Photo-ionization of planetary winds: case study HD209458b

TL;DR

This study uses 3D hydrodynamic simulations with radiation transfer to model the ionization and Ly-alpha absorption of hot Jupiter HD 209458b, successfully matching observed spectral features and exploring effects of stellar flux and mass loss.

Contribution

It introduces detailed 3D hydrodynamic models with radiation transfer for planetary winds, improving understanding of Ly-alpha absorption in hot Jupiters.

Findings

Hydrodynamic interaction and photoionization calculations reproduce observed Ly-alpha features.

Ionizing stellar flux has an almost linear effect on absorption in the planetary wake.

Model variations match the 10% absorption at -100 km/s observed in HD 209458b.

Abstract

Close-in hot Jupiters are exposed to a tremendous photon flux that ionizes the neutral escaping material from the planet leaving an observable imprint that makes them an interesting laboratory for testing theoretical models. In this work we present 3D hydrodynamic simulations with radiation transfer calculations of a close-in exoplanet in a blow-off state. We calculate the Ly-$\alpha$ absorption and compare it with observations of HD 209458b an previous simplified model results.Our results show that the hydrodynamic interaction together with a proper calculation of the photoionization proccess are able to reproduce the main features of the observed Ly-$\alpha$ absorption, in particular at the blue-shifted wings of the line. We found that the ionizing stellar flux produce an almost linear effect on the amount of absorption in the wake. Varying the planetary mass loss rate and the radiation flux, we were able to reproduce the $10\%$ absorption observed at $-100~\mathrm{km~s^{-1}}$.