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Keigo Enya 한국천문학회 2017 天文學論叢 Vol.32 No.1
This paper reviews the legacy of the SPCIA Coronagraph Instrument(SCI) of which the primary scientific objective is the characterizationof Jovian exoplanets by coronagraphic spectroscopy in the infrared. Studies on binary shaped pupil mask coronagraphs are described. Cryogenic active optics is discussed as another key technology. Then approaches to observing habitable zones in exoplanetary systemswith a passively-cooled space infrared telescope are discussed. The SCI was dropped in a drastic change of the SPICA mission. However, its legacy is useful for space-borne infrared telescopesdedicated for use in exoplanetary science in the future,especially for studies of biomarkers.
WIDEBAND SPECTRAL DISPERSER MADE OF ZnS FOR EXOPLANET CHARACTERIZATION USING SPACE-BORNE TELESCOPES
Keigo Enya,Naofumi Fujishiro 한국천문학회 2017 天文學論叢 Vol.32 No.1
We present the developmentof a spectral dispersion devicefor wideband spectroscopy for which the primary scientificobjective is the characterization of transiting exoplanets. The principle of the disperser is simple: a grating isfabricated on the surface of a prism. The direction of the spectral dispersion power of the prismis crossed with the grating. Thus, the prism separates the spectrum into individualorders while the grating produces a spectrum for each order. In this work, ZnS was selected as the materialfor the cross disperser, which was designed to coverthe wavelength region, λ = 0.6 -13 μm,with a spectral resolving power, R ≥ 50. A disperser was fabricated, and an evaluationof its surface was conducted. Two spectrometer designs, one adopting ZnS(λ = 0.6 -13 μm, R ≥ 300)and the other adopting CdZnTe( λ = 1 -23 μm, R ≥ 250), are presented. The spectrometers, each of which has no moving mechanical parts,consist simply of a disperser, a focusing mirror, and a detector.
LABORATORY EXPERIMENTS OF OFF-AXIS MIRROR OPTICS OF ALUMINUM FOR SPACE INFRARED MISSIONS
Shinji Oseki,SHINKI OYABU,DAISUKE ISHIHARA,Keigo Enya,Kanae Haze,Takayuki Kotani,HIDEHIRO KANEDA,Miho Nishiyama,Lyu Abe,Tomoyasu Yamamuro 한국천문학회 2017 天文學論叢 Vol.32 No.1
We report our research on aluminum mirror optics for future infrared astronomical satellites. For space infrared missions, cooling the whole instrument is crucial to suppress the infrared background and detector noise. In this aspect, aluminum is appropriate for cryogenic optics, because the same material can be used for the whole structure of the instrument including optical components thanks to its excellent machinability, which helps to mitigate optical misalignment at low temperatures. We have fabricated aluminum mirrors with ultra-precision machining and measured the wave front errors (WFEs) of the mirrors with a Fizeau interferometer. Based on the power spectral densities of the WFEs, we confirmed that the surface accuracy of all the mirrors satisfied the requirements for the SPICA Coronagraph Instrument. We then integrated the mirrors into an optical system, and examined the image quality of the system with an optical laser. As a result, the total WFE is estimated to be 33 nm (rms) from the Strehl ratio. This is consistent with the WFEs estimated from the measurement of the individual mirrors.