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Session PNP

Dynamical parameters determination in multiple systems
Beauvalet L., Lainey V., Arlot J.-E.
(IMCCE-Observatoire de Paris)
Many Kuiper Belt Object and asteroids have now been discovered to be part of more complex dynamical systems consisting of a primary and its satellites. In this case, the primary's motion is not strictly keplerian around the Sun since the influence of its companions disturbs its trajectory. We present a model which will allow for a global solution when fitting the orbital parameters to astrometric observations. The goal of this work is to be able to constrain the masses and other dynamical parameters in this kind of system. The multiple system which has been studied for the longest time and would then make a perfect candidate is Pluto's one, with its binary Pluto/Charon and its smaller satellites. Our model has been tested on simulated observations of Pluto's system in order to determine the parameters which can be properly determined.

Search and characterization for extrasolar planets in the Northern hemisphere with the SOPHIE consortium
I. Boisse, F. Bouchy, G. Hébrard, S. Udry, X. Delfosse, C. Moutou, A-M. Lagrange, D. Queloz et al.
(Institut d'Astrophysique de Paris)
The SOPHIE Consortium started, in Nov. 2006, several programs of exoplanet search and characterization in the North hemiphere with the spectrograph SOPHIE based on the 1.93m OHP telescope. We present here the latest SOPHIE results which include new exoplanets, studies of transiting planets through Rossiter effect, follow-up observations of photometric surveys and characterizations of stellar activity of planet-host stars.

A collisionless scenario for Uranus tilting
BOUE Gwenaël & LASKAR Jacques
(IMCCE - Obs. de Paris)
The origin of the high inclination of Uranus' spin-axis (Uranus' obliquity) is one of the great unanswered questions about the Solar system. Giant planets are believed to form with nearly zero obliquity, and it has been shown that the present behaviour of Uranus' spin is essentially stable. Several attempts were made in order to solve this problem. Here we report numerical simulations showing that Uranus' axis can be tilted during the planetary migration, without the need of a giant impact, provided that the planet had an additional satellite and a temporary large inclination. This might have happened during the giant planet instability phase described in the Nice model. In our scenario, the satellite is ejected after the tilt by a close encounter at the end of the migration. This model can both explain Uranus' large obliquity and bring new constraints on the planet orbital evolution.

Coupling dynamical and collisional evolution of dust in circum-stellar disks
S. Charnoz, L. Fouchet, E. Di-Folco, E. Pantin
(Laboratoire AIM, Université Paris Diderot /CEA/CNRS)
Numerous observed circumstellar disks are believed to be both dynamically and collisionally active. Unfortunately planets and large bodies that could be embedded in are still difficult to observe and their putative properties are indirectly inferred from the observable dusty content. It is why constraining the size distribution coupled with dust-dynamics is so critical. Unfortunately, coupling effects such as a realistic time-dependant dynamics, fragmentation and coagulation, has been recognized as numerically challenging and almost no attempt really succeeded with a generic approach. In these disks, the dust dynamics is driven by a variety of processes (gravity, gas drag, radiation pressure, Poynting-Robertson effect etc..) inducing a size-dependant dynamics, and, at the same time collisional evolution induces a progressive change of the local size distribution. These two effects are intimately coupled because the local dynamics and size-distribution determines the local collision rates, that, in-turn, determines the size-distribution and modifies the particle's dynamics. Here we report on a new algorithm that overcomes these difficulties by using a hybrid approach extending the work of Charnoz & Morbidelli (Icarus, 2004, 2007). We will briefly present the method and focus on : (1) gaseous protoplanetary disks either laminar or turbulent (the time dependant transport and dust evolution will be shown) and (2) post-planetary disks with or without planets in which we will map the regional size distributions of micrometer dust.

ASTEP: Towards the detection and characterization of exoplanets from Dome C
Crouzet N., Guillot T., Agabi A., Rivet J.-P., Bondoux E., Challita Z., Fanteï-Caujolle Y., Fressin F., Mékarnia D., Schmider F.-X., Valbousquet F., Blazit A., Bonhomme S., Abe L., Daban J.-B., Gouvret C., Fruth T., Rauer H., Erikson A., Barbieri M., Aigrain S. and Pont F.
(Observatoire de la Côte d'Azur)
The Concordia base in Dome C, Antarctica, is an extremely promising site for photometric astronomy due to the 3-month long night during the Antarctic winter, favorable weather conditions, and low scintillation. The ASTEP project (Antarctic Search for Transiting ExoPlanets) is a pilot project to discover transiting planets, and understand the limits of visible photometry from this site. ASTEP South is the first phase of the project. The instrument is a fixed 10 cm refractor with a 4k x 4k CCD camera in a thermalized box, pointing continuously a 3.88^ x 3.88^ field of view centered on the celestial south pole. The instrument observed nearly continuously during the 2008 and 2009 Antarctic winters, and the data are of good quality. The weather conditions are estimated from the number of stars detected in the field. For the 2008 winter, the statistics are between 56.3% and 68.4% of excellent weather, 17.9% to 30% of veiled weather and 13.7% of bad weather. Using these results, we show that the detection efficiency of transiting exoplanets in one given field is improved at Dome C compared to a temperate site such as La Silla. This shows the high potential of Dome C for photometry and future planet discoveries (Crouzet et al. A&A 2010). The second phase of the project is ASTEP400, an equatorial 40 cm telescope entirely designed and built for photometry under the extreme conditions of the Antarctic winter. The instrument is now installed at Concordia and the first campaign started in March 2010.

SMART-1 new results and future lunar exploration
Bernard H. Foing (ESA/ESTEC)
SMART-1 Small Mission for Advanced Research and Technology [1-7].achieved its first objective to demonstrate Solar Electric Primary Propulsion (SEP) for future Cornerstones (such as Bepi-Colombo) and to test new technologies for spacecraft and instruments. SMART-1 science payload, with a total mass of some 19 kg, featured advanced technologies, and innovative instruments with a miniaturised high-resolution camera (AMIE) for lunar surface imaging, a near-infrared point-spectrometer (SIR) for lunar mineralogy investigation, and a very compact X-ray spectrometer (D-CIXS) for fluorescence spectroscopy and imagery of the Moon's surface elemental composition. We present a synthesis of lessons learned, technologies and exploration results from SMART-1, as a contribution to the preparation of subsequent missions. We shall review the highlights with focus on recent published results. SMART-1 has been useful in the preparation of Selene Kaguya, the Indian lunar mission Chandrayaan-1, Chinese Chang'E 1, the US Lunar Reconnaissance Orbiter, LCROSS, and subsequent lunar landers. SMART-1 has been contributing to planetary science [3-6], and helped to prepare the next steps for exploration: survey of resources, monitoring polar illumination, and mapping of sites for potential landings, robotic villages and for future international lunar bases. Links:, References: [1] Racca, G.D. et al. (2002) P&SS, 50, 1323. [2] Foing, B.H. et al (2003) Adv. Space Res., 31, 2323. [3] Foing B.H. et al (2006) Adv Space Res, 37, 6. [4] Grande, M. et al. (2003) P&SS, 51, 427. [5] Grande, M. et al (2007) P&SS 55, 494. [6] Pinet, P. et al (2005) P&SS, 53, 1309. [7] Josset J.L. et al (2006) Adv Space Res, 37, 14.

We thank G.Racca, D. Koschny, B. Grieger, J.-L. Josset, S. Beauvivre, M. Grande, J. Huovelin, H.U. Keller, U. Mall, A. Nathues, A. Malkki, G. Noci, Z. Sodnik, B. Kellett, P. Pinet, S. Chevrel, P. Cerroni, M.C. de Sanctis, M.A. Barucci, S. Erard, D. Despan, K. Muinonen, V. Shevchenko, Y. Shkuratov, M. Ellouzi, S. Peters, M. Almeida, D. Frew, J.Volp, D. Heather, P. McMannamon, O. Camino for their contribution to the SMART-1 project and instruments.

Is meridional circulation responsible for CAIs radial transport in proplanetary disks?
S. Fromang, W. Lyra
(CEA Saclay)
Calcium-Aluminum-rich Inclusions (CAIs) are the most primitive solids formed in our solar system. Because they condensed at high temperature, they are thought to have formed close to the sun. Yet, the discovery of CAIs in comets orbiting at large distances from the sun as reported by the Stardust mission suggests that CAIs were efficiently transported out to large radial distances in the solar nebula. Recently, a large scale meridional flow has been suggested as being responsible for that transport. Such a large scale flow naturally emerges out of viscous disk theories that are commonly used to model turbulence in protoplanetary disk. Here, I will use high resolution MHD simulations of global turbulent disk to investigate from first principles whether such flows indeed develops in turbulent accretion disks. Consequences of these simulations for the radial transport of CAIs will be discussed.

Combined stellar and planetary modeling
M. Havel T. Guillot
(Observatoire de la Côte d'Azur)
Transiting exoplanets are key to understanding planetary formation and evolution. However, the determination of their mass and size, and hence of their composition depends crucially on our ability to correctly infer the properties of their parent stars. Our goal is to investigate how uncertainties on stellar parameters and possible systematic effects in the modeling of stellar evolution impinge on planet characterization. We create an extensive grid of stellar models based on mass, chemical composition and input-physics, compare it with other widely used stellar models and perform a sensitivity test on planetary properties. In some cases such as CoRoT-2, we identify a new ensemble of solutions corresponding to the pre-main sequence evolution of the parent star that allow for a self-consistent solution accounting for the large planet size. On the other hand, CoRoT-9 is of special interest since it allows a validity check for planetary evolution models. We also revisit the question of the star-planet metallicity correlation in light of stellar evolution models for various metallicities.

A new model of cometary non-gravitational forces
L. Maquet, F. Colas, J. Crovisier, L.Jorda
(IMCCE-Observatoire de Paris)
The gravitational orbit of a comet is affected by the sublimation of water molecules by the nucleus when the comet approaches perihelion. This outgassing triggers a non-gravitational force (NGF) which significantly modifies the orbit of the comet. The amplitude of the perturbation depends on several parameters which can be constrained by visible, infrared and radio observations of the coma and nucleus of the comet. It depends also on the nucleus density, which can in turn be determined by modeling the effect of the NGF on the orbit of a comet. This method is the only method available so far to estimate the density of cometary nuclei. Up to now, the modeling of this effect is mostly based on an empirical model defined in the early 70's [1] which uses a simplified isotropic outgassing model. Attempts have been made to use advanced anisotropic thermal models to calculate the NGF taking into account several observational constraint and to retrieve the nucleus density [2], but: (i) this approach is restricted to a handful of cometary nuclei which are sufficiently well-known to allow this type of modeling, and (ii) the authors usually don't fit directly the astrometric measurements but rather « nongravitational parameters » calculated with the above-mentioned empirical model. We present a new model for non-gravitational forces with the aim of revisiting the problem of NGF calculation and nucleus density determination. The method is based on the separation of the surface of the nucleus in several surface elements located at different latitudes. The contribution of each surface element to the overall NGF is fitted from the astrometric measurements together with the density of the nucleus. This new method will be used to interpret future astrometric measurements of these pristine objects with GAIA.

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suivant: Poster contributions monter: sf2a_boa précédent: Poster contributions
Samuel Boissier 2010-06-16