Abstract:
Recent improvements in observational instruments and techniques enable us to observe the forming planets directly. Particularly, the detection of hydrogen lines is expected to be a clue to understanding the gas accretion process onto the protoplanets. The hydrogen line excess due to gas accretion is well known and has been studied in the context of accreting protostars. As the simplest way to interpret the planetary hydrogen lines, some previous studies assumed that the emission mechanism is similar for protostars and protoplanets. The accreting gas reaches the highest temperature when it hits on the object's sruface and passes the strong shock. However, on the accreting protostars, the shock-heated gas is too hot to emit hydrogen lines. The hydrogen lines mainly come from a warm pre-shock gas, instead. In contrast, the shock-heated gas on the protoplanets has an appropriate temperature to emit hydrogen lines. The emission mechanism of hydrogen lines can be qualitatively different for accreting protostars and protoplanets. In this talk, I will discuss the difference between hydrogen lines from protostars and protoplanets.
