Contributed Talk - Splinter Exoplanets

Thursday, 14 September 2023, 14:15   (H 3007)

Accreting gas giants: Low H alpha emission efficiency

Gabriel-Dominique Marleau, Yuhiko Aoyama, William Béthune, Rolf Kuiper, Christoph Mordasini
Universität Duisburg

Surveys have looked for H alpha emission from accreting gas giants but found very few objects. Analyses of the detections and non-detections have assumed that the entire gas flow feeding the planet is in radial free-fall. However, hydrodynamical simulations suggest that this is far from reality. We calculate the H alpha emission from multidimensional accretion onto gas giants, following the gas flow from Hill-sphere scales down to the circumplanetary disc (CPD) and the planetary surface. We use radiation-hydrodynamics simulations and do not smooth the gravitational potential. We find that most of the gas falls at too large a distance on the CPD to generate H alpha. The corresponding H alpha production efficiency is orders of magnitude smaller than usually assumed, which must be taken into account when analysing (non-)detection statistics. We discuss observational prospects, including other hydrogen lines.