The dichotomy of atmospheric escape in AU Mic b

STEPHEN CAROLAN; ALINE VIDOTTO; PETER PLAVCHAN; CAROLINA VILLARREAL D'ANGELO; GOPAL HAZRA

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2020

0035-8711

Here, we study the dichotomy of the escaping atmosphere of the newly discovered close-in exoplanet AU Microscopii (AU Mic) b. On one hand, the high extreme-ultraviolet stellar flux is expected to cause a strong atmospheric escape in AU Mic b. On the other hand, the wind of this young star is believed to be very strong, which could reduce or even inhibit the planet´s atmospheric escape. AU Mic is thought to have a wind mass-loss rate that is up to 1000 times larger than the solar wind mass-loss rate. To investigate this dichotomy, we perform 3D hydrodynamics simulations of the stellar wind-planetary atmosphere interactions in the AU Mic system and predict the synthetic Ly alpha  transits of AU Mic b. We systematically vary the stellar wind mass-loss rate from a ´no wind´ scenario to up to a stellar wind with a mass-loss rate of 1000 Mdot_sun. We find that, as the stellar wind becomes stronger, the planetary evaporation rate decreases from 6.5 × 1010 g s-1 to half this value. With a stronger stellar wind, the atmosphere is forced to occupy a smaller volume, affecting transit signatures. Our predicted Ly alpha absorption drops from ~20 per cent in the case of ´no wind´ to barely any Ly alpha absorption in the extreme stellar wind scenario. Future Ly alpha transits could therefore place constraints not only on the evaporation rate of AU Mic b, but also on the mass-loss rate of its host star.