談話会
Colloquium

Kei Tanaka (UC Boulder)
Massive Star Formation across Cosmic History
Massive stars play essential roles in a wide range of astrophysical settings throughout cosmic history, and thus it is crucial to understand how they form. Compared to low-mass star formation, research on massive star formation has been dramatically developing in recent years. The strong radiative feedback from massive protostars had been considered so powerful that it could determine the stellar upper mass limit. However, our model calculations and ALMA observations suggest that, unlike the conventional picture, the disk accretion can overcome strong radiative feedback even in the formation of very massive stars (>50-100Msun), similar to the standard low-mass star formation. Furthermore, we extend the theoretical frameworks and the observational projects to lower metallicity environments in order to connect the present-day and the early universes.

Kenta Hotokezaka (U. Tokyo)
Late-time emission of neutron star mergers
The intensive observations of the electromagnetic counterpart of GW170817 successfully revealed the nature of the merger outflows. Here I'll talk about the theoretical aspects of kilonova and afterglow emission at later times. The observations of the late-time kilonova (nebular emission) and afterglow emissions are particularly useful to study the atoms synthesized in merger and the geometrical structure of the relativistic outflow, respectively. I'll also discuss the role of radioactivity in kilonova ejecta such as the energy deposition and ionization.