Averaging on the motion of a fast revolving body. Application to the stability study of a planetary system

International audienceExploring the global dynamics of a planetary system involves computing integrations for an entire subset of its parameter space. This becomes time-consuming in presence of a planet close to the central star, and in practice this planet will be very often omitted. We derive for this problem an averaged Hamiltonian and the associated equations of motion that allow us to include the average interaction of the fast planet. We demonstrate the application of these equations in the case of the mu Arae system where the ratio of the two fastest periods exceeds 30. In this case, the effect of the inner planet is limited because the planet's mass is one order of magnitude below the other planetary masses. When the inner planet is massive, considering its averaged interaction with the rest of the system becomes even more crucial

Finding Stable Fits for Extrasolar Planetary Systems

International audienceSeveral problems with radial velocity determination of orbital elements call for dynamical studies. One of them is that, due to uncertainties in radial velocity data and complex dynamical behavior, the best fit obtained for systems with planets experiencing strong interactions, like HD202206 and HD160691, are most often not stable. For those two systems, we show how a careful stability analysis constrained by chi2 from radial velocity data (mostly from the Geneva Observatory research team) can lead to a stable fit

Contraindre les paramètres orbitaux des planètes extrasolaires en combinant les mesures de vitesses radiales, avec une étude dynamique du système

National audienc

Contraindre les paramètres orbitaux des planètes extrasolaires en combinant les mesures de vitesses radiales, avec une étude dynamique du système

National audienc

A simple ionospheric correction method for radar-based space surveillance systems, with performance assessment on GRAVES data

Ionospheric effects degrade the quality of radar data, which are critical for the precision of the satellite ephemeris produced by space surveillance systems; this degradation is especially noticeable for radars such as GRAVES that operate in the very high frequency range. This article presents a simple and effective method to correct for ionospheric effects, with an evaluation on data obtained with GRAVES, the French space surveillance radar. This method relies on GPS data, and our evaluation relies on GRAVES and DORIS data. We found that the gain in terms of evaluated radial velocity can be as high as 1.76$\kappa$, where $\kappa$ is the typical root mean square of the noise on radial velocity measurements for GRAVES (excluding ionospheric effects): the error decreases from 2.60$\kappa$ to 0.83$\kappa$ for daytime satellite overhead passes. Our conclusion is that, while this method is very simple to implement, it has proven to be a good correction for ionospheric effects in practice.Comment: Accepted for publication in Advances in Space Research. 6 pages, 4 figure