| Project/Area Number |
17340051
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Astronomy
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| Research Institution | Hokkaido University |
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Principal Investigator |
BABA Naoshi Hokkaido University, Grad. School of Eng., Professor (70143261)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIGAKI Tsuyoshi Asahikawa Natl., College of Technology, Assoc. Prof. (40312384)
TAMURA Motohide Natl. Astronomical Obs., Opt. IR Div., Assoc. Prof. (00260018)
MIURA Noriaki Kitami Inst. Technology, Fac. Eng., Professor (30209720)
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| Project Period (FY) |
2005 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥11,800,000 (Direct Cost: ¥10,900,000、Indirect Cost: ¥900,000)
Fiscal Year 2007: ¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000)
Fiscal Year 2006: ¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 2005: ¥5,100,000 (Direct Cost: ¥5,100,000)
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| Keywords | Extrasolar planet / Stellar coronagraph / Polarization / Nulling interference / High-spatial resolution / 系外惑星 / スペックル雑音 / 偏光干渉 / 差分法 |
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| Research Abstract |
We conducted several optical simulation experiments for detecting directly exoplanets and observing their spectra. Our method is based on the polarization differential stellar coronagraph that has been proposed by Baba and Murakami. Starlight is generally considered to be unpolarized. On the other hand the light from its planet is expected to be partially polarized, because the planetary light is the scattered and reflected one by the parent starlight. When we observe a star-planet system with mutually orthogonal polarized light and take the difference of these two images, the unpolarized component is cancelled out and the partially polarized component remains. This is the principle of the polarization differential method.
However, the simple polarization differentiation does not always produce good results. Therefore, we have proposed to conduct the analysis of the degree of polarization for image and objective spectra. Here, the degree of polarization means a value of the difference between two orthogonally linear polarizations normalized by the intensity at the point. We can discriminate planetary light from noisy starlight.
In our optical simulation we set the degree of polarization of a planet model to 50%. An angular distance between a star model and its planet model is set to 4.8λ/D, where λ is the central wavelength for observation and D a diameter of a telescope. An intensity ratio of the planet model to the star model is 1.1x10^<-5>. In the polarization differential image we could not discriminate the planetary image from speckle noise, but we could clearly identify the planetary image from the representation of the degree of polarization.
We also conducted the experiment to obtain objective spectra of exoplanets. Our experimental results show that the analysis of the polarization degree is also very useful to distinguish planetary spectrum from noisy stellar spectra.
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