Star-Planet Interactions in the Radio Domain: Prospect for Their Detection

International audienceAll possible types of interaction of a magnetized plasma flow with an obstacle (magnetized or not) are considered, and those susceptible to produce a radio signature are identified. The role of the sub-Alfvénic or super-Alfvénic character of the flow is discussed. Known examples in the solar system are given, as well as extrapolations to star-planet plasma interactions. The dissipated power and the fraction that goes into radio waves are evaluated in the frame of the radio-magnetic scaling law, the theoretical bases and validity of which are discussed in the light of recent works. Then it is shown how radio signatures can be interpreted, in the frame of the cyclotron-maser theory (developed for P. Zarka (

Magnetic Fields in Planet-Hosting Stars

International audienceThe stellar magnetic field is a prime ingredient in the interactions between a parent star and its planets. Impacts on the stellar surface or dynamo as well as on the planetary atmosphere and internal structure are expected from these interactions. The magnetic field also plays a huge role in the formation and evolution of the system. The magnetic properties of planet-host stars, however, are barely known. Although it is impossible to spatially resolve the stellar surface of any star other than the Sun, spectropolarimetry allows probing the global large-scale magnetic strength and orientation at a given time. Then, monitoring polarized signatures over time as the star rotates gives us the possibility to reconstruct the topology of the magnetic field at the stellar surface. The method, the planet-host star sample observed so far, and the conclusions obtained from such observations are presented. Fifteen stars with planets have a detected and characterized magnetic field, including the Sun. Although global properties of stars with planets apparently resemble those of stars without known planets, detailed characterization of specific systems has opened a way to probe the energetic environment of exoplanets, with applications on radio emission, habitability, stellar wind/planetary atmosphere interactions, orbital decay, and Ohmic dissipation