高橋 葵

Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (P(or)b) of 12.76 days. The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous P-orb from TESS data. We confirmed the transit signal and P-orb using ground-based photometry with MuSCAT2 and MuSCAT3, and validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host star is inactive, with an X-ray-to-bolometric luminosity ratio of log L-X/L-bol approximate to - 5.7. Joint analysis of the light curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 +/- 0.05 R-circle plus, a 3 sigma mass upper limit of 3.9M(circle plus), and an equilibrium temperature of 315 +/- 6 K assuming zero albedo. The transmission spectroscopy metric (TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.

The Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE) is a planned M-class science space mission by the Institute of Space and Astronautical Science, the Japan Aerospace Exploration Agency. JASMINE has two main science goals. One is Galactic archaeology with a Galactic Center survey, which aims to reveal the Milky Way's central core structure and formation history from Gaia-level (similar to 25 ${\mu} $as) astrometry in the near-infrared (NIR) Hw band (1.0-1.6 ${\mu} $m). The other is an exoplanet survey, which aims to discover transiting Earth-like exoplanets in the habitable zone from NIR time-series photometry of M dwarfs when the Galactic Center is not accessible. We introduce the mission, review many science objectives, and present the instrument concept. JASMINE will be the first dedicated NIR astrometry space mission and provide precise astrometric information on the stars in the Galactic Center, taking advantage of the significantly lower extinction in the NIR. The precise astrometry is obtained by taking many short-exposure images. Hence, the JASMINE Galactic Center survey data will be valuable for studies of exoplanet transits, asteroseismology, variable stars, and microlensing studies, including discovery of (intermediate-mass) black holes. We highlight a swath of such potential science, and also describe synergies with other missions.

Measuring the absolute brightness of the zodiacal light (ZL), which is the sunlight scattered by interplanetary dust particles, is important not only for understanding the physical properties of the dust but also for constraining the extragalactic background light (EBL) by subtracting the ZL foreground. We describe the results of high-resolution spectroscopic observations of the night sky in the wavelength range of 300-900 nm with the double spectrograph on the Hale telescope to determine the absolute brightness of the ZL continuum spectra from the Fraunhofer absorption line intensities. The observed fields are part of the fields observed by the Spitzer Space Telescope for the EBL study. Assuming that the spectral shape of the zodiacal light is identical to the solar spectrum in a narrow region around the Fraunhofer lines, we decomposed the observed sky brightness into multiple emission components by amplitude parameter fitting with spectral templates of the airglow, ZL, diffuse Galactic light, integrated starlight, and other isotropic components including EBL. As a result, the ZL component with the Ca ii lambda lambda 393.3, 396.8 nm Fraunhofer lines around 400 nm is clearly separated from the others in all fields with uncertainties around 20%, mainly due to the template errors and the time variability of the airglow. The observed ZL brightness in most of the observed fields is consistent with the modeled ZL brightness calculated by combining the most conventional ZL model at 1250 nm based on the Diffuse Infrared Background Experiment and the observational ZL template spectrum based on the Hubble Space Telescope. However, the ecliptic plane observation is considerably fainter than the ZL model, and this discrepancy is discussed in terms of the optical properties of the interplanetary dust accreted in the ecliptic plane.

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 similar to 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 developed a new germanium reflective echelle grating fabricated by Canon Inc. for HISPEC (The High-Resolution Infrared Spectrograph for Exoplanet Characterization) for the Keck telescope. We employed germanium as a substrate, an ideal material to achieve small wavefront error (WFE) and high diffraction efficiencies close to the theoretical limit, with robust wavefront stability against temperature change. Furthermore, we developed a grating with an apex angle of less than 90 degrees to enhance the diffraction efficiency of both polarization states. We report that the full-size gratings with 80-degree apex angles show very high diffraction efficiencies, 95% of the theoretical limit, and very small WFE (similar to 13 nm). In addition, we present WFE measurements of a small prototype germanium echelle grating under cryogenic conditions, and we confirmed that the WFE of the diffracted beam is almost identical at room temperature and at 84 K.

The High-Resolution Infrared Spectrograph for Exoplanet Characterization (HISPEC) is a new instrument for the W. M. Keck Observatory that enables R similar to 100,000 spectroscopy simultaneously across the y, J, H, and K astronomical bands (0.98-2.5 mu m). The fiber delivery subsystem of HISPEC is responsible for routing science and calibration light throughout the observatory efficiently. It consists of high-performance single mode fibers, a photonic lantern, mechanical and MEMS-based fiber switchers that allow for the reconfiguration of light paths. To efficiently cover this large wavelength range, a silica fiber is used for the y&J bands and the 1x3 photonic lantern while a ZBLAN fiber is used for the H&K bands. The HK fiber is a custom design by Le Verre Fluore. The fibers route the science light from the focal point of the adaptive optics system to spectrographs in the basement similar to 65 m away, hence, the fibers must be very efficient. To calibrate the instrument, several mechanical fiber switchers can be used to direct calibration light to the spectrograph or the front of the optical train. Some switchers must make over 800 cycles annually, while maintaining sub-3% coupling losses between fibers with core sizes of 4.4 mu m. To achieve this, extensive testing was conducted, in which throughput and dust accumulation were monitored to determine how these parameters are impacted by switch preparation procedures and ambient environmental conditions. We developed systems to automatically and remotely clean and image fiber end faces in situ. We have created a protocol that allows us to achieve thousands of switch connections reliably. Additionally, through the 25,000+ switch cycles ran during testing, we identified shortcomings in the design of these mechanical fiber switchers which will be remedied for the final instrument. In this paper, we describe the detailed design of the fiber delivery subsystem for HISPEC and outline several innovative solutions and summarize our de-risking activities to date.

Structural, Thermal and Optical Performance (STOP) analysis is performed to investigate the stability of the telescope to be onboard the Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE). In order to perform one of the prime science objectives, high-precision astrometric observations in the wavelength range of 1.0-1.6 mu m toward the Galactic center to reveal its central core structure and formation history, the JASMINE telescope is requested to be highly stable with an orbital change in the image distortion pattern being less than a few 10 mu as after low-order correction. The JASMINE telescope tried to satisfy this requirement by adopting two design concepts. Firstly, the mirror and their support structures are made of extremely low coefficient-of-thermal-expansion materials. Secondly, their temperatures are highly stabilized with an orbital variation of less the 0.1 degrees C by the unique thermal control idea. Through the preliminary STOP analysis, the structural and thermal structural feasibility of the JASMINE telescope is considered. By combining the results of the structural and thermal design, its thermal deformation is estimated. The optical performance of the JASMINE telescope after the thermal deformation is numerically evaluated. It is found that the thermal displacement of the mirrors in the current structural thermal design produces a slightly large focus-length change. As far as the focus adjustment is adequately applied, the orbital variation of the image distortion pattern is suggested to become acceptable after the low-order correction.

We describe scientific objective and project status of an a stronomical 6U CubeSat mission VERTECS (Visible Extragalactic background RadiaTion Exploration by CubeSat). The scientific goal of VERTECS is to reveal the star-formation history along the evolution of the universe by measuring the extragalactic background light (EBL) in the visible wavelength. Earlier observations have shown that the near-infrared EBL is several times brighter than integrated light of individual galaxies. As candidates for the excess light, first-generation stars in the early universe or low-redshift intra-halo light have been proposed. Since these objects are expected to show different emission spectra in visible wavelengths, multi-color visible observations are crucial to reveal the origin of the excess light. Since detection sensitivity of the EBL depends on the product of the telescope aperture and the field of view, it is possible to observe it with a small but wide-field telescope system that can be mounted on the limited volume of CubeSat. In VERTECS mission, we develop a 6U CubeSat equipped with a 3U-sized telescope optimized for observation of the visible EBL. The bus system composed of onboard computer, electric power system, communication subsystem, and structure is based on heritage of series of CubeSats developed at Kyushu Institute of Technology in combination with high-precision attitude control subsystem and deployable solar array paddle required for the mission. The VERTECS mission was selected for JAXA-Small Satellite Rush Program (JAXA-SMASH Program), a new program that encourages universities, private companies and JAXA to collaborate to realize small satellite missions utilizing commercial small launch opportunities, and to diversify transportation services in Japan. We started the satellite development in December 2022 and plan to launch the satellite in FY2025.

The extragalactic background light (EBL) is the integrated emission from all objects outside of the Milky Way galaxy and is a crucial observational quantity in the broader study of the history of cosmic structures. In the nearinfrared EBL, there have been measurements of an emission component several times brighter than the cumulative light from extragalactic galaxies. This unknown radiation component has led to proposals for candidate source objects, such as first stars and galactic halo brown dwarfs. These source objects exhibit distinct radiation spectra in the visible wavelength. The VERTECS (Visible Extragalactic background RadiaTion Exploration by CubeSat) project is focused on continuously observing the visible EBL using a wide-field small telescope on a 6U CubeSat. The primary characteristic of this telescope is its high-throughput (S Omega > 10(-6) m(2)sr). The 3U-sized optical telescope onboard this satellite consists of a lens optics with a total field of view of 6 degrees x 6 degrees, pixel field of view of 11" x 11", a highly sensitive and low-noise detector module, and a baffle to eliminate stray light from the Sun and Earth. Additionally, color filters divide the wavelength range from 400 to 800 nm into four bands. Our observation strategy involves capturing 60-second exposure images while shifting the observed field by 3 degrees increments and stacking the acquired images to perform photometry in the four bands. Thus far, most of the telescope design has met the required specifications, and the project is currently advancing towards the production of an engineering model. This project was selected in the JAXA-SMASH and is currently progressing in satellite development with a planned launch in the 2025 fiscal year. In this presentation, we will report on the strategy for observing the visible EBL, the progress in the development of the optical telescope, and the future plans.

The extragalactic background light (EBL) is the integrated diffuse emissions from unresolved stars, galaxies, and intergalactic matter along the line of sight. The EBL is regarded as consisting of stellar emissions and thus an important observational quantity for studying global star formation history throughout cosmic time. Intensity and anisotropy in the near-infrared EBL as measured by the Cosmic Infrared Background ExpeRiment (CIBER), NASA's sounding rocket experiment, and previous infrared satellites exceed the predicted signal from galaxy clustering alone. The objective of CIBER-2 is to unveil the EBL excess by observing it at extended wavelengths into the visible spectrum with an accuracy better than CIBER. The onboard instrument of CIBER2 comprises a 28.5-cm telescope cooled to 90K, and three HAWAII-2RG detectors coupled with dual-band filters for photometric mapping observations in six wavebands simultaneously and with linear variable filters for low-resolution spectroscopy. Although CIBER-2 made a successful first flight from White Sands Missile Range in New Mexico in 2021, technical problems such as contamination of thermal radiation from the rocket chassis and degradation of the mirror coat were recognized. Despite a successful second flight in 2023 solving the problems with the revised onboard instrument, the experiment was aborted because of trouble with the rocket tracking system. In this paper, we describe the parachute-recovered payload rebuilt after the second flight and the testing, and we report the successful flight on May 5th 2024.

Extragalactic Background Light (EBL), the cumulative light from outside the galaxy, is a crucial observational target for understanding the history of the universe. We are developing a CubeSat; VERTECS (Visible Extragalactic background RadiaTion Exploration by CubeSat) with a 6U size (approximately 10 x 20 x 30 cm), equipped with Solar Array Wings (SAW). Our mission is to conduct extensive observations of the visible EBL. The satellite is designed to operate in a sun-synchronous orbit at an altitude of 500-680 km (approximately 15 orbits per day) and observe the EBL on the shadow side to avoid stray light from the Sun and Earth. To observe EBL, a high-performance CMOS sensor, attitude control devices, and high-speed communication equipment X-band are essential. We should note that these components these components consume a significant amount of power. Therefore, some strategic operational plans are necessary to operate this CubeSat within the limited power resources. In addition, VERTECS needs to meet its mission requirements, conducting 10 observations, 4 data downlinks, and 1 command uplink within a day. We have constructed some operational scenarios utilizing attitude control and SAW to meet these requirements, and we also constructed a power budget simulation for VERTECS. In this presentation, we describe how we plan to operate VERTECS utilizing the subsystems and the results of the power simulation during the operation.

We report on the discovery of an Earth-sized transiting planet (R ( p ) = 1.015 +/- 0.051 R (circle plus)) in a P = 4.02 day orbit around K2-415 (EPIC 211414619), an M5V star at 22 pc. The planet candidate was first identified by analyzing the light-curve data obtained by the K2 mission, and it is here shown to exist in the most recent data from TESS. Combining the light curves with the data secured by our follow-up observations, including high-resolution imaging and near-infrared spectroscopy with IRD, we rule out false-positive scenarios, finding a low false-positive probability of 2 x 10(-4). Based on IRD's radial velocities of K2-415, which were sparsely taken over three years, we obtain a planet mass of 3.0 +/- 2.7 M (circle plus) (M ( p ) < 7.5 M (circle plus) at 95% confidence) for K2-415b. Being one of the lowest-mass stars (approximate to 0.16 M (circle dot)) known to host an Earth-sized transiting planet, K2-415 will be an interesting target for further follow-up observations, including additional radial velocity monitoring and transit spectroscopy.

<jats:title>Abstract</jats:title> <jats:p>We report the near-infrared radial velocity (RV) discovery of a super-Earth planet on a 10.77 d orbit around the M4.5 dwarf Ross 508 (Jmag = 9.1). Using precision RVs from the Subaru Telescope IRD (InfraRed Doppler) instrument, we derive a semi-amplitude of $3.92^{+0.60}_{-0.58}\:\mbox{m}\:{\mbox{s}^{-1 } }$, corresponding to a planet with a minimum mass $m \sin i = 4.00^{+0.53}_{-0.55}\, M_{\oplus }$. We find no evidence of significant signals at the detected period in spectroscopic stellar activity indicators or MEarth photometry. The planet, Ross 508 b, has a semi-major axis of $0.05366^{+0.00056}_{-0.00049}\:$au. This gives an orbit-averaged insolation of ≈1.4 times the Earth’s value, placing Ross 508 b near the inner edge of its star’s habitable zone. We have explored the possibility that the planet has a high eccentricity and its host is accompanied by an additional unconfirmed companion on a wide orbit. Our discovery demonstrates that the near-infrared RV search can play a crucial role in finding a low-mass planet around cool M dwarfs like Ross 508.</jats:p>

We report the first measurement of the zodiacal light (ZL) polarization spectrum in the near-infrared between 0.8 and 1.8 mu m. Using the low-resolution spectrometer on board the Cosmic Infrared Background Experiment, calibrated for absolute spectrophotometry and spectropolarimetry, we acquire long-slit polarization spectral images of the total diffuse sky brightness toward five fields. To extract the ZL spectrum, we subtract the contribution of other diffuse radiation, such as the diffuse galactic light, the integrated starlight, and the extragalactic background light. The measured ZL polarization spectrum shows little wavelength dependence in the near-infrared, and the degree of polarization clearly varies as a function of the ecliptic coordinates and solar elongation. Among the observed fields, the North Ecliptic Pole shows the maximum degree of polarization of similar to 20%, which is consistent with an earlier observation from the Diffuse Infrared Background Experiment on board on the Cosmic Background Explorer. The measured degree of polarization and its solar elongation dependence are reproduced by an empirical scattering model in the visible band and also by a Mie scattering model for large absorptive particles, while a Rayleigh scattering model is ruled out. All of our results suggest that the interplanetary dust is dominated by large particles.

Interplanetary dust (IPD) is thought to be recently supplied from asteroids and comets. Grain properties of the IPD can give us information about the environment in the protosolar system, and can be traced from the shapes of silicate features around 10 mu m seen in the zodiacal emission spectra. We analyzed mid-infrared slit-spectroscopic data of the zodiacal emission in various sky directions obtained with the Infrared Camera on board the Japanese AKARI satellite. After we subtracted the contamination due to instrumental artifacts, we successfully obtained high signal-to-noise spectra and have determined detailed shapes of excess emission features in the 9-12 mu m range in all sky directions. According to a comparison between the feature shapes averaged over all directions and the absorption coefficients of candidate minerals, the IPD was found to typically include small silicate crystals, especially enstatite grains. We also found variations in the feature shapes and the related grain properties among the different sky directions. From investigations of the correlation between feature shapes and the brightness contributions from dust bands, the IPD in dust bands seems to have a size frequency distribution biased toward large grains and shows indications of hydrated minerals. The spectra at higher ecliptic latitudes showed a stronger excess, which indicates an increase in the fraction of small grains included in the line of sight at higher ecliptic latitudes. If we focus on the dependence of detailed feature shapes on ecliptic latitudes, the IPD at higher ecliptic latitudes was found to have a lower olivine/(olivine + pyroxene) ratio for small amorphous grains. The variation of the mineral composition of the IPD in different sky directions may imply different properties of the IPD from different types of parent bodies, because the spatial distribution of the IPD depends on the type of the parent body.

The Mid-infrared Imager, Spectrometer, Coronagraph (MISC) is one of the instruments studied both for the Origins Space Telescope (OST) Mission Concept 1 and 2. The highest ever spectro-photometric stability achieved by MISC transit spectrometer module (MISC TRA) enables to detect bio-signatures (e.g., ozone, water, and methane) in habitable worlds in both primary and secondary transits of exoplanets and makes the OST a powerful tool to bring a revolutionary progress in exoplanet sciences. Combined with the spectroscopic capability in the FIR provided by other OST instruments, the MISC widens the wavelength coverage of OST down to 4 mu m, which makes the OST a powerful tool to diagnose the physical and chemical condition of the ISM using dust features, molecules lines and atomic and ionic lines. The MISC also provides the OST with a focal plane guiding function for the other OST science instruments as well as its own use.