Magnetospheres of hot Jupiters: hydrodynamic models and UV absorption
Exoplanetary systems: past, present, and future
Richard Alexander
Graham Wynn (University of Leicester), Hastyar Mohammed (University of Leicester), Jonathan Nichols (University of Leicester), Barbara Ercolano (Excellence Cluster Universe, Garching)
University of Leicester
We present hydrodynamic simulations of stellar wind-magnetosphere interactions in hot Jupiters such as WASP-12b. For fiducial stellar wind rates we find that a planetary magnetic field of a few Gauss produces a large magnetospheric cavity, typically 6-9 planetary radii in size. A bow shock forms ahead of the magnetosphere, but the pre-shock gas is only mildly supersonic so the shock is invariably weak. This results in a characteristic signature in the ultraviolet light curve: a broad absorption feature that leads the optical transit by 10-20% in orbital phase. The shapes of our synthetic light curves are consistent with existing observations of WASP-12b, but the required near-UV optical depth can only be achieved if the shocked gas cools rapidly, and we further show that radiative cooling is inefficient. We therefore conclude that a magnetospheric bow shock is unlikely to be responsible for the observed near-UV absorption in the WASP-12 system, and suggest that future UV observations other hot Jupiters will provide a straightforward test to distinguish between different models of circumplanetary absorption.


16:30 - 18:00
EX - LT3 (320)