臼井 文彦

Abstract 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 (∼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.

Abstract We have conducted numerical simulations to reproduce the observed optical energy profile of the 15 October 2021 (UT) impact flash on Jupiter, which was the largest and the most well-observed flash event detected by ground-based movie observations. The observed long-duration (∼5.5 s) optical emission can be reproduced by an impact of an object with an exceptionally small angle of entry relative to the horizontal. The apparent lack of the impact debris feature despite the large impact object was possibly due to the shallower angle of entry (≤12○), which resulted in the lower ablation per unit volume at altitudes higher than 50 km, and the volume densities of the ablated materials were too low to allow the debris particulates to coagulate. The absence of temporal methane absorption change in the observed flash spectrum is consistent with the best-fit results. The model better fits the observed optical energy profile for weaker material (cometary and stony) cases than for metallic ones. Based on the simulation results, prospects for future observations of impact flashes are discussed.

Most C-complex asteroids have albedo values less than 0.1, but there are some high-albedo (bright) C-complex asteroids with albedo values exceeding 0.1. To reveal the nature and origin of bright C-complex asteroids, we conducted spectroscopic observations of the asteroids at visible and near-infrared wavelengths. As a result, the bright B-, C-, and Ch-type (Bus) asteroids, which are subclasses of the Bus C-complex, are classified as DeMeo C-type asteroids with concave curvature, B-, Xn-, and K-type asteroids. Analogue meteorites and material (CV/CK chondrites, enstatite chondrites/achondrites, and salts) associated with these spectral types of asteroids are thought to be composed of minerals and material exposed to high temperatures. A comparison of the results obtained in this study with the SDSS photometric data suggests that salts may have occurred in the parent bodies of 24 Themis and 10 Hygiea, as well as 2 Pallas. The bright C-complex asteroids in other C-complex families were likely caused by impact heating. Bright C-complex asteroids that do not belong to any families are likely to be impact-metamorphosed carbonaceous chondrites, CV/CK chondrites, or enstatite chondrites/achondrites....

Kuiper belt objects (KBOs) are thought to be remnants of the early Solar System, and their size distribution provides an opportunity to explore the formation and evolution of the outer Solar System<SUP>1-5</SUP>. In particular, the size distribution of kilometre-sized (radius = 1-10 km) KBOs represents a signature of initial planetesimal sizes when planets form<SUP>5</SUP>. These kilometre-sized KBOs are extremely faint, and it is impossible to detect them directly. Instead, the monitoring of stellar occultation events is one possible way to discover these small KBOs<SUP>6-9</SUP>. However, until now, there has been no observational evidence for occultation events of KBOs with radii of 1-10 km. Here, we report the first detection of a single occultation event candidate by a KBO with a radius of 1.3 km, which was simultaneously provided by two low-cost small telescopes coupled with commercial complementary metal-oxide-semiconductor cameras. From this detection, we conclude that the surface number density of KBOs with radii exceeding 1.2 km is 6 × 10<SUP>5</SUP> deg<SUP>-2</SUP>. This surface number density favours a theoretical size distribution model with an excess signature at a radius of 1-2 km (ref. <SUP>5</SUP>). If this is a true KBO detection, this implies that planetesimals before their runaway growth phase grew into kilometre-sized objects in the primordial outer Solar System and remain as a major population in the present-day Kuiper belt....

Sample return from the near-Earth asteroid known as 25143 Itokawa was conducted as part of the Hayabusa mission, with a large number of scientific findings being derived from the returned samples. Following the Hayabusa mission, Hayabusa2 was planned, targeting sample return from a primitive asteroid. The primary target body of Hayabusa2 was asteroid 162173 Ryugu; however, it was also necessary to gather physical information for backup target selection. Therefore, we examined five asteroids spectroscopically, 43 asteroids spectrophotometrically, and 41 asteroids through periodic analysis. Hence, the physical properties of 74 near-Earth asteroids were obtained, which helped the Hayabusa2 backup target search, and also furthered understanding of the physical properties of individual asteroids and their origins....

Context. Deep mid-infrared (MIR) surveys have revealed numerous strongly star-forming galaxies at redshift z ≲ 2. Their MIR fluxes are produced by a combination of continuum and polycyclic aromatic hydrocarbon (PAH) emission features. The PAH features can dominate the total MIR flux, but are difficult to measure without spectroscopy. <BR /> Aims: We aim to study star-forming galaxies by using a blind spectroscopic survey at MIR wavelengths to understand evolution of their star formation rate (SFR) and specific SFR (SFR per stellar mass) up to z ≃ 0.5, by paying particular attention to their PAH properties. <BR /> Methods: We conducted a low-resolution (R ≃ 50) slitless spectroscopic survey at 5-13 μm of 9 μm flux-selected sources (>0.3 mJy) around the north ecliptic pole with the infrared camera (IRC) onboard AKARI. After removing 11 AGN candidates by using the IRC photometry, we identify 48 PAH galaxies with PAH 6.2, 7.7, and 8.6 μm features at z < 0.5. The rest-frame optical-MIR spectral energy distributions (SEDs) based on CFHT and IRC imaging covering 0.37-18 μm were produced, and analysed in conjunction with the PAH spectroscopy. We defined the PAH enhancement by using the luminosity ratio of the 7.7 μm PAH feature over the 3.5 μm stellar component of the SEDs. <BR /> Results: The rest-frame SEDs of all PAH galaxies have a universal shape with stellar and 7.7 μm bumps, except that the PAH enhancement significantly varies as a function of the PAH luminosities. We identify a PAH-enhanced population at z ≳ 0.35, whose SEDs and luminosities are typical of luminous infrared galaxies. They show particularly larger PAH enhancement at high luminosity, implying that they are vigorous star-forming galaxies with elevated specific SFR. Our composite starburst model that combines a very young and optically very thick starburst with a very old population can successfully reproduce most of their SED characteristics, although we cannot confirm this optically think component from our spectral analysis....

We performed the data reduction of the AKARI Phase 3 near-infrared spectroscopy (2-5.5 micrometers with prism) of the LMC, which covers almost the same regions as in Phase 1&2 (in the order of 10 deg(exp 2)). A new spectroscopic catalog which includes approximately 350 contamination free (approximately 200 new) sources and approximately 1200 not heavily contaminated (approximately 700 new) sources is created. The time intervals between Phase 1&2 observations and the corresponding Phase 3 observations are more than 200 days, allowing us to analyze the spectroscopic variabilities of YSOs and carbon stars. In this paper, we report the details of the current version of the Phase 3 spectroscopic catalog as well as some of the results so far obtained....

AKARI performed about 10,000 spectroscopic observations with the Infrared Camera (IRC). These IRC observations provide unique spectral data at near- and mid-infrared wavelengths. These data enable astronomical research in the various fields throughout the next few decades, empowered by its high sensitivity and unique wavelength coverage. Near-infrared spectral data taken with the point source aperture mask (1' x 1' aperture, called the ''Np'' window) are provided. The spectral coverage is 2.5-5.0 micrometers in the grism mode, and 1.8-5.5 micrometers in the prism mode. Subpixel stacking of spectral images, cosmic ray removal, revised distortion correction, revised estimation of uncertainty of the flux density, and wavelength calibration considering the refractive index of the grism are taken into account in the data processing, producing the first version of the spectral catalogue released in April 2016. Remaining issues, including revised spectral calibration by subtracting the second-order light and re-examination of the flux uncertainty, are now implemented in the latest data reduction process. The revised catalogue based on the data reduction with the latest version toolkit will be delivered soon....

Here we briefly overview the latest data reduction toolkit and reduced images with it that are already available online. AKARI performed approximately 4000 pointed observations over 16 months in Phases 1 and 2, when the telescope and instruments were cooled by liquid helium. Observation targets include solar system objects, Galactic objects, local galaxies, and galaxies at cosmological distances. We describe major updates on calibration processes of near- and mid-infrared images taken by the InfraRed Camera, which has nine photometric filters covering 2-27 micrometers continuously. The latest toolkit has been applied to data from each pointed observation to generate calibrated and stacked images. About 90% of the stacked images have a position accuracy better than 1.5 arcsec. Uncertainties in aperture photometry estimated from a typical standard sky deviation of stacked images are a factor of approximately 2-4 smaller than those of AllWISE at similar wavelengths. This work has already been published as Egusa et al. (2016)....

A good absolute photomertic calibration is essential to achieve science goals in astronomical observations. In the imaging observations with the Infrared Camera (hereafter IRC) aboard AKARI, standard stars near the North Ecliptic Pole region (NEP), the South Ecliptic Pole region (SEP), and in the Large Magellanic Cloud (LMC) are used for the calibration (Tanabe et al. 2008). The IRC imaging toolkit was updated in 2015, thus the calibration values need to be revised accordingly. In the present work, using the updated IRC imaging toolkit, we derived the conversion factors from the measured values in analog-to-digital unit (ADU) to the absolute flux densities by comparing the observed and estimated brightness of a set of standard stars. In addition, we reexamined the aperture correction factors for the point sources in the IRC imaging observations. We found that these correction factors are consistent with those derived in Tanabe et al. (2008) within 10%....

We present details of a point source catalogue using all the reference images for spectroscopic observations of AKARI/IRC-S9W (Yamagishi et al. in this volume). The catalogue includes about 42,000 sources, for which we performed PSF fitting with two-dimensional Gaussian and cross-identifications with 2MASS and WISE PSCs. About 80% of the sources in the catalogue are found in the other PSCs. Thanks to the deeper sensitivity and higher spatial resolution than WISE, we find 8400 sources and provide 9 micrometers flux for 8500 objects not detected in WISE W3. The procedure of this work can be applied to all the pointed imaging data of IRC, which shall detect a few tens thousands MIR sources and be helpful to understand the SED of many objects such as YSO....

The property of interplanetary dust (IPD), which has been recently emitted from planetesimals like asteroids and/or comets, can give us the information about the environment where asteroids and comets were formed during the planet-formation stage. These can include clues of any planetesimal scattering due to planets' migration. We use silicate features around 10 micrometers as a tracer of the thermal history. In this study, we analyze mid-infrared spectroscopic data of zodiacal emission at 74 different directions obtained with AKARI/IRC. After we examined and subtracted instrumental artifacts, we successfully obtained the high S/N spectra and detected the silicate feature in all pointing data. They also suggest the variations in dust temperature and shape of the feature among different ecliptic latitudes....

The AKARI all sky surveys provide us unique and independent infrared datasets of classical and recurrent novae taken with two photometric bands at 9 micrometers (S9W) and 18 micrometers (L18W) of the Infrared Camera (IRC) and four photometric bands at 65 micrometers (N60), 90 micrometers (WIDE-S), 140 micrometers (WIDE-L) and 160 micrometers (N160) of the Far-infrared Surveyor (FIS). This allows us to systematically examine the temporal evolution of the infrared spectral energy distributions (SEDs) of novae over epochs from 2006 May to 2007 August every six months. We have searched for infrared counter part of 57 targets including classical novae, recurrent novae and dusty CV, which have been observed with multi-wavelengths. In the AKARI IRC/FIS all sky surveys, 3 novae, V445 Pup, RR Tel, and V838 Mon, were detected both in the mid-infrared and far-infrared. Nine other novae, T CrB, DZ Cru, V2361 Cyg, V476 Sct, RS Oph, V2362 Cyg, V1065 Cen, V1280 Sco, and V745 Sco, were detected only in the mid-infrared. We have investigated the properties of infrared emission associated with those targets. In particular, for some objects, the temporal evolution of infrared emissions before and after the dust formation episode in the nova ejecta is discussed....

We aim to study star-forming galaxies by using a blind spectroscopic survey at mid-infrared (MIR) wavelengths to understand evolution of their star formation rate (SFR) and specific SFR (SFR per stellar mass) up to z in the order of 0.5, by paying particular attention to their Polycyclic Aromatic Hydrocarbon (PAH) properties. We conducted a low-resolution (R approximately equal to 50) slitless spectroscopic survey at 5-13 micrometers of 9 micrometers flux-selected sources (approximately greater than 0.3 mJy) around the North Ecliptic Pole with the Infrared Camera (IRC) onboard AKARI. We identified 48 PAH galaxies with PAH 6.2, 7.7, and 8.6 micrometers features at z approximately less than 0.5. The rest-frame optical-MIR spectral energy distributions (SEDs) based on CFHT and AKARI/IRC imaging are produced and analyzed in conjunction with the PAH spectroscopy. The rest-frame SEDs of all PAH galaxies have a universal shape with stellar and 7.7 micrometers (PAH) bumps, except that the PAH enhancement (luminosity ratio of the 7.7 micrometers PAH feature over the 3.5 micrometers stellar bump) significantly varies as a function of the PAH luminosities. We identified a PAH-enhanced population at z approximately less than 0.35, whose SEDs and luminosities are typical of luminous infrared galaxies. They show particularly larger PAH enhancement at high luminosity, implying that they are vigorous star-forming galaxies with elevated specific SFR. Our composite starburst model that combines a young and dusty starburst with a very old population can successfully reproduce most SED characteristics....

AKARI/IRC is capable of conducting slit-less spectroscopy in the mid-infrared (5-13 μm) over a 10' × 10' area with a spectral resolution of 50, which is suitable for serendipitous surveys. The data reduction is, however, rather complicated by the confusion of nearby sources after dispersing the spectra. To achieve efficient and reliable data reduction, we first compiled a point-source list from the reference image in each field of view and checked the overlaps of the spectra using their relative positions and fluxes. Applying this procedure to 886 mid-infrared slit-less spectroscopic data taken in the cryogenic phase, we obtained 862 mid-infrared spectra from 604 individual non-overlapping sources brighter than 1.5 mJy. We find a variety of objects in the spectroscopic catalogue, ranging from stars to galaxies. We also obtained a by-product catalogue of 9 μm point sources containing 42837 objects brighter than 0.3 mJy. The spectroscopic and point-source catalogues are available online....

We present the current status of the AKARI slitless spectroscopic catalogue, which is produced as a part of the AKARI data archive activities. AKARI has capability of slitless spectroscopy in the NIR and MIR wavelengths for a 10' x 10' area. The data reduction is, however, very difficult due to a confusion of nearby sources after dispersion. In order to solve the problem, we first make a point source list in each FOV from the reference image, and evaluate overlaps between the spectra based on their positions and fluxes. As a trial, we applied the procedure to the Phase 2 MIR-S data (5-3 micrometers). As a result of processing all reference images of 884 spectroscopic observations, 42,000 point sources (at lambda = 9 micrometers) are extracted with a detection limit of 0.3 mJy. Based on the source list, we identified the non-overlapped sources and extracted their spectra. We obtained MIR spectra of 880 objects including main sequence stars, AGB stars, galaxies, and AGNs. The dataset is valuable as an unbiased spectral sample in the MIR. The point source and spectroscopic catalogues will be publicly released in the near future....

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AKARI performed about 10,000 spectroscopic observations with the Infrared Camera (IRC) during its mission phase. These IRC observations provide unique spectroscopic data at near- and mid-infrared wavelengths for studies of the next few decades because of its high sensitivity and unique wavelength coverage. In this paper, we present the current status of the activity for improving the IRC spectroscopic data reduction process, including the toolkit and related data packages, and also discuss the goal of this project....

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MIMIZUKU is the first-generation mid-infrared instrument for the university of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU provides imaging and spectroscopic monitoring capabilities in a wide wavelength range from 2 to 38 μm, including unique bands like 2.7-μm and 30-μm band. Recently, we decided to add spectroscopic functions, KL-band mode (λ= 2.1-4.0 μm R =λ/∆λ 210) and 2.7-μm band mode ( λ= 2.4-2.95 μm R 620), and continuous spectroscopic coverage from 2.1 to 26 μm is realized by this update. Their optical designing is completed, and fabrications of optical elements are ongoing. As recent progress, we also report the completion of the cryogenic system and optics. The cryogenic system has been updated by changing materials and structures of thermal links, and the temperatures of the optical bench and detector mounting stages finally achieved required temperatures. Their stability against instrument attitude is also confirmed through an inclination test. As for the optics, its gold-plated mirrors have been recovered from galvanic corrosion by refabrication and reconstruction. Enough image quality and stability are confirmed by room-temperature tests. MIMIZUKU is intended to be completed in this autumn, and commissioning at the Subaru telescope and scientific operations on the TAO telescope are planned in 2017 and around 2019, respectively. In this paper, these development activities and future prospects of MIMIZUKU are reported. <P />...