In this study , we have applied our planetary accretion shock model ( Aoyama et al . 2018 ) to the two accreting proto - gas giants - PDS 70 b and c , for which Hα emission fluxes and profiles were very recently observed ( Wagner et al . 2018;Haffert et al . 2019 ) . We have demonstrated that the new observational data , namely , spectral profiles , combined with Hα luminosity , help us to narrow down the possible ranges of preshock velocity and number density . As a result , better constraints on mass accretion rate and protoplanet mass gives rise to deeper insight into late - stage accretion onto gas giants .