Division of Theoretical Astronomy, National Astronomical Observatory of Japan

Research Highlights

Probing the Stellar Explosions with Presolar Grains


Presolar grains, discovered in meteorites, are tiny solid particles that are considered to have been produced before the formation of Solar System. A few particles of presolar Al2O3 grains with sizes above 0.5 um are believed to have been originated in the ejecta of core-collapse supernovae (SNe).

With the aim of clarifying the formation condition of such large Al2O3 grains, we investigate the condensation of Al2O3 grains for wide ranges of the gas density and cooling rate. We find that the formation of submicron-sized Al2O3 grains requires at least 10 times higher gas densities than those presented by one-dimensional SN models. This indicates that presolar Al2O3 grains might be formed in dense gas clumps and that the measured sizes of presolar grains can be a powerful tool for constraining the physical conditions of SN ejecta.

The figure plots the calculated average radius of newly formed Al2O3 grains as a function of number density of Al atoms (red line). The hatched region depicts the expected ranges of the Al density in the ejecta, referring to a one-dimensional model of a Type II-P SN (Kozasa et al. 2009). The dashed vertical line denotes the minimum Al density necessary for explaining the measured sizes (radius of 0.25 um) of presolar Al2O3 grains.

Probing the Physical Condition of Supernova Ejecta with the Measured Sizes of Presolar Al2O3 Grains, by Takaya Nozawa, Shigeru Wakita, Yasuhiro Hasegawa, Takashi Kozasa, 2015, ApJ Letters, 811, L39 (5pp)
[ADS] [arXiv]
Takaya Nozawa [personal website]

All sky simulations of gravitational lensing

One of our simulated gravitational lensing maps. The red regions represent high surface mass density regions, while the blue regions correspond to underdens regions in the Universe.

Gravitational lensing is one of the most promising tools to probe matter density distribution in the Universe. The foreground gravitational field causes small image distortion of distant galaxies. The small distortion contains, collectively, rich cosmological information about the matter distribution. We can reconstruct the foreground mass distribution from observed image of distant galaxies with statistical analysis. Ongoing/upcoming imaging surveys such as Hyper Suprime-Cam (HSC) survey in the near future, will provide the largest dark matter map we have never seen before. Therefore, it is important and timely to investigate the cosmological information content of the reconstructed mass map. In order to realize the realistic situation in galaxy imaging surveys, we perform gravitational lensing simulations on curved full-sky as shown in the figure. We then utilize these simulations to create two hundreds of mock weak lensing catalogs with the proposed sky coverage in ongoing HSC survey. These mock catalogs enable us to study the statistical property of reconstructed mass map from gravitational lensing obserables. The detailed comparison with our simulation results and theoretical model of large scale structure is found in the text.
Probing cosmology with weak lensing selected clusters – I. Halo approach and all-sky simulations , Monthly Notices of the Royal Astronomical Society, 453, 3043-3067 [ADS]
Masato Shirasaki



3rd DTA Symposium:
The Origins of Planetary Systems: from the Current View to New Horizons

2015 June 1 (Mon) - June 4 (Thu)
NAOJ Mitaka, Large seminar room
webpage: http://th.nao.ac.jp/meeting/dta2015a_planet/