Sagamihara, Japan
Sagamihara, Japan
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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.

Haze K.,Graduate University for Advanced Studies | Haze K.,Japan Aerospace Exploration Agency | Enya K.,Japan Aerospace Exploration Agency | Abe L.,University of Nice Sophia Antipolis | And 4 more authors.
Publications of the Astronomical Society of Japan | Year: 2011

We conducted a number of multi-color/broadband coronagraph experiments using a vacuum chamber and a binary-shaped pupil mask, which in principle should work at all wavelengths, in the context of the research and development of a stellar coronagraph to observe extra-solar planets (exoplanets) directly. The aim of this work is to demonstrate that subtraction of the Point Spread Function (PSF) and multi-color/broadband experiments using a binary-shaped pupil mask coronagraph would help to improve the contrast in observations of exoplanets. A checkerboard mask, a kind of binary-shaped pupil mask, was used. We improved the temperature stability by installing the coronagraph optics in a vacuum chamber, while controlling the temperature of the optical bench, and covering the vacuum chamber with thermal insulation layers. Active wavefront control was not applied in this work. We evaluated how much the PSF subtraction contributed to the high-contrast observation by subtracting images obtained through the coronagraph. We also carried out multi-color/broadband experiments in order to demonstrate a more realistic observation using Super luminescent Light Emitting Diodes (SLEDs) with center wavelengths of 650 nm, 750 nm, 800 nm, and 850 nm. A contrast of 2.3 × 10-7 was obtained for the raw coronagraphic image and a contrast of 1.3 × 10-9 was achieved after PSF subtraction with a He-Ne laser at 632.8 nm wavelength. Thus, the contrast was improved by around two orders of magnitude from the raw contrast by subtracting the PSF. We achieved contrasts of 3.1 × 10-7, 1.1 × 10-6, 1.6 × 10-6, and 2.5 × 10-6 at the bands of 650 nm, 750 nm, 800 nm, and 850 nm, respectively, in multi-color/broadband experiments. The results show that the contrast within each of the wavelength bands was significantly improved compared with the non-coronagraphic optics. We demonstrated that PSF subtraction is potentially beneficial for improving the contrast of a binary-shaped pupil mask coronagraph; this coronagraph produces a significant improvement in contrast with multi-color/broadband light sources. © 2011. Astronomical Society of 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.

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.

Harakawa H.,Japan National Astronomical Observatory | Sato B.,Tokyo Institute of Technology | Omiya M.,Tokyo Institute of Technology | Fischer D.A.,Yale University | And 12 more authors.
Astrophysical Journal | Year: 2015

We report detections of new exoplanets from a radial-velocity (RV) survey of metal-rich FGK stars by using three telescopes. By optimizing our RV analysis method to long time-baseline observations, we have succeeded in detecting five new Jovian planets around three metal-rich stars, HD 1605, HD 1666, and HD 67087, with masses of 1.3 M⊙, 1.5 M⊙, and 1.4 M⊙, respectively. A K1 subgiant star, HD 1605 hosts two planetary companions with minimum masses of Mp sin i = 0.96MJup and 3.5MJup in circular orbits with the planets periods P = 577.9 and 2111 days, respectively. HD 1605 shows a significant linear trend in RVs. Such a system consisting of Jovian planets in circular orbits has rarely been found and thus HD 1605 should be an important example of a multiplanetary system that is likely unperturbed by planetplanet interactions. HD 1666 is an F7 main-sequence star that hosts an eccentric and massive planet of Mp sin i = 6.4MJup in an orbit with ap = 0.94 AU and eccentricity e = 0.63. Such an eccentric and massive planet can be explained as a result of planetplanet interactions among Jovian planets. While we have found large residuals of rms = 35.6 m s -1, the periodogram analysis does not support any additional periodicities. Finally, HD 67087 hosts two planets of Mp sin i = 3.1MJup and 4.9MJup in orbits with P = 352.2 and 2374 days, and e = 0.17 and 0.76, respectively. Although the current RVs do not lead to accurate determinations of its orbit and mass, HD 67087 c can be one of the most eccentric planets ever discovered in multiple systems. © 2015 The American Astronomical Society. All rights reserved.

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.

Beck P.G.,Catholic University of Leuven | Kambe E.,Okayama Astrophysical Observatory | Hillen M.,Catholic University of Leuven | Corsaro E.,Catholic University of Leuven | And 36 more authors.
Astronomy and Astrophysics | Year: 2015

Context. Red giants are evolved stars that exhibit solar-like oscillations. Although a multitude of stars have been observed with space telescopes, only a handful of red giant stars were targets of spectroscopic asteroseismic observing projects. Aims. We search for solar-like oscillations in the two bright red giant stars γ Psc and θ1 Tau from a time series of ground-based spectroscopy and determine the frequency of the excess of oscillation power νmax and the mean large frequency separation Δν for both stars. Seismic constraints on the stellar mass and radius will provide robust input for stellar modelling. Methods. The radial velocities of γ Psc and θ1 Tau were monitored for 120 and 190 days, respectively. Nearly 9000 spectra were obtained. To reach accurate radial velocities, we used simultaneous thorium-argon and iodine-cell calibration of our optical spectra. In addition to the spectroscopy, we acquired interferometric observations of γ Psc for an independent estimate of the radius. We also analysed 22 days of observations of θ1 Tau with the MOST satellite. Results. The frequency analysis of the radial velocity data of γ Psc revealed an excess of oscillation power around 32 μHz and a large frequency separation of 4.1 ± 0.1 μHz. θ1 Tau exhibits oscillation power around 90 μHz, with a large frequency separation of 6. 9 ± 0.2 μHz. Scaling relations indicate that γ Psc is a star of about 1 M⊙ and 10 R⊙. The object θ1 Tau appears to be a massive star of about 2.7 M⊙ and 10 R⊙. The radial velocities of both stars were found to be modulated on timescales much longer than the oscillation periods. Conclusions. The estimated radii from seismology are in agreement with interferometric observations and also with estimates based on photometric data. While the mass of θ1 Tau is in agreement with results from dynamical parallaxes, we find a lower mass for γ Psc than is found in the literature. The long periodic variability agrees with the expected timescales of rotational modulation. © ESO 2015.

Kotani T.,Japan National Astronomical Observatory | Enya K.,Japan Aerospace Exploration Agency | Nakagawa T.,Japan Aerospace Exploration Agency | Matsuhara H.,Japan Aerospace Exploration Agency | And 36 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

We present the current status of the development of the SPICA Coronagraph Instrument (SCI). SPICA is a nextgeneration 3-meter class infrared telescope, which will be launched in 2022. SCI is high-contrast imaging, spectroscopic instrument mainly for direct detection and spectroscopy of extra-solar planets in the near-to-mid infrared wavelengths to characterize their atmospheres, physical parameters and evolutionary scenarios. SCI is now under the international review process. In this paper, we present a science case of SCI. The main targets of SCI, not only for direct imaging but also for spectroscopy, are young to matured giant planets. We will also show that some of known exoplanets by groundbased direct detection are good targets for SCI, and a number of direct detection planets that are suitable for SCI will be significantly increased in the next decade. Second, a general design of SCI and a key technology including a new highthroughput binary mask coronagraph, will be presented. Furthermore, we will show that SCI is potentially capable of achieving 10-6 contrast by a PSF subtraction method, even with a telescope pointing error. This contrast enhancement will be important to characterize low-mass and cool planets. © 2012 SPIE.

Enya K.,Japan Aerospace Exploration Agency | Abe L.,University of Nice Sophia Antipolis | Takeuchi S.,Japan Aerospace Exploration Agency | Kotani T.,Japan Aerospace Exploration Agency | Yamamuro T.,Optcraft
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

This paper, first, presents introductory reviews of the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission and the SPICA Coronagraph Instrument (SCI). SPICA will realize a 3m class telescope cooled to 6K in orbit. The launch of SPICA is planned to take place in FY2018. The SPICA mission provides us with a unique opportunity to make high dynamic-range observations because of its large telescope aperture, high stability, and the capability for making infrared observations from deep space. The SCI is a high dynamic-range instrument proposed for SPICA. The primary objectives for the SCI are the direct coronagraphic detection and spectroscopy of Jovian exoplanets in the infrared region, while the monitoring of transiting planets is another important target owing to the non-coronagraphic mode of the SCI. Then, recent technical progress and ideas in conceptual studies are presented, which can potentially enhance the performance of the instrument: the designs of an integral 1-dimensional binary-shaped pupil mask coronagraph with general darkness constraints, a concentric ring mask considering the obscured pupil for surveying a wide field, and a spectral disperser for simultaneous wide wavelength coverage, and the first results of tests of the toughness of MEMS deformable mirrors for the rocket launch are introduced, together with a description of a passive wavefront correction mirror using no actuator. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

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