The recent improvement in observational instruments enables us to observe forming planets embedded in protoplanetary disks. In particular, direct-imaging observation of Hydrogen line emission is crucial to diagnose gas accretion, which is a late stage of gaseous planet formation. To analyze the observed hydrogen lines from forming planets, we numerically modeled the hot gas heated by the shock due to the accretion flow onto the planetary surface. This model converts the observed hydrogen line luminosity into the mass accretion rate of the forming planet.
Besides the line luminosity, our model predicts the spectral profile of the hydrogen lines. In addition, the detection of multiple lines leads to a more detailed analysis. However, so far, forming planets are detected only at a single line of Hα and only in low-resolution spectroscopy or band observation because the brighter central star makes the planet observation harder. On the other hand, wide-orbit (>~100AU) objects are less affected by the central star and are targets of high-resolution spectroscopy and/or high-sensitivity observation of hydrogen lines. Independent of the formation history, our hydrogen line emission model is applicable to the planetary-mass objects including such wide-orbit planetary-mass objects. In fact, some of the wide-orbit objects are in the planetary mass regime, and multiple hydrogen lines and their mid- or high-resolution spectra have been already detected.
In this poster, we demonstrate how our model constrains the formation of planetary-mass objects from their hydrogen line emission. This work not only diagnoses the formation of wide-orbit planetary-mass objects but also is a milestone for future observation of more detailed observations of forming planets.