres and measuring their mass loss rates and atmospheric heating efficiencies are key steps towards the understanding of the atmospheric dynamics and properties of low-mass exoplanets. After an introduction about planetary transits, I will review the results we have obtained with HST on the atmospheric evaporation of transiting exoplanets, on both observational and theoretical sides. I will finally discuss the prospects about atmospheric characterisation for Earth-size planets in more temperate - habitable - environments, and how the upcoming transit of Venus in June 2012 and the PLATO mission proposed to ESA could lead to a new era where atmospheric characterisation is common for hundreds of Earth-like exoplanets.
Seminar in french
Friday 14 October 2011 à 11h00 (Salle de confĂ©rence du bât. 17)
Abraham Chian (LESIA & National Institute for Space Research, Sao Jose dos Campos-SP, Brazil)
Lecture 2/4 of a series of open lectures on “Nonlinear dynamics of the stellar-planetary environment".
Reference : JGR 111, A07S03 (2006); NPG 14, 17 (2007); AG 27, 1789 (2009)
Monday 10 October 2011 à 11h00 (Salle de confĂ©rence du bât. 17)
Margaret Kivelson (UCLA)
Electromagnetic phenomena in Saturn’s magnetosphere and ionosphere vary periodically at a period close to that of planetary rotation. Arguments relating to the slow drift of the modulation period and the inertia of different regions of Saturn’s environment require that the system be driven from regions remote from the equatorial surface, plausibly the high altitude atmosphere. The assumption that the system is driven from the ionospheric ends of the flux tubes is supported by characteristics of the magnetic perturbations observed near the magnetic equator. This presentation will describe results from a magnetohydrodynamic simulation in which the atmosphere drives vortical winds in the southern ionosphere. The wind pattern rotates about the spin axis at the modulation period of Saturn Kilometric Radiation (SKR). The simulation reproduces many features reported for magnetospheric perturbations. It also exhibits field-aligned current (FAC) patterns that correspond to properties reported for SKR emissions. In a second run of the simulation, an additional vortical flow structure is introduced into the northern high-altitude atmosphere. The northern structure rotates about the spin axis at a slightly shorter period. This second simulation provides insight into the way in which two separate frequencies affect the magnetosphere and the FACs.
Co-authors: Xianzhe Jia and Tamas Gombosi
