Séminaire, par Vincent Bourrier
Jeudi 24 avril 2014, 14:30, salle Daniel Chalonge (entresol)
Characterization of planetary atmospheres outside our solar system has been carried out using observations of transiting planets. In particular, Lyman-alpha observations of atomic hydrogen in the atmospheres of HD209458b and HD189733b revealed that hot-Jupiters can "evaporate", their extended atmospheres losing significant amounts of gas into space. Heavier elements were also identified at high altitudes around these planets, showing that their strongly irradiated upper atmospheres expand at velocities reaching several kilometers per second. I will present new results that confirm this "blow-off" of HD209458b atmosphere: transit observations in the MgI line revealed signatures of neutral magnesium in the transition region between the thermosphere and the exosphere, while surprisingly no atmospheric absorption was found in the MgII doublet. I developed a 3D particle model of the dynamics of neutral and ionized magnesium populations, coupled with an analytical modeling of the thermosphere, to reproduce these observations. The analysis of transit absorption profiles in the magnesium lines constrain not only the exosphere properties, but also provides unprecedented information on the physical conditions at the altitude where the atmospheric blow-off takes place. The model of atmospheric escape has also been used to estimate the absorption signatures of all transiting planets in the MgI line. Thus, I identified a sample of exoplanets with a high detectability in MgI, which allow to anticipate further steps in comparative exoplanetology in a near future.
Magnesium: a new probe of exoplanets' extended atmospheres
Characterization of planetary atmospheres outside our solar system has been carried out using observations of transiting planets. In particular, Lyman-alpha observations of atomic hydrogen in the atmospheres of HD209458b and HD189733b revealed that hot-Jupiters can "evaporate", their extended atmospheres losing significant amounts of gas into space. Heavier elements were also identified at high altitudes around these planets, showing that their strongly irradiated upper atmospheres expand at velocities reaching several kilometers per second. I will present new results that confirm this "blow-off" of HD209458b atmosphere: transit observations in the MgI line revealed signatures of neutral magnesium in the transition region between the thermosphere and the exosphere, while surprisingly no atmospheric absorption was found in the MgII doublet. I developed a 3D particle model of the dynamics of neutral and ionized magnesium populations, coupled with an analytical modeling of the thermosphere, to reproduce these observations. The analysis of transit absorption profiles in the magnesium lines constrain not only the exosphere properties, but also provides unprecedented information on the physical conditions at the altitude where the atmospheric blow-off takes place. The model of atmospheric escape has also been used to estimate the absorption signatures of all transiting planets in the MgI line. Thus, I identified a sample of exoplanets with a high detectability in MgI, which allow to anticipate further steps in comparative exoplanetology in a near future.