arXiv subjects

Shiomi Kumagai

Publications and source records attributed to Shiomi Kumagai.

3 recordsLinked to original sources

arXiv2022

Coronagraph Experiment on Dark-hole Control by Speckle Area Nulling Method

In high-contrast imaging optical systems for direct observation of planets outside our solar system, adaptive optics with an accuracy of lambda/10,000 root mean square is required to reduce the speckle noise down to 1e-10 level in addition to the nulling coronagraph which eliminate the diffracted light. We developed the speckle area nulling (SAN) method as a new dark-hole control algorithm which is capable of controlling speckle electric field in a wide area quickly, in spite of an extension of speckle nulling, and is robust not relying upon an optical model. We conducted a validation experiment for the SAN method with a monochromatic light and succeeded in reducing the intensity of areal speckles by 4.4e-2.

astro-ph.IM↗

arXiv2003

Radioactivity of the Key Isotope 44Ti in SN 1987A

We investigate radioactivity from the decay sequence of 44Ti in a young supernova remnant SN 1987A. We perform Monte-Carlo simulations of degradation of the nuclear lines to explain a late-time bolometric luminosity which is estimated from optical and near-infrared observation at 3600 days after the explosion. Assuming the distance to LMC in between 45.5 and 52.1 kpc, we have obtained the initial 44Ti mass of (0.82-2.3) 10^{-4} solar mass within the current uncertainty of the physical quantities. The resulting fluxes of gamma- and hard X-rays emerged from the 44Ti decay are estimated and compared with the line sensitivity of the INTEGRAL/SPI on board and that of NeXT X-ray satellite planned to be launched in 2010. The effect of 44Ti ionization on the estimated fluxes is briefly remarked.

astro-ph↗

arXiv2003

44Ti radioactivity in young supernova remnants: Cas A and SN 1987A

We investigate radioactivity from the decay sequence of 44Ti in young supernova remnants (SNRs), Cassiopeia A (Cas A) and SN 1987A. It is shown by a linear analysis that ionization of 44Ti, a pure electron capture decay isotope, affects the radioactivity contradistinctively in these two SNRs: Ionization of 44Ti to H-like and He-like states enhances its present radioactivity in Cas A, while such high-ionization decreases its radioactivity in SN 1987A. We briefly discuss the enhancement factor of the present radioactivity of Cas A considering microscopic (atomic/nuclear) physics combined with a hydrodynamical SNR evolution model. For SN 1987A, we have obtained the initial 44Ti mass of (0.82-2.3) X 10^{-4} M_solar from our Monte-Carlo simulations. The resulting fluxes of gamma and hard X-rays emerged from the 44Ti decay are given for the current and future experiments.

astro-ph↗