The South Africa Near-infrared Doppler instrument (SAND) is a time-stable high-dispersion spectrograph, covering the z- and Y-bands simultaneously (849 - 1085 nm) with the maximum spectral resolution of ∼60,000. We aim to monitor the radial velocity of M-dwarfs with the precision of a few m/s level, which enables us to search for habitable exoplanets. Our another scientific motivation is the statistical investigation of young planets and stellar atmosphere to comprehensively understand the formation senario of stellar systems. We are planning to install the SAND to telescopes at the South African Astronomical Observatory (SAAO) in Sutherland, since the Southern sky covers plentiful stellar associations with young stars. The SAND is a fiber-fed spectrograph, and we can change telescope used to collect the star light by switching the fiber connection. It will be operated mainly with two telescopes: the Prime-focus Infrared Microlensing Experience telescope (PRIME) and the InfraRed Survey Facility (IRSF), which both are managed by universities in Japan. This strategy of using multiple telescopes gives us opportunities of frequent and long-term observations, which provides well phase coverage in radial velocity monitoring and results in non-bias search for exoplanets. Most of the components used in the spectrograph and the fiber injection module have been fabricated. We will present the detailed status and recent progress: designing the fiber injection module and the thermal control system, examination of fiber characteristics, and estimating our target candidates.
We present the current status of our development of a new near-infrared spectrometer for the InfraRed Survey Facility (IRSF) 1.4-m telescope, located in South Africa. The spectrometer is designed to cover the wavelength range of 1.0–1.6 μm with the spectral resolution of 550 at 1.2 μm and 730 at 1.6 μm and have a small number of optical surfaces to achieve a high optical throughput of 55%. The spectrometer is also equipped with a near-infrared slit viewer with a 3′×4′ field of view to perform precise spectral monitoring and mapping. We have tentatively completed the development of the instrument by using a commercial InGaAs detector and confirmed its expected sensitivity and spectral resolution by test observations with the Kagoshima University 1-m telescope. We now plan to replace the current detector with a new InGaAs detector developed for astronomical observations. The new detector covers the same wavelength range as the current one but has a significantly lower dark current and a larger array format, which enables us to upgrade the spectrometer to have higher sensitivity and spectral resolution. We plan to mount the spectrometer on the IRSF telescope by early 2025 after the detector is replaced and the second test observation with the Kagoshima University telescope is done.
SMI (SPICA Mid-infrared Instrument) is one of the three focal-plane science instruments for SPICA. SMI is the Japanese-led instrument proposed and managed by a university consortium. SMI covers the wavelength range from 10 to 36 μm with four separate channels: the low-resolution (R = 60 – 160) spectroscopy function for 17 – 36 μm, the broad-band (R = 5) imaging function at 34 μm, the mid-resolution (R = 1400 – 2600) spectroscopy function for 18 – 36 μm, and the high-resolution (R = 29000) spectroscopy function for 10 – 18 μm. In this presentation, we will show the latest design and specifications of SMI as a result of feasibility studies.
We measured the transmittance of low-resistivity (∼ 10^2 Ωcm) and high-resistivity (> 10^10 Ωcm) CdZnTe, which are candidates for Immersion grating (IG) in 10–18μm wavelength, at cryogenic temperature. IG is a compact diffraction grating and we are developing a cryogenically operated 10--18μm IG for SMI/HR (SPICA Mid-Infrared Instrument / High-Resolution spectrometer) of SPICA (SPace Infrared telescope for Cosmology and Astrophysics) We performed two experiments: transmittance measurement with a convergent light Fourier transform spectrometer, and with a collimated lamp beam system. Our result shows that the low-resistivity CdZnTe has large absorption (> 0.5 cm^{−1} ) and the high-resistivity CdZnTe has low absorption (< 0.1 cm^{-1} ) at 8.5K at 10--18 μm. The high-resistivity CdZnTe is promising as an IG material although higher precision measurement is needed to determine whether it meets the absorption coefficient requirement (< 0.01 cm^{-1}) at cryogenic temperature.
SMI (SPICA Mid-infrared Instrument) is one of the two focal-plane science instruments for SPICA. SMI is the Japanese led instrument proposed and managed by a nation-wide university consortium in Japan and planned to be developed in collaboration with Taiwan and the US. SMI covers the wavelength range from 12 to 36 μm with 4 separate channels: the low-resolution (R = 50-120) spectroscopy function for 17-36 μm, the broad-band (R = 5) imaging function at 34 μm, the mid-resolution (R = 1300-2300) spectroscopy function for 18-36 μm, and the high-resolution (R = 28000) spectroscopy function for 12-18 μm. In this paper, we show the results of our conceptual design and feasibility studies of SMI.
Focal Plane Arrays (FPA) are key items for modern astronomical observations in the near infrared wavelength, but it is very expensive and not easy to get them. Less expensive NIR FPAs with reasonable performance are very important to spread NIR observation extensively. FPA640×512 manufactured by Chunghwa Leading Photonics Tech is a 640×512 InGaAs detector covering the 0.9-1.7 μm wavelength. Since this array is significantly cheaper than the commonly used NIR FPAs in the astronomical observation, it is possible to be a good choice for particular projects which do not need many pixels, if FPA640×512 has acceptable performance for the purpose. We have evaluated one test grade array of FPA640×512 both in the room and low temperature environment. In order to evaluate the characteristics of this FPA in the low temperature environment, we cooled it down by the mechanical refrigerator and confirmed that it works at 100 K. We have found that the dark current reduces exponentially as the FPA temperature decreases, but it hits the bottom at~1000 e−/sec bellow 200 K with the default setting. We are trying to reduce the dark current by optimizing the bias voltage and the current to the MUX circuit. The latest experiments have shown the possibility that the dark current decreases to~200 e−/sec. This value is still higher than that of NIR FPAs used in the scientific observation, but it may be applicable for the particular purpose, for example, FPAs for slit viewer in spectrometers, wave front sensor, and so on.
Owing to its high specific stiffness and high thermal stability, silicon carbide is one of the materials most suitable for large space-borne optics. Technologies for accurate optical measurements of large optics in the vacuum or cryogenic conditions are also indispensable. Within the framework of the large SiC mirror study program led by JAXA, we manufactured an 800-mm-diameter lightweight telescope, all of which is made of HB-Cesic, a new type of carbon-fiber-reinforced silicon carbide (C/SiC) material developed jointly by ECM, Germany and MELCO, Japan. We first fabricated an 800-mm HB-Cesic primary mirror, and measured the cryogenic deformation of the mirror mounted on an HB-Cesic optical bench in a liquid-helium chamber. We observed the cryo-deformation of 110 nm RMS at 18 K with neither appreciable distortion associated with the mirror support nor significant residual deformation after cooling. We then integrated the primary mirror and a high-order aspheric secondary mirror into a telescope. To evaluate its optical performance, we established a measurement system, which consists of an interferometer in a pressure vessel mounted on a 5-axis adjustable stage, a 900-mm auto-collimating flat mirror, and a flat mirror stand with mechanisms of 2-axis tilt adjustment and rotation with respect to the telescope optical axis. We installed the telescope with the measurement system into the JAXA 6-m chamber and tested them at a vacuum pressure to verify that the system has a sufficiently high tolerance against vibrations in the chamber environment. Finally we conducted a preliminary study of sub-aperture stitching interferometry, which is needed for telescopes of our target missions in this study, by replacing the 900-mm flat mirror with a rotating 300-mm flat mirror.
We present our new optical and near-infrared (NIR) spectrometer for the IRSF 1.4m telescope. The concept
of it is an effective use of photons, and so we have designed it to obtain a spectrum of the 0.4-2.5μm range
simultaneously and have a small number of optical surfaces in order to reduce reflection loss. Light collected by
the telescope is separated into optical (0.45-0.90μm) and NIR (1.0-2.5μm) wavelengths by a dichroic entrance
window, and two spectrometers are prepared, one for the optical wavelengths and another for the NIR. We use a
sapphire prism in the NIR spectrometer, and a diffraction grating in the optical spectrometer. The optical design
is very simple and the number of optical surfaces is 9 for optical and 10 for NIR (not including the telescope
mirrors). A 1024×250 pixels CCD (optical) and a 1024×1024 HgCdTe detector array (NIR) are used. The
spectral resolution will be 470@0.70μm and 380@1.8μm with a 1” slit width. A NIR slit viewer with a 3’.5 ×
3’.5 field of view is also mounted. The development of the spectrometer will be complete by March 2013.
SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a Japan-led infrared astronomical satellite project
with a 3.2-m lightweight cryogenic telescope. The SPICA telescope has stringent requirements such as that for the
imaging performance to be diffraction-limited at the shortest core wavelength of 5 microns at the operating temperature
of 6 K. The design of the telescope system has been studied by the Europe-Japan telescope working group led by ESA
with the European industries, the results of which will be presented in other papers. We here present our recent optical
testing activities in Japan for the SPICA telescope, focusing on the experimental and numerical studies of stitching
interferometry. The full pupil of the SPICA telescope will be covered by a sub-pupil array consisting of small
autocollimating flat mirrors (ACFs), which are rotated with respect to the optical axis of the telescope. For preliminary
stitching experiments, we have fabricated an 800-mm lightweight telescope all made of the C/SiC called HBCesic, which
is a candidate mirror material for the SPICA telescope, and started optical testing with 900-mm and 300-mm ACFs at an
ambient temperature. ACFs can suffer significant surface deformation in testing a telescope at cryogenic temperatures,
which is difficult to be measured directly. We therefore investigate the effects of the surface figure errors of the ACFs on
stitching results by numerical simulation.
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