Gas-giant planets have a large mass and strong gravity, so they significantly affect the planetary system and its formation. Since they are mainly composed of hydrogen gas, how and when gas accretes to the gas-giants are important not only for the planets themselves but also for their planetary system. Recently, some young gas giants are observed with the direct-imaging method. In particular, an atomic hydrogen line, Hα, is expected to be a clue to the gas-giant formation. Hydrogen lines, which excited hydrogens emit, infers gas is hot (>10^4 K) enough to excite atomic hydrogen (~10 eV). One of the hydrogen lines, Hα, is detected in some protoplanetary disks, where planets are thought to form. The Hα energy source is thought to be the gravitational-energy release of the gas accreting towards gas-giants. So, Hα observation is expected to constrain how the gas accretes. In this study, we constructed a numerical model of shock-heated gas associated with the gas accretion towards gas-giants. From the model results, we aim to constrain the properties of accreting gas-giants. As a demonstration, by using the observed Hα luminosity and profile, we constrained planetary mass and mass accretion rate of proto-gas-giants, PDS70b and c.
