GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is one of the three candidates of ISAS/JAXA’s Strategic L-class mission for the 2030s. The 1.2 m aperture, 50 K cryogenic space telescope with the wide-field camera (WFC) will provide the 1,260 square arcmin field-of-view for five photometric bands between 2 and 8 μm. The high resolution spectrometer (HRS) will observe the 10–18 µm with a wavelength resolution of 30,000. The GREX-PLUS WFC field-of-view is 130 times larger than that of the James Webb Space Telescope and similar to those of Euclid and Roman Space Telescope. Since these two survey missions are limited to the wavelength less than around 2 µm, GREX-PLUS will extend the wavelength coverage beyond 2 μm, providing versatile legacy imaging survey significantly improved from previous Spitzer imaging survey in the same wavelength range. The spectral resolution of the GREX-PLUS HRS is 10 times higher than that of the James Webb Space Telescope, opening a new window of the mid-infrared high-resolution spectroscopy from space. The main scientific themes are the galaxy formation and evolution and the planetary system formation and evolution. The GREX-PLUS WFC aims to detect the first generation of “bright” galaxies at redshift z > 15. The GREX-PLUS HRS aims to resolve the Kepler motion of water vapor molecules and identify the location of the water “snowline” in ∼ 100 proto-planetary disks. Both instruments will provide unique data sets for a broad range of scientific topics including galaxy mass assembly, origin of super massive blackholes, infrared background radiation, molecular spectroscopy in the interstellar medium, transit spectroscopy for exoplanet atmosphere, planetary atmosphere in the Solar system, and so on. This paper presents the status of the concept design of GREX-PLUS, including telescope system, WFC, HRS, cooling system, and spacecraft bus system.
Ultraviolet (UV) spectroscopy is one of the most powerful tools used in a wide range of scientific fields from planetary science to astronomy. We propose a future UV space telescope, LAPYUTA (Life-environmentology, Astronomy, and PlanetarY Ultraviolet Telescope Assembly), selected as a candidate for JAXA’s 6th M-class mission in 2023. Launch is planned for the early 2030s. LAPYUTA will accomplish the following four objectives related to two scientific goals: understanding (1) the habitable environment and (2) the origin of structure and matter in the universe. Objective 1 focuses on the subsurface ocean environments of Jupiter's icy moons and the atmospheric evolution of terrestrial planets. Objective 2 characterizes the atmosphere of the exoplanets around the habitable zone and estimates their surface environment by detecting their exospheric atmosphere. In cosmology and astronomy, Objective 3 tests whether the structures of presentday galaxies contain ubiquitous Ly-α halos and reveals the physical origins of Ly-α halos. Objective 4 elucidates the synthesis process of heavy elements based on observations of ultraviolet radiation from hot gas immediately after neutronstar mergers. LAPYUTA will perform spectroscopic and imaging observations in the far-UV range of 110-190 nm with an effective area of >300 cm2 and a high spatial resolution of 0.1 arcsec. The apogee is 2,000 km, and the perigee is 1,000 km to avoid the influence of the geocorona when observing oxygen and hydrogen atoms and the Earth's radiation belt.
In this paper, we present our approach regarding the compensation of defective pixels in the infrared array detector used in the NINJA spectrograph for the Subaru Telescope. While it is typical to use a detector with minimal defective pixels for infrared spectrographs, our HAWAII-2RG detector has a central area with a defective pixel rate of 10%. Therefore, we compensate for defective pixels by mechanically shifting the detector along the focal plane in the direction of dispersion. This approach applies the concept of dithering in imaging observation to a spectrograph, and the shifting mechanism is designed to have a maximum movement distance of 8 mm. We present the expected performance of the compensation and the actual mechanical structure fabricated.
Near-INfrared and optical Joint spectrograph with Adaptive optics (NINJA) is an optical to near-infrared (NIR) spectrograph optimized for the laser tomography adaptive optics (LTAO) system at the Subaru telescope, realized by the adaptive secondary mirror and four-laser guide star (LGS) system now under development. One of the primary science objectives of this spectrograph is wide-band spectroscopic follow-up of transient sources like GRB, supernovae, or gravitational wave sources down to 22 mag in the J -band. NINJA consists of two spectrograph units, one is in the optical (0.35-0.85 µm) and the other in the NIR (0.85-2.5 µm), and a fore-optics which splits the light from the telescope to the spectrographs and wavefront sensors (WFSs) of LTAO. Each spectrograph has a slit with 0.35′′ wide and 5′′ long, and a spectral resolution of R=3000-4000 utilizing a grating. The four LGSs are planned to be arranged on a circle around the slit with a radius of about 8′′, and a patrol field of view (FoV) of a tip-tilt guide star is about 2′ diameter. With two dichroic mirrors, the fore-optics splits the light of the FoV into three wavelength ranges of 0.35-0.85 µm, 0.85-2.5 µm, and 0.589 µm for LGS. In this paper, we report the overall system of NINJA and a conceptual design of the optics.
GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is a new mission concept for ISAS/JAXA’s strategic L-class mission program in the 2030s. With a 1.2 m aperture, a 50 K cryogenic space telescope will have a < 1, 400 arcmin2 wide-field camera with 6 bands in the 2–10 μm wavelength range and a high-dispersion spectrometer with a wavelength resolution of < 30, 000 in the 10–18 μm band. The cryogenic infrared mission concept of GREX-PLUS is based on SPICA, exploiting the technical resources so far studied and developed, such as an active cooling system. The high-dispersion spectrometer of GREX-PLUS is based on the high-dispersion channel of the SPICA Mid-Infrared Instrument (SMI). The wide-field camera of GREX-PLUS is also based on previous concept studies for the ISAS/JAXA’s WISH mission concept. GREX-PLUS is a concept proposal for a Japan-led mission but international collaborations are also welcome.
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