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Sagamihara, Japan

Oseki S.,Nagoya University | Oyabu S.,Nagoya University | Ishihara D.,Nagoya University | Enya K.,Japan Aerospace Exploration Agency | And 6 more authors.
Publications of the Astronomical Society of the Pacific | Year: 2015

For future space infrared astronomical coronagraphy, we perform experimental studies on the application of aluminum mirrors to a coronagraph. Cooled reflective optics is required for broadband mid-infrared observations in space, while high-precision optics are required for coronagraphy. For the coronagraph instrument originally proposed for the next-generation infrared astronomical satellite project SPICA (SCI: SPICA Coronagraph Instrument), we fabricated and evaluated the optics consisting of high-precision aluminum off-axis mirrors with diamond-turned surfaces, and conducted a coronagraphic demonstration experiment using the optics with a coronagraph mask. We first measured the wave front errors (WFEs) of the aluminum mirrors with a He–Ne Fizeau interferometer to confirm that the power spectral densities of the WFEs satisfy the SCI requirements. Then we integrated the mirrors into an optical system and evaluated the overall performance of the system. As a result, we estimate the total WFE of the optics to be 33 nm (rms), each mirror contributing 10–20 nm (rms) for the central 14 mm area of the optics, and obtain a contrast of 10-5:4 as a coronagraph in the visible light. At a wavelength of 5 μm, the coronagraphic system is expected to achieve a contrast of ∼10-7 based on our model calculation with the measured optical performance. Thus our experiment demonstrates that aluminum mirror optics is applicable to a highly WFE-sensitive instrument such as a coronagraph in space. © 2015, The Astronomical Society of the Pacific. All rights reserved.

Haze K.,Japan Aerospace Exploration Agency | Enya K.,Japan Aerospace Exploration Agency | Abe L.,University of Nice Sophia Antipolis | Takahashi A.,Japan Aerospace Exploration Agency | And 3 more authors.
Publications of the Astronomical Society of Japan | Year: 2015

We present the fabrication and experimental demonstration of three free-standing binary shaped pupil mask coronagraphs, which are applicable for telescopes with partially obscured pupils. Three masks, designed to be complementary (labeled Mask-A, Mask-B, and Mask-C), were formed in 5 μm thick nickel. The design of Mask-A is based on a one-dimensional barcode mask. The design principle of Mask-B is similar, but has a smaller inner working angle and a lower contrast than Mask-A. Mask-C is based on a concentric ring mask and provides the widest dark region and a symmetric point spread function. Mask-A and Mask-C were both designed to produce a flexibly tailored dark region (i.e., non-uniform contrast). The contrast was evaluated using a light source comprising a broadband super-luminescent light-emitting diode with a center wavelength of 650 nm, and the measurements were carried out in a large vacuum chamber. Active wavefront control was not applied in this work. The coronagraphic images obtained by experiment were mostly consistent with the designs. The contrast of Mask-A within the ranges 3.3-8 λ/D and 8-12 λ/D was ∼ 10-4-10-7 and ∼ 10-7, respectively, where λ is the wavelength and D is the pupil diameter. The contrast of Mask-B was ∼ 10-4 and that of Mask-C over an extended field of view (5-25 λ/D) was ∼ 10-5-10-6. The effect of tilting the masks was investigated, and found to be irrelevant at the ∼ 10-7 contrast level. Therefore the masks can be tilted to avoid ghosting. These high-contrast free-standing masks have the potential to enable coronagraphic imaging over a wide wavelength range using both ground-based and space-borne general-purpose telescopes with pupil structures not specifically designed for coronagraphy. © 2015 The Author. Published by Oxford University Press on behalf of the Astronomical Society of Japan. All rights reserved.

Narita N.,National Institutes of Natural science | Narita N.,Japan National Astronomical Observatory | Narita N.,Graduate University for Advanced Studies | Fukui A.,Japan National Astronomical Observatory | And 12 more authors.
Journal of Astronomical Telescopes, Instruments, and Systems | Year: 2015

We report a development of a multicolor simultaneous camera for the 188-cm telescope at Okayama Astrophysical Observatory in Japan. The instrument, named Muscat (Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets), has a capability of three-color simultaneous imaging in optical wavelengths where CCDs are sensitive. Muscat is equipped with three 1024 × 1024 pixel CCDs which can be controlled independently. The three CCDs detect lights in g′2 (400 to 550 nm), r′2 (550 to 700 nm), and zs,2 (820 to 920 nm) bands using Astrodon Photometrics Generation 2 Sloan filters. The field of view of Muscat is 6.1×6.1 arc min2 with the pixel scale of 0.358 arc sec/pixel. The principal purpose of Muscat is to perform high-precision multicolor transit photometry. For this purpose, Muscat has the capability of self-autoguiding which enables it to fix the positions of stellar images within ∼1 pixel. We demonstrate relative photometric precisions of 0.101%, 0.074%, and 0.076% in g′2, r′2, and zs,2 bands, respectively, for GJ 436 (magnitudes in g′=11.81, r′=10.08, and z′=8.66) with 30-s exposures. The achieved precisions meet our objective, and the instrument is ready for operation. © 2015 The Authors.

Tajitsu A.,Japan National Astronomical Observatory | Aoki W.,Japan National Astronomical Observatory | Yamamuro T.,OptCraft
Publications of the Astronomical Society of Japan | Year: 2012

We report on the design, manufacturing, and performance of the image slicer for the High Dispersion Spectrograph on Subaru Telescope. This instrument is a Bowen-Walraven type image slicer, providing five images of 0″.003 × 1″.005 with a resolving power of R = λ/δλ = 110000. The resulting resolving power and line profiles have been investigated in detail, including estimates of the defocusing effect on the resolving power. The throughput in a wavelength range of from 400 to 700nm is higher than 80%, thereby improving the efficiency of the spectrograph under a seeing condition of 0″.007 by a factor of 1.8. © 2012. Astronomical Society of Japan.

Kambe E.,Japan National Astronomical Observatory | Yoshida M.,Hiroshima University | Izumiura H.,Japan National Astronomical Observatory | Koyano H.,Japan National Astronomical Observatory | And 7 more authors.
Publications of the Astronomical Society of Japan | Year: 2013

We have developed a high-efficiency fiber link (HE mode) connecting Okayama 188-cm telescope to the highresolution spectrograph, HIDES, in order to improve the throughput of the observing system while keeping its radial-velocity measurement precision. In the HE mode, a multi-mode optical fiber collects stellar light within a 2.7-arcsecond diameter field of view (FOV) at the Cassegrain focus, which is twice as large as that of the typical seeing size at our observing site. An image slicer is used at the other end of the link, just in front of the entrance of HIDES, to keep the proper high spectral resolution for such a wide FOV. We have found that the maximum total throughput of the HE mode observations at around 550 nm reaches as high as 9%. Its practical throughput is also found to be more than twice that of the conventional slit observations. We have also confirmed that its reciprocal resolution is over 50000, as designed. The minimum available wavelength, which is determined from an inter-order gap of the echelle spectrum, is about 440 nm, where the gap becomes as narrow as 5 pixels on the CCD detector for the red cross-disperser of HIDES. From measurements of the rms errors of the radial velocity of some stars over one year, the long-term precision is as good as a few ms-1. The fiber modal noise that could degrade the observed spectra may not be significant in the HE mode, as long as the signal-to-noise ratio of a spectrum is lower than 1500. © 2013. Astronomical Society of Japan.

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