http://arxiv.org/abs/1908.03510
Strong atmospheric escape has been detected in several close-in exoplanets. As these planets are mostly made of hydrogen, observations in hydrogen lines, such as Ly-alpha and H-alpha lines, are powerful diagnostics of escape. Here, we simulate the evolution of atmospheric escape of close-in giant planets and calculate their associated Ly-alpha and H-alpha transits. For that, we use a 1D hydrodynamic escape model to compute the physical properties of the escaping atmosphere and a ray tracing technique to simulate the spectroscopic transits. We consider giant planets with masses 0.3 and 1M_jup, orbiting at 0.045au. The host star is assumed to be of solar type, evolving from 10 to 5000 Myr. We find that younger giants show higher rates of atmospheric escape, owing to a favourable combination of higher irradiation fluxes and weaker gravities. The less massive planet shows even higher escape rates (10^{10} – 10^{13} g/s) than the more massive one (10^9 – 10^{12} g/s) over their evolution. We estimate that the 1-M_jup planet would lose at most 1% of its initial mass due to escape, while the 0.3-M_jup planet, could lose up to 20% of its mass. These results give support to the idea that the Neptunian desert has been formed due to significant mass loss in low-gravity planets. We also computed spectroscopic transits in Ly-alpha and H-alpha lines. At younger ages, we find that the mid-transit Ly-alpha line is saturated at line centre, while H-alpha transits produce transit depths of at most 3 – 4% in excess of their geometric transit. While at older ages, Ly-alpha absorption is still significant (and could even be saturated in the case of the lower mass planet), the H-alpha absorption nearly disappears. This is because the extended atmosphere of neutral hydrogen becomes almost entirely in the ground state after ~1.2 Gyr.
A. Allan and A. Vidotto
Mon, 12 Aug 19
32/42
Comments: N/A