DIX Planetary Science Seminar

The metastable Helium (He∗) lines near 10830 ̊A are ideal probes of atmospheric erosion–a common phenomenon of close-in exoplanet evolution. A handful of exoplanet observations yielded well-resolved He∗ absorption features in transits, yet they were mostly analyzed with 1D isothermal models prescribing mass-loss rates. We present a 3-D hydrodynamic model with ray-tracing radiative transfer and non-equilibrium thermochemsitry. Starting from the observed stellar/planetary properties with reasonable assumptions about the host's high energy irradiation, we predict from first principle the mass loss rate, the temperature and ionization profiles, and 3D outflow kinematics. Our simulations well reproduced the observed He∗ line profiles and light curves of WASP-69b and WASP-107b two of the best observed systems. In addition, we investigated how photo evaporative mass loss depends on host star spectral types, XUV flux levels, stellar flares, stellar wind strength etc. We also discuss variability introduced to shear instability and the synergy between He* and Lyman-alpha observations in constraining.