Keiichi Maeda

Dust grains play a crucial role on formation and evolution history of stars and galaxies in the early universe. We investigate the formation of dust grains in the ejecta of population III supernovae including pair–instability supernovae which are expected to occur in the early universe, applying a theory of non–steady state nucleation and grain growth. Dust formation calculations are performed for core collapse supernovae with the progenitor mass Mpr ranging from 13 to 30 M ⊙ and for pair–instability supernovae with Mpr = 170 and 200 M⊙. In the calculations, the time evolution of gas temperature in the ejecta, which strongly affects the number density and size of newly formed grains, is calculated by solving the radiative transfer equation taking account of the energy deposition of radio active elements. Two extreme cases are considered for the elemental composition in the ejecta; unmixed and uniformly mixed cases within the He–core, and formation of CO and SiO molecules is assumed to be complete. The results of calculations for core collapse supernovae and pair–instability

Photometric and spectroscopic data of the energetic Type Ic supernova (SN) 2002ap are presented, and the properties of the SN are investigated through models of its spectral evolution and its light curve. The SN is spectroscopically similar to the hypernova SN 1997ef. However, its kinetic energy [~(4-10) ? 1051 ergs] and the mass ejected (2.5-5 M?) are smaller, resulting in a faster evolving light curve. The SN synthesized ~0.07 M? of 56Ni, and its peak luminosity was similar to that of normal SNe. Brightness alone should not be used to define a hypernova, whose defining character, namely very broad spectral features, is the result of high kinetic energy. The likely main-sequence mass of the progenitor star was 20-25 M?, which is also lower than that of both hypernovae SN 1997ef and SN 1998bw. SN 2002ap appears to lie at the low-energy and low-mass end of the hypernova sequence as it is known so far. Observations of the nebular spectrum, which is expected to dominate by the summer of 2002, are necessary to confirm these values.