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.

MIMIZUKU is the first-generation mid-infrared instrument for the TAO 6.5-m telescope. It has three internal optical channels to cover a wide wavelength range from 2 to 38 mu m. Of the three channels, the NIR channel is responsible for observations in the shortest wavelength range, shorter than 5.3 mu m. The performance of the NIR channel is evaluated in the laboratory. Through the tests, we confirm the followings: 1) the detector (HAWAII-1RG with 5.3-mu m cutoff) likely achieves similar to 80% quantum efficiency; 2) imaging performance is sufficient to achieve seeing-limit spatial resolution; 3) system efficiencies in imaging modes are 2.4-31%; and 4) the system efficiencies in spectroscopic modes is 5-18%. These results suggest that the optical performance of the NIR channel is achieved as expected from characteristics of the optical components. However, calculations of the background levels and on-sky sensitivity based on these results suggest that neutral density (ND) filters are needed to avoid saturation in L'- and M'-band observations and that the ND filters and the entrance window, made of chemical-vapor-deposition (CVD) diamond, significantly degrade the sensitivity in these bands. This means that the use of different window materials and improvements of the detector readout speed are required to achieve both near-infrared and long-wavelength mid-infrared (>30 mu m) observations.

We report the results of video observations of tiny (diameter less than 100 m) near-Earth objects (NEOs) with Tomo-e Gozen on the Kiso 105 cm Schmidt telescope. The rotational period of a tiny asteroid reflects its dynamical history and physical properties since smaller objects are sensitive to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. We carried out video observations of 60 tiny NEOs at 2 fps from 2018 to 2021 and successfully derived the rotational periods and axial ratios of 32 NEOs including 13 fast rotators with rotational periods less than 60 s. The fastest rotator found during our survey is 2020 HS7 with a rotational period of 2.99 s. We statistically confirmed that there is a certain number of tiny fast rotators in the NEO population, which have been missed with all previous surveys. We have discovered that the distribution of the tiny NEOs in a diameter and rotational period (D-P) diagram is truncated around a period of 10 s. The truncation with a flat-top shape is not explained well by either a realistic tensile strength of NEOs or the suppression of YORP by meteoroid impacts. We propose that the dependence of the tangential YORP effect on the rotational period potentially explains the observed pattern in the D-P diagram.

We report the results of video observations of tiny (diameter less than 100 m) near-Earth objects (NEOs) with Tomo-e Gozen on the Kiso 105 cm Schmidt telescope. The rotational period of a tiny asteroid reflects its dynamical history and physical properties since smaller objects are sensitive to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. We carried out video observations of 60 tiny NEOs at 2 fps from 2018 to 2021 and successfully derived the rotational periods and axial ratios of 32 NEOs including 13 fast rotators with rotational periods less than 60 s. The fastest rotator found during our survey is 2020 HS7 with a rotational period of 2.99 s. We statistically confirmed that there is a certain number of tiny fast rotators in the NEO population, which have been missed with all previous surveys. We have discovered that the distribution of the tiny NEOs in a diameter and rotational period (D-P) diagram is truncated around a period of 10 s. The truncation with a flat-top shape is not explained well by either a realistic tensile strength of NEOs or the suppression of YORP by meteoroid impacts. We propose that the dependence of the tangential YORP effect on the rotational period potentially explains the observed pattern in the D-P diagram.

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....

Using a prototype of the Tomo-e Gozen wide-field CMOS mosaic camera, we acquire wide-field optical images at a cadence of 2 Hz and search them for transient sources of duration 1.5 to 11.5 s. Over the course of eight nights, our survey encompasses the equivalent of roughly two days on one square degree, to a fluence equivalent to a limiting magnitude of about V= 15.6 in a 1-s exposure. After examining by-eye the candidates identified by a software pipeline, we find no sources which meet all our criteria. We compute upper limits to the rate of optical transients consistent with our survey, and compare those to the rates expected and observed for representative sources of ephemeral optical light.

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....

We present a new calibration for the second-order light contamination in the near-infrared grism spectroscopy with the Infrared Camera aboard AKARI, specifically for the post-cryogenic phase of the satellite (Phase 3). Following our previous work on the cryogenic phase (Phases 1 and 2), the wavelength and spectral response calibrations were revised. Unlike Phases 1 and 2, during Phase 3 the temperature of the instrument was not stable and gradually increased from 40 to 47 K. To assess the effect of the temperature increase, we divided Phase 3 into three sub-phases and performed the calibrations separately. As in Phases 1 and 2, we confirmed that there was contamination due to the wavelength dependence of the refractive index of the grism material in every sub-phase. The wavelength calibration curves for the three sub-phases coincided with each other and did not show any significant temperature dependence. The response decreased with temperature by similar to 10% from the beginning to the end of Phase 3. We approximated the temperature dependence of the response at a linear relation and derived a correction factor as a function of temperature. The relative fraction of the second-order light contamination to the first-order light was found to be 25% smaller than that in Phases 1 and 2.

© 2018 Elsevier Ltd Imaging observations of faint meteors were carried out on April 11 and 14, 2016 with a wide-field CMOS mosaic camera, Tomo-e PM, mounted on the 105-cm Schmidt telescope at Kiso Observatory, the University of Tokyo. Tomo-e PM, which is a prototype model of Tomo-e Gozen, can monitor a sky of ∼1.98deg2 at 2 Hz. The numbers of detected meteors are 1514 and 706 on April 11 and 14, respectively. The detected meteors are attributed to sporadic meteors. Their absolute magnitudes range from +4 to +10mag in the V-band, corresponding to about 8.3×10−2 to 3.3×10−4g in mass. The present magnitude distributions we obtained are well explained by a single power-law luminosity function with a slope parameter r=3.1±0.4 and a meteor rate log10N0=−5.5±0.5. The results demonstrate a high performance of telescopic observations with a wide-field video camera to constrain the luminosity function of faint meteors. The performance of Tomo-e Gozenis about two times higher than that of Tomo-e PM. A survey with Tomo-e Gozenwill provide a more robust measurement of the luminosity function.

Knowledge of water in the solar system is important for the understanding of a wide range of evolutionary processes and the thermal history of the solar system. To explore the existence of water in the solar system, it is indispensable to investigate hydrated minerals and/or water ice on asteroids. These water-related materials show absorption features in the 3 μm band (wavelengths from 2.7 to 3.1 μm). We conducted a spectroscopic survey of asteroids in the 3 μm band using the Infrared Camera (IRC) on board the Japanese infrared satellite AKARI. In the warm mission period of AKARI, 147 pointed observations were performed for 66 asteroids in the grism mode for wavelengths from 2.5 to 5 μm. According to these observations, most C-complex asteroids have clear absorption features (>10% with respect to the continuum) related to hydrated minerals at a peak wavelength of approximately 2.75 μm, while S-complex asteroids have no significant features in this wavelength range. The present data are released to the public as the Asteroid Catalog using AKARI Spectroscopic Observations (AcuA-spec)....

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....

The AKARI IRC all-sky survey provided more than twenty thousand thermal infrared observations of over five thousand asteroids. Diameters and albedos were obtained by fitting an empirically calibrated version of the standard thermal model to these data. After the publication of the flux catalogue in October 2016, our aim here is to present the AKARI IRC all-sky survey data and discuss valuable scientific applications in the field of small body physical properties studies. As an example, we update the catalogue of asteroid diameters and albedos based on AKARI using the near-Earth asteroid thermal model (NEATM). We fit the NEATM to derive asteroid diameters and, whenever possible, infrared beaming parameters. We fit groups of observations taken for the same object at different epochs of the survey separately, so we compute more than one diameter for approximately half of the catalogue. We obtained a total of 8097 diameters and albedos for 5170 asteroids, and we fitted the beaming parameter for almost two thousand of them. When it was not possible to fit the beaming parameter, we used a straight line fit to our sample's beaming parameter-versus-phase angle plot to set the default value for each fit individually instead of using a single average value. Our diameters agree with stellar-occultation-based diameters well within the accuracy expected for the model. They also match the previous AKARI-based catalogue at phase angles lower than 50°, but we find a systematic deviation at higher phase angles, at which near-Earth and Mars-crossing asteroids were observed. The AKARI IRC All-sky survey is an essential source of information about asteroids, especially the large ones, since, it provides observations at different observation geometries, rotational coverages and aspect angles. For example, by comparing in more detail a few asteroids for which dimensions were derived from occultations, we discuss how the multiple observations per object may already provide three-dimensional information about elongated objects even based on an idealised model like the NEATM. Finally, we enumerate additional expected applications for more complex models, especially in combination with other catalogues.

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 a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU2, which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU2 are 44.6 ± 0.5% in the RC band and 44.0 ± 0.6% in the V band at a solar phase angle of 81.0°. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (&lt 0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU2 has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.

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....

© 2018 SPIE. The Tomo-e Gozen is a wide-field high-speed camera for the Kiso 1.0-m Schmidt telescope, with a field-of-view of 20.7-deg2 covered by 84 chips of 2k x 1k CMOS image sensors with 19-μm pixels. It is capable to take consecutive images at 2-fps in full-frame read with an absolute time accuracy of 0.2 millisecond. The sensors are operated without mechanical coolers owing to a low dark current at room temperature. A low read noise of 2-e- achieves higher sensitivity than that with a CCD sensor in short exposures. Big data of 30-TBytes per night produced in the 2-fps observations is processed in real-time to quickly detect transient events and issue alerts for follow-ups.

© 2018 SPIE. Tomo-e Gozen (Tomo-e) is a wide field optical camera for the Kiso 1.05 m f/3.1 Schmidt telescope operated by the University of Tokyo. Tomo-e is equipped with 84 chips of front-illuminated CMOS image sensors with a microlens array. The field of view is about 20 square degrees and maximum frame rate is 2 fps. The CMOS sensor has 2160 × 1200 pixels and a size of pixel is 19 microns, which is larger than those of other CMOS sensors. We have evaluated performances of the CMOS sensors installed in Tomo-e. The readout noise is 2.0 e- in 2 fps operations when an internal amplifier gain is set to 16. The dark current is 0.5 e-/sec/pix at room temperature, 290K, which is lower than a typical sky background flux in Tomo-e observations, 50 e-/sec/pix. The efficiency of the camera system peaks at approximately 0.7 in 500 nm.

In the 1-2.5 μm range, spectroscopic observations are made on the AcuA-spec asteroids, the spectra of which were obtained in a continuous covered mode between 2.5-5.0 μm by AKARI. Based on the Bus-DeMeo taxonomy (DeMeo et al. 2009, Icarus, 202, 160), all the AcuA-spec asteroids are classified, using both published and our observational data. Additionally, taking advantage of the Bus-DeMeo taxonomy characteristics, we constrain the characteristic of each spectral type by combining the taxonomy results with the other physical observational data from colorimetry, polarimetry, radar, and radiometry. As a result, it is suggested that certain C-, Cb-, B-type, dark X-, and D-complex asteroids have spectral properties compatible with those of anhydrous interplanetary dust particles with tiny bright material, such as water ice. This supports the proposal regarding the C-complex asteroids (Vernazza et al. 2015, ApJ, 806, 204; 2017, AJ, 153, 72). A combination of the Bus-DeMeo taxonomy for AcuA-spec asteroids with other physical clues, such as the polarimetric inversion angle, radar albedo, and mid-infrared spectroscopic spectra, will be beneficial for surface material constraints from the AcuA-spec asteroid observations....

We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles alpha = 57 degrees-141 degrees around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are P-max = 7.32 +/- 0.25% at phase angles of alpha(max) = 124 degrees +/- 8 degrees in the V-band and P-max = 7.04 +/- 0.21% at alpha(max) = 124 degrees +/- 6 degrees in the RC-band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of p(V) = 0.25 +/- 0.02, which is in agreement with that of Q-type taxonomic asteroids. amax is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance q = 0.187 au and a short rotational period of T-rot = 2.27 hr) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon.

We investigated the physical properties of the comet-like objects 107P/(4015) Wilson-Harrington (4015WH) and P/2006 HR30 (Siding Spring; HR30) by applying a simple thermophysical model to the near-infrared spectroscopy and broadband observation data obtained by the AKARIsatellite of JAXA when they showed no detectable comet-like activity. We selected these two targets because the tendency of thermal inertia to decrease with the size of an asteroid, which has been demonstrated in recent studies, has not been confirmed for comet-like objects. It was found that 4015WH, which was originally discovered as a comet but has not shown comet-like activity after its discovery, has effective size D = 3.74-4.39 km and geometric albedo pV approximate to 0.040-0.055 with thermal inertia T = 100-250 J m(-2) K-1 s(-1/2). The corresponding grain size is estimated as 1-3 mm. We also found that HR30, which was observed as a bare cometary nucleus at the time of our observation, has D = 23.9-27.1km and pV 0.035 - 0.045 with T = 250-1000 J m(-2) K-1 s(-1/2). We conjecture the pole latitude -20 degrees less than or similar to beta(S) less than or similar to +60 degrees The results for both targets are consistent with previous studies. Based on the results, we propose that comet-like objects are not clearly distinguishable from their asteroidal counterparts on the D-G plane.

Organized Autotelescopes for Serendipitous Event Survey (OASES) is an optical observation project that aims to detect and investigate stellar occultation events by kilometer-sized trans-Neptunian objects (TNOs). In this project, multiple low-cost observation systems for wide-field and high-speed photometry were developed in order to detect rare and short-timescale stellar occultation events. The observation system consists of commercial off-the-shelf 0.28m aperture f/1.58 optics providing a 2.degrees 3 x 1.degrees 8 field of view. A commercial CMOS camera is coupled to the optics to obtain full-frame imaging with a frame rate greater than 10 Hz. As of 2016 September, this project exploits two observation systems, which are installed on Miyako Island, Okinawa, Japan. Recent improvements in CMOS technology in terms of high-speed imaging and low readout noise mean that the observation systems are capable of monitoring similar to 2000 stars in the Galactic plane simultaneously with magnitudes down to V similar to 13.0, providing similar to 20% photometric precision in light curves with a sampling cadence of 15.4 Hz. This number of monitored stars is larger than for any other existing instruments for coordinated occultation surveys. In addition, a precise time synchronization method needed for simultaneous occultation detection is developed using faint meteors. The two OASES observation systems are executing coordinated monitoring observations of a dense stellar field in order to detect occultations by kilometer-sized TNOs for the first time.

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The JAXA Hayabusa-2 mission was approved in 2010 and launched on December 3, 2014. The spacecraft will arrive at the near-Earth asteroid 162173 Ryugu ( 1999 JU(3)) in 2018 where it will perform a survey, land and obtain surface material, then depart in December 2019 and return to Earth in December 2020. We observed Ryugu with the Herschel Space Observatory in April 2012 at far-infrared thermal wavelengths, supported by several ground-based observations to obtain optical lightcurves. We reanalysed previously published Subaru-COMICS and AKARI-IRC observations and merged them with a Spitzer-IRS data set. In addition, we used a large set of Spitzer-IRAC observations obtained in the period January to May, 2013. The data set includes two complete rotational lightcurves and a series of ten "point-and-shoot" observations, all at 3.6 and 4.5 mu m. The almost spherical shape of the target together with the insufficient lightcurve quality forced us to combine radiometric and lightcurve inversion techniques in different ways to find the object's spin-axis orientation, its shape and to improve the quality of the key physical and thermal parameters. Handling thermal data in inversion techniques remains challenging: thermal inertia, roughness or local structures influence the temperature distribution on the surface. The constraints for size, spin or thermal properties therefore heavily depend on the wavelengths of the observations. We find that the solution which best matches our data sets leads to this C class asteroid having a retrograde rotation with a spin-axis orientation of (lambda = 310 degrees - 340 degrees beta = -40 degrees +/- similar to 15 degrees) in ecliptic coordinates, an effective diameter ( of an equal-volume sphere) of 850 to 880 m, a geometric albedo of 0.044 to 0.050 and a thermal inertia in the range 150 to 300 Jm(-2) s (-0.5) K-1. Based on estimated thermal conductivities of the top-layer surface in the range 0.1 to 0.6 WK-1 m(-1), we calculated that the grain sizes are approximately equal to between 1 and 10 mm. The finely constrained values for this asteroid serve as a "design reference model", which is currently used for various planning, operational and modelling purposes by the Hayabusa-2 team.

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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The Tomo-e Gozen camera is a next-generation extremely wide-field optical camera, equipped with 84 CMOS sensors. The camera records about a 20 square-degree area at 2 Hz, providing "astronomical movie data". We have developed a prototype of the Tomo-e Gozen camera (hereafter, Tomo-e PM), to evaluate the basic design of the Tomo-e Gozen camera. Tomo-e PM, equipped with 8 CMOS sensors, can capture a 2 square-degree area at up to 2 Hz. Each CMOS sensor has about 2.6 M pixels. The data rate of Tomo-e PM is about 80 MB/s, corresponding to about 280 GB/hour. We have developed an operating system and reduction softwares to handle such a large amount of data. Tomo-e PM was mounted on 1.0-m Schmidt Telescope in Kiso Observatory at the University of Tokyo. Experimental observations were carried out in the winter of 2015 and the spring of 2016. The observations and software implementation were successfully completed. The data reduction is now in execution.

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 />...

Zodiacal emission is thermal emission from interplanetary dust. Its contribution to the sky brightness is non-negligible in the region near the ecliptic plane, even in the far-infrared (far-IR) wavelength regime. We analyze zodiacal emission observed by the AKARI far-IR all-sky survey, which covers 97% of the entire sky at arcminute-scale resolution in four photometric bands, with central wavelengths of 65, 90, 140, and 160 mu m. AKARI detected small-scale structures in the zodiacal dust cloud, including the asteroidal dust bands and the circumsolar ring, at far-IR wavelengths. Although the smooth component of the zodiacal emission structure in the far-IR sky can be reproduced well by models based on existing far-IR observations, previous zodiacal emission models have discrepancies in the small-scale structures compared with observations. We investigate the geometry of the small-scale dust-band structures in the AKARI far-IR all-sky maps and construct template maps of the asteroidal dust bands and the circumsolar ring components based on the AKARI far-IR maps. In the maps, +/- 1 degrees.4, +/- 2 degrees.1, and +/- 10 degrees asteroidal dust-band structures are detected in the 65 mu m and 90 mu m bands. A possible +/- 17 degrees band may also have been detected. No evident dust-band structures are identified in either the 140 mu m or the 160 mu m bands. By subtracting the dust-band templates constructed in this paper, we can achieve a similar level of flux calibration of the AKARI far-IR all-sky maps in the vertical bar beta vertical bar &lt; 40 degrees region to that in the region for vertical bar beta vertical bar &gt; 40 degrees.

The Japanese infrared astronomical satellite AKARI performed ̃4000 pointed observations for 16 months until the end of August 2007, 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 recent updates on calibration processes of near- and mid-infrared images taken by the Infrared Camera (IRC), which has nine photometric filters covering 2-27 μm continuously. Using the latest data reduction toolkit, we created calibrated and stacked images from each pointed observation. About 90% of the stacked images have a position accuracy better than 1{^&#039;&#039;&lt;SUB&gt;.&lt;/SUB&gt;}5. Uncertainties in aperture photometry estimated from a typical standard sky deviation of stacked images are a factor of ̃2-4 smaller than those of AllWISE at similar wavelengths. The processed images, together with documents such as process logs, as well as the latest toolkit are available online....

We perform revised spectral calibrations for the AKARI near-infrared grism to correct quantitatively for the effect of the wavelength-dependent refractive index. The near-infrared grism covering the wavelength range of 2.5-5.0 mu m, with a spectral resolving power of 120 at 3.6 mu m, is found to be contaminated by second-order light at wavelengths longer than 4.9 mu m, which is especially serious for red objects. First, we present the wavelength calibration considering the refractive index of the grism as a function of the wavelength for the first time. We find that the previous solution is positively shifted by up to 0.01 mu m compared with the revised wavelengths at 2.5-5.0 mu m. In addition, we demonstrate that second-order contamination occurs even with a perfect order-sorting filter owing to the wavelength dependence of the refractive index. Secondly, the spectral responses of the system from the first-and second-order light are simultaneously obtained from two types of standard objects with different colors. The response from the second-order light suggests leakage of the order-sorting filter below 2.5 mu m. The relations between the output of the detector and the intensities of the first- and second-order light are formalized by a matrix equation that combines the two orders. The removal of the contaminating second-order light can be achieved by solving the matrix equation. The new calibration extends the available spectral coverage of the grism mode from 4.9 mu m up to 5.0 mu m. The revision can be used to study spectral features falling in these extended wavelengths, e. g., the carbon monoxide fundamental ro-vibrational absorption within nearby active galactic nuclei.