2019ApJ...885...94T

Advances in high-resolution imaging have revealed Hα emission separate from the host star. It is generally believed that the emission is associated with planets forming in protoplanetary disks. However, the nature of this emission is still not fully understood. Here we report a modeling of Hα emission from the planets around the young star PDS 70. Using standard magnetospheric accretion models previously applied to accreting young stars, we find that the observed line fluxes can be reproduced using a range of parameters relevant to PDS 70b and c, with a mean mass accretion rate of log({dot}M) = -8.0 ± 0.6 M_Jup yr^–1 and -8.1 ± 0.6 M_Jup yr^–1 for PDS 70b and PDS 70c, respectively. Our results suggest that Hα emission from young planets can originate in the magnetospheric accretion of mass from the circumplanetary disk. We find that empirical relationships between mass accretion rate and Hα line properties frequently used in T Tauri stars are not applicable in the planetary mass regime. In particular, the correlations between line flux and mass accretion rate underpredict the accretion rate by about an order of magnitude, and the width at the 10% height of the line is insensitive to the accretion rate at {dot}M < 10^–8 M_Jup yr^–1.