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Séminaire MHD (SEMHD)

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Détection des planètes extra-solaires par émission d’ondes radio
Philippe Zarka (CNRS)

24 novembre 2008

Planet-star plasma interaction can be described as the interaction of a plasma flow with an obstacle, each being possibly magnetized. Examples of the four possible situations are found in our Solar system, with an intense radio emission being produced in three cases out of four, when either the flow or the obstacle is strongly magnetized. Scaling laws are derived which relate the emitted radio power to that dissipated in the various corresponding flow-obstacle interactions. They are generalized as a "radio-magnetic" scaling law between the output radio power and the magnetic energy flux convected onto the obstacle.
Extrapolating to the case of exoplanets, we find that hot Jupiters may produce a very intense radio emission due to planetary magnetospheric interaction with a strong stellar wind, reconnection between planetary and stellar magnetic fields, or unipolar interaction between the planet and a magnetic star (or strongly magnetized regions of the stellar surface). The emitted radio power is expected in the hecto-decameter range with intensities 1E3 to 1E6 times that of Jupiter (unless some "saturation" mechanism is at work). Corresponding flux densities should be detectable at the ten-parsec range with modern radio arrays. We briefly discuss ongoing observational searches as well as the interests of direct radio detection.
Bibliographie :
– Griessmeier J.-M., Zarka P., and Spreeuw H., "Predicting low-frequency radio fluxes of known extrasolar planets", Astron. Astrophys., 475 (2007), 359–368.
– Jardine M., and Cameron A.C., "Radio emission from exoplanets: The role of the stellar coronal density and magnetic field strength", Astron. Astrophys., 490 (2008), 843–851.
– Zarka P., "Auroral radio emissions at the outer planets: Observations and theories", J. Geophys. Res., 103 (1998), 20159–20194.
– Zarka P., "Plasma interactions of exoplanets with their parent star and associated radio emissions", Planet. Space Sci., 55 (2007), 598-617.

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Philippe Zarka Philippe Zarka (CNRS)
Laboratoire d’Études Spatiales et d’Instrumentation en Astrophysique (LESIA, UMR CNRS 8109).