Modeling the radio signature of the orbital parameters, rotation and magentic field of exoplanets

Sebastien Hess
LOFAR TKP Meeting, Amsterdam, June 2011

Transcript

1. Exoplanet observation with LOFAR, What do we expect ? Sébastien Hess1 Philippe Zarka2 1LATMOS – University of Versailles-St Quentin, France 2Observatoire de Paris, France
2. Acceleration of electrons in the magnetosphere  aurorae + radio emissions [Lamy et al.,2010] [Lamy et al.,2008]
3. [Zarka,2001] The same phenomenon is expected for exoplanets. Hot Jupiters should have powerful emissions. These emissions could be observable from the ground. Hot Jupiters ?
4. • Auroral radio emissions are generated through the Cyclotron Maser Instability. • Resonance of a circularely polarized wave with the gyration of the electrons at the cyclotron frequency. The polarization depends on the magnetic hemisphere • Emission frequency close to the cyclotron frequency, proportionnal to the magnetic field. The observed frequency tells the strength of the exoplanet magnetic field ! The emissions are modulated by the magnetic field Modulation with the exoplanet's rotation period ! What do these emissions looks like ?
5. What does the auroral emissions look like ? Example of the Jupiter's emissions. • The main radio emissions of Jupiter are due to its interaction with Io. • Short interaction => sources localized in longitude • Radio emissions appear as arcs in the time-frequency plane
6. • Anisotropy of the beaming pattern causes the arc shape. • Can be modeled, with physical assumption on the beaming angle. • Online tool : ExPRES (Exoplanetary and Planetary Radio Emission Simulator). • We can model observation of exoplanetary radio emissions to derive physical parameters of the emitting exoplanet.
7. Io-Jupiter analogous : Star radio emission triggered by the exoplanet Intensity Polarization Revolution period Gives information on star's Rotation rate and magnetic field
8. Earth magnetosphere Saturn magnetosphere Interaction = convection due to the solar wind flow long duration (hours) and large scale (in longitude) Modulated with the planet period Interaction= combination of the solar wind flow and the corotation of the plasma. Most intense on the morning side, but modulated by the planet period Sub-corotating radio arcs are also observed [Lamy et al.,2008]
9. Revolution period Mag. moment Type of interaction Emission at all longitudes Emission in a sector of local time (Earth like) (Saturn like) Revolution period
10. Revolution period Mag. moment Type of interaction Emission at all longitudes Corotating emissions (Earth like) (Saturn and Jupiter like) Revolution period Rotation period
11. Orbit inclination Revolution period Mag. moment Intensity Polarization Type of interaction Polarization depends on the emitting hemisphere (RH for north, LH for south) North South
12. Rotation period Dipole tilt / offset Intensity Polarization Orbit inclination Revolution period Type of interaction Mag. moment
13. Conclusion : If we are able to detect radio emissions from exoplanet, we could derive : • The revolution period of the planet • The inclination of the exoplanet's orbit (Hence, the mass of the exoplanet) • The rotation period of the exoplanet (Only way to obtain it for gazeous planets) • The magnetic field of the planet (at least the dipole component) • Information about how the planet and its star interact. Published in : S. Hess, P. Zarka, Modeling of the radio signature of the exoplanets orbital parameters, Astronomy and Astrophysics, 2011
14. Next step : DETECTING THEM !