ABSTRACT: Advancements in observational technology have opened new windows for studying exoplanets, especially those in the early stage of formation. Notably, some of these newly forming exoplanets exhibit self-luminous hydrogen lines. These emissions arise from gas heated to tens of thousands of Kelvin, contradicting their photospheric temperature of a few thousand Kelvin. Such discrepancies suggest that these planetary hydrogen lines are indicative of dynamic accretion processes; gas accretion releases its gravitational energy and heats the gas hot enough to emit hydrogen lines. Consequently, these hydrogen lines serve as a valuable probe into the underlying mechanisms of planet formation.

In this presentation, I will explore the insights offered by hydrogen line observations. By modeling the accretion shock on the planetary surface and the resulting hydrogen line emissions, we can interpret the flux of these lines as indicative of the mass accretion rate. Additionally, the spectral profiles and simultaneous observations of multiple hydrogen lines can reveal further details, such as the accretion geometry and extinction effects due to the surrounding environment. Lastly, I will discuss upcoming observational instruments and the insights they are expected to provide.

BIO: Dr. Aoyama's research focuses on planet formation, particularly the formation of giant planets. He studied at the University of Tokyo and received his bachelor's degree in 2014, master's in 2016, and Ph.D. in 2019. After his doctoral studies, Dr. Aoyama joined the Institute for Advanced Study at Tsinghua University as a postdoctoral researcher until 2022. Then, he moved to the Kavli Institute for Astronomy and Astrophysics at Peking University in 2022, where he currently continues his postdoctoral research.