ENERGETIC NEUTRAL ATOMS AROUND HD 209458b: ESTIMATIONS OF MAGNETOSPHERIC PROPERTIES

Abstract

HD 209458b is an exoplanet found to transit the disk of its parent star. Observations have revealed a large population of high-velocity atomic hydrogen around the "hot Jupiter" HD 209458b during transit. This work expands on an earlier work studying the production of energetic neutral atoms (ENAs) as a result of the interaction between the stellar wind and the exosphere. We present an improved flow model that, together with stellar wind values similar to the ones in our solar system, further supports that the observed hot hydrogen are ENAs. We also study how the production of ENAs depends on the exospheric parameters, and establish an upper limit for the obstacle standoff distance at approximately 4-10 planetary radii. Finally we compare the results obtained for the obstacle standoff distance with existing exomagnetospheric models, and show how the magnetic moment of HD 209458b can be estimated from ENA observations for different exospheric scenarios.