奥村 真一郎

ABSTRACT The population of optical transients evolving within a time-scale of a few hours or a day (so-called fast optical transients, FOTs) has recently been debated extensively. In particular, our understanding of extragalactic FOTs and their rates is limited. We present a search for extragalactic FOTs with the Tomo-e Gozen high-cadence survey. Using the data taken from 2019 August to 2022 June, we obtain 113 FOT candidates. Through light curve analysis and cross-matching with other survey data, we find that most of these candidates are in fact supernovae, variable quasars, and Galactic dwarf novae that were partially observed around their peak brightness. We find no promising candidate of extragalactic FOTs. From this non-detection, we obtain upper limits on the event rate of extragalactic FOTs as a function of their time-scale. For a very luminous event (absolute magnitude M < −26 mag), we obtain the upper limits of 4.4 × 10−9 Mpc−3 yr−1 for a time-scale of 4 h, and 7.4 × 10−10 Mpc−3 yr−1 for a time-scale of 1 d. Thanks to our wide (although shallow) surveying strategy, our data are less affected by the cosmological effects, and thus, give one of the more stringent limits to the event rate of intrinsically luminous transients with a time-scale of <1 d.

Abstract We report on a one-second-cadence wide-field survey for M-dwarf flares using the Tomo-e Gozen camera mounted on the Kiso Schmidt telescope. We detect 22 flares from M3–M5 dwarfs with a rise time of 5 s ≲ trise ≲ 100 s and an amplitude of 0.5 ≲ ΔF/F⋆ ≲ 20. The flare light-curves mostly show steeper rises and shallower decays than those obtained from the Kepler one-minute cadence data and tend to have flat peak structures. Assuming a blackbody spectrum with a temperature of 9000–15000 K, the peak luminosities and energies are estimated to be 1029 erg s−1 ≲ Lpeak ≲ 1031 erg s−1 and 1031 erg ≲ Eflare ≲ 1034 erg, which constitutes the bright end of fast optical flares for M dwarfs. We confirm that more than $90\%$ of the host stars of the detected flares are magnetically active based on their Hα-emission-line intensities obtained by LAMOST. An estimated occurrence rate of detected flares is ∼0.7 per day per active star, indicating they are common in magnetically active M dwarfs. We argue that the flare light-curves can be explained by the chromospheric compression model: the rise time is broadly consistent with the Alfvén transit time of a magnetic loop with a length scale of lloop ∼ 104 km and a field strength of 1000 gauss, while the decay time is likely determined by the radiative cooling of the compressed chromosphere down near to the photosphere with a temperature of ≳ 10000 K. These flares from M dwarfs could be a major contamination source for a future search of fast optical transients of unknown types.

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 conduct 24.4 fps optical observations of repeating fast radio burst (FRB) 20190520B using Tomo-e Gozen, a high-speed CMOS camera mounted on the Kiso 105 cm Schmidt telescope, simultaneously with radio observations carried out using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We succeeded in the simultaneous optical observations of 11 radio bursts that FAST detected. However, no corresponding optical emission was found. The optical fluence limits as deep as 0.068 Jy ms are obtained for the individual bursts (0.029 Jy ms on the stacked data) corrected for the dust extinction in the Milky Way. The fluence limit is deeper than those obtained in the previous simultaneous observations for an optical emission with a duration greater than or similar to 0.1 ms. Although the current limits on radio-optical spectral energy distribution (SED) of FRBs are not constraining, we show that SED models based on observed SEDs of radio variable objects such as optically detected pulsars, and a part of parameter spaces of theoretical models in which FRB optical emission is produced by inverse Compton scattering in a pulsar magnetosphere or a strike of a magnetar blastwave into a hot wind bubble, can be ruled out once a similar fluence limit as in our observation is obtained for a bright FRB with a radio fluence greater than or similar to 5 Jy ms.

In this Letter we report a discovery of a prominent flash of a peculiar overluminous Type Ia supernova, SN 2020hvf, in about 5 hr of the supernova explosion by the first wide-field mosaic CMOS sensor imager, the Tomo-e Gozen Camera. The fast evolution of the early flash was captured by intensive intranight observations via the Tomo-e Gozen high-cadence survey. Numerical simulations show that such a prominent and fast early emission is most likely generated from an interaction between 0.01 M (circle dot) circumstellar material (CSM) extending to a distance of similar to 10(13) cm and supernova ejecta soon after the explosion, indicating a confined dense CSM formation at the final evolution stage of the progenitor of SN 2020hvf. Based on the CSM-ejecta interaction-induced early flash, the overluminous light curve, and the high ejecta velocity of SN 2020hvf, we suggest that the SN 2020hvf may originate from a thermonuclear explosion of a super-Chandrasekhar-mass white dwarf ("super-M (Ch) WD"). Systematical investigations on explosion mechanisms and hydrodynamic simulations of the super-M (Ch) WD explosion are required to further test the suggested scenario and understand the progenitor of this peculiar supernova.

This paper describes the guidance and navigation technique used by Hayabusa2 for the asteroid rendezvous operation to reach Ryugu. The operation results, including the achieved guidance and navigation performance, are also summarized. Multiple assessment and navigation teams worked closely to provide reliable navigation solutions with a short solution delivery cycle. Although the uncertainty of the Ryugu’s ephemeris was considerable before Hayabusa2’s arrival, a combination of radiometric-optical hybrid navigation and a stochastic-constrained optimum guidance method was able to achieve an accuracy of less than 100 m and 1 cm/s, and the arrival was precisely timed.

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.

We report observations of a stellar occultation by the classical Kuiper Belt object (50000) Quaoar that occurred on 2019 June 28. A single-chord high-cadence (2 Hz) photometry data set was obtained with the Tomo-e Gozen CMOS camera mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The obtained ingress and egress data do not show any indication of atmospheric refraction and allow new 1? and 3? upper limits of 6 and 16 nbar, respectively, to be set for the surface pressure of a pure methane atmosphere. These upper limits are lower than the saturation vapor pressure of methane at Quaoar?s expected mean surface temperature (T?44 K) and imply the absence of a ?10 nbar-level global atmosphere formed by methane ice on Quaoar?s surface.

We present visible and near-infrared observations of a near-Earth object (NEO), 2012 TC4. The NEO 2012 TC4 approached close to Earth at a distance of about 50,000 km in 2017 October. This close approach provided a practical exercise for planetary defense. This apparition was also an appropriate opportunity to investigate 2012 TC4, which is a monolithic asteroid. We conducted the observation campaign of 2012 TC4 using six small- and medium-sized telescopes. The multiband photometry analysis showed the taxonomic class of 2012 TC4 to be an X type. In particular, we successfully obtained the high time resolution light curve of 2012 TC4 with the Tomo-e Gozen camera, which is the world's first wide-field CMOS camera, mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The shape and rotational motion models of 2012 TC4 were derived from the light curve. When 2012 TC4 was assumed to be a triaxial ellipsoid, the rotational and precession periods were 8.47 +/- 0.01 minutes and 12.25 +/- 0.01 minutes, respectively, with the long-axis mode. This indicates that 2012 TC4 is a tumbling and monolithic asteroid. The shape models showed the plausible axial lengths to be 6.2 x 8.0 x 14.9 m or 3.3 x 8.0 x 14.3 m. The flattened and elongated shape indicates that 2012 TC4 is a fragment produced by an impact event. We also estimated the excitation timescale, which implied that the impact event happened within similar to 3 x 10(5) yr and 2012 TC4 has a fresh surface.

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 similar to 1.98deg(2) 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 +10 mag in the V-band, corresponding to about 8.3 x 10(-2) to 3.3 x 10(-4) g 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 log(10)N(0) = -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.

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.

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 2160x1200 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.

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-deg(2) covered by 84 chips of 2k x 1k CMOS image sensors with 19-mu m 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.

The Japan Aerospace Exploration Agency (JAXA) is developing a new observation technology for Near Earth Objects (NEOs). The technology employs a very different process compared to existing NEO survey programs such as Pan-Starrs and CSS, and could possibly innovate the current NEO survey concept. It uses many CCD images in which to detect faint and fast moving NEOs. The FPGA (field programmable gate array) board is used to reduce analysis time. We discovered two NEOs using 18-cm telescopes in January 2017. This marked Japan's first discovery of NEOs in about nine years.

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.

The Tomo-e Gozen is an extremely wide-field optical camera for the Kiso 1.0-m Schmidt telescope. It is capable of taking consecutive frames with a field-of-view of 20 deg(2) and a sub-second time-resolution, which are achieved by 84 chips of 2k x 1k CMOS sensor. This camera adopts unconventional designs including a lightweight structure, a non-vacuumed and naturally-air cooled system, front-side-illuminated CMOS sensors with microlens arrays, a sensor alignment along a spherical focal plane of the telescope, and massive readout electronics. To develop technical components necessary for the Tomo-e Gozen and confirm a feasibility of its basic design, we have developed a prototype-model (PM) of the Tomo-e Gozen prior to the final-model (FM). The Tomo-e PM is equipped with eight chips of the CMOS sensor arranged in a line along the RA direction, covering a sky area of 2.0 deg(2). The maximum frame rate is 2 fps. The total data production rate is 80 MByte sec(-1) at 2 fps, corresponding to approximately 3 TByte night(-1). After laboratory testing, we have successfully obtained consecutive movie data at 2 fps with the Tomo-e PM in the first commissioning run conducted in the end of 2015.

We present a photometric campaign targeted at asteroids that display both long periods of rotation and small amplitudes of brightness variations. Our aim is to de bias available sample of spin and shape modelled asteroids and to correct previous wrong period determinations. Our newest findings are corrected period determinations for asteroids (279) Thule (P=23.896 +/- 0.005 h), (673) Edda (P=22.340 +/- 0.004 h), and (737) Arequipa (P=7.0259 +/- 0.0003 h). Supporting lightcurves are presented in this paper.

Physical studies of asteroids depend on an availability of lightcurve data. Targets that are easy to observe and analyse naturally have more data available, so their synodic periods are confirmed from multiple sources. Also, thanks to availability of data from a number of apparitions, their spin and shape models can often be obtained, with a precise value of sidereal period and spin axis coordinates. Almost half of bright (H <= 11 mag) main-belt asteroid population with known lightcurve parameters have rotation periods considered long (P >= 12 h) and are rarely chosen for photometric observations. There is a similar selection effect against asteroids with low lightcurve amplitudes (a(max) <= 0.25 mag). As a result such targets, though numerous in this brightness range, are underrepresented in the sample of spin and shape modelled asteroids. In the range of fainter targets such effects are stronger. These selection effects can influence what is now known about asteroid spin vs. size distribution, on asteroid internal structure and densities and on spatial orientation of asteroid spin axes. To reduce both biases at the same time, we started a photometric survey of a substantial sample of those bright main-belt asteroids that displayed both features: periods longer than 12 h, and amplitudes that did not exceed 0.25 magnitude. First we aim at finding synodic periods of rotation, and after a few observed apparitions, obtaining spin and shape models of the studied targets. As an initial result of our survey we found that a quarter of the studied sample (8 out of 34 targets) have rotation periods different from those widely accepted. We publish here these newly found period values with the lightcurves. The size/frequency plot might in reality look different in the long-period range. Further studies of asteroid spins, shapes, and structure should take into account serious biases that are present in the parameters available today. Photometric studies should concentrate on such difficult targets to remove the biases and to complete the sample. (C) 2015 Elsevier Ltd. All rights reserved.

Aims. Astrometric observations performed by the Gaia Follow-Up Network for Solar System Objects (Gaia-FUN-SSO) play a key role in ensuring that moving objects first detected by ESA's Gaia mission remain recoverable after their discovery. An observation campaign on the potentially hazardous asteroid (99 942) Apophis was conducted during the asteroid's latest period of visibility, from 12/21/2012 to 5/2/2013, to test the coordination and evaluate the overall performance of the Gaia-FUN-SSO . Methods. The 2732 high quality astrometric observations acquired during the Gaia-FUN-SSO campaign were reduced with the Platform for Reduction of Astronomical Images Automatically (PRAIA), using the USNO CCD Astrograph Catalogue 4 (UCAC4) as a reference. The astrometric reduction process and the precision of the newly obtained measurements are discussed. We compare the residuals of astrometric observations that we obtained using this reduction process to data sets that were individually reduced by observers and accepted by the Minor Planet Center. Results. We obtained 2103 previously unpublished astrometric positions and provide these to the scientific community. Using these data we show that our reduction of this astrometric campaign with a reliable stellar catalog substantially improves the quality of the astrometric results. We present evidence that the new data will help to reduce the orbit uncertainty of Apophis during its close approach in 2029. We show that uncertainties due to geolocations of observing stations, as well as rounding of astrometric data can introduce an unnecessary degradation in the quality of the resulting astrometric positions. Finally, we discuss the impact of our campaign reduction on the recovery process of newly discovered asteroids.

Multi-wavelength observations of the black widow binary system 2FGL J2339.6-0532 are reported. The Fermi gamma-ray source 2FGL J2339.6-0532 was recently categorized as a black widow in which a recycled millisecond pulsar (MSP) is evaporating the companion star with its powerful pulsar wind. Our optical observations show clear sinusoidal light curves due to the asymmetric temperature distribution of the companion star. Assuming a simple geometry, we constrained the range of the inclination angle of the binary system to 52 degrees < i < 59 degrees, which enables us to discuss the interaction between the pulsar wind and the companion in detail. The X-ray spectrum consists of two components: a soft, steady component that seems to originate from the surface of the MSP, and a hard, variable component from the wind-termination shock near the companion star. The measured X-ray luminosity is comparable to the bolometric luminosity of the companion, meaning that the heating efficiency is less than 0.5. In the companion orbit, 10(11) cm from the pulsar, the pulsar wind is already in the particle-dominant stage with a magnetization parameter of sigma < 0.1. In addition, we precisely investigated the time variations of the X-ray periodograms and detected a weakening of the orbital modulation. The observed phenomenon may be related to unstable pulsar wind activity or weak mass accretion, both of which can result in the temporal extinction of the radio pulse.

We have modeled two mid-infrared imaging photometry data sets to determine the spatial distribution of physical conditions in the BN/KL infrared complex. We observed the BN/KL region using the 10-m Keck I telescope and the LWS in the direct imaging mode, over a 13''x19'' field (Figure 1, left). We also modeled images obtained with COMICS (Kataza et al.2000) at the 8.2-m SUBARU telescope, over a total field of view is 31'' x 41'' (Figure 1, right), in a total of nine bands: 7.8, 8.8, 9.7, 10.5, 11.7, 12.4, 18.5, 20.8 and 24.8 mu m with similar to 1 mu m bandwidth interference filters.

"Time-Delay Integration (TDI)" readout technique has been adopted to a mosaic CCD camera equipped with four fully-depleted CCDs. Optical distortion and image deformation due to the TDI operation are discussed. The manner and advantages of the TDI method in survey observations of geosynchronous orbit objects are summarized. We propose a new TDI application method of getting short-term light curves of artificial space objects. This method of detecting a short-term variability can be applied for a variety of objects, ranging from satellites to stars. It can also be used for the light-curve observations of transient objects which might show short-term variability and of which the precise time information is needed.

スペースガードとは,地球へ接近する太陽系小天体(Near Earth Object=NEO)の発見,衝突回避の研究を行う活動である. 1990年頃より, NEOの早期発見と軌道導出を行うスペースガード観測が世界各地で行われており,現在では1万を超えるNEOが発見されている.美星スペースガードセンターは国内唯一のスペースガード観測に特化した施設であり, NEOを始めとする太陽系小天体の発見,追観測,科学観測を行っている.本稿では,スペースガード観測の現状と,美星スペースガードセンターで行われている実際の観測,さらに将来の展望について紹介する.

This paper describes a newly designed wide-band optical filter. It is optimized for deep imaging of small solar-system bodies. The new filter, which we denote as Wi, is designed to reduce contamination by light pollution from street lamps, especially strong mercury and sodium emission lines. It is also useful for reducing unwanted scattered moonlight. Compared with the use of a commercially available long-wave cut wide-band filter, the signal-to-noise ratios in the detection of asteroids are improved by about 6% by using the Wi filter.

We present lightcurve observations and multiband photometry for 107P/Wilson-Harrington using five small- and medium-sized telescopes. The lightcurve has shown a periodicity of 0.2979 day (7.15 h) and 0.0993 day (2.38 h), which has a commensurability of 3:1. The physical properties of the lightcurve indicate two models: (1) 107P/Wilson-Harrington is a tumbling object with a sidereal rotation period of 0.2979 day and a precession period of 0.0993 day. The shape has a long axis mode (LAM) of L-1:L-2:L-3 = 1.0:1.0:1.6. The direction of the total rotational angular momentum is around lambda = 310 degrees, beta = -10 degrees, or lambda = 132 degrees, beta = -17 degrees. The nutation angle is approximately constant at 65 degrees. (2) 107P/Wilson-Harrington is not a tumbler. The sidereal rotation period is 0.2979 day. The shape is nearly spherical but slightly hexagonal with a short axis mode (SAM) of L-1:L-2:L-3 = 1.5:1.5:1.0. The pole orientation is around lambda = 330 degrees, beta = -27 degrees. In addition, the model includes the possibility of binary hosting. For both models, the sense of rotation is retrograde. Furthermore, multiband photometry indicates that the taxonomy class of 107P/Wilson-Harrington is C-type. No clear rotational color variations are confirmed on the surface. (C) 2011 Elsevier Inc. All rights reserved.

We present mid-infrared narrow-band images of the Orion BN/KL region, and N-band low-resolution spectra of IRc2 and the nearby radio source "I". The distributions of the silicate absorption strength and the color temperature have been revealed with a subarcsec resolution. The detailed structure of the 7.8 mu m/12.4 mu m color temperature distribution was resolved in the vicinity of IRc2. A mid-infrared counterpart to source I has been detected as a large color temperature peak. The color temperature distribution shows an increasing gradient from IRc2 toward source 1, and no dominant temperature peak is seen at IRc2. The spectral energy distribution of IRc2 could be fitted by a two-temperature component model, and the "warmer component" of the infrared emission from IRc2 could be reproduced by scattering of radiation from source I. IRc2 itself is not self-luminous, but is illuminated and heated by an embedded luminous young stellar object located at source I.

Context. Near-Earth asteroid 162173 (1999 JU3) is a potential flyby and rendezvous target for interplanetary missions because of its easy-to-reach orbit. The physical and thermal properties of the asteroid are relevant for establishing the scientific mission goals and also important in the context of near-Earth object studies in general. Aims. Our goal was to derive key physical parameters such as shape, spin-vector, size, geometric albedo, and surface properties of 162173 (1999 JU3). Methods. With three sets of published thermal observations (ground-based N-band, Akari IRC, Spitzer IRS), we applied a thermophysical model to derive the radiometric properties of the asteroid. The calculations were performed for the full range of possible shape and spin-vector solutions derived from the available sample of visual lightcurve observations. Results. The near-Earth asteroid 162173 (1999 JU3) has an effective diameter of 0.87 +/- 0.03 km and a geometric albedo of 0.070 +/- 0.006. The chi(2)-test reveals a strong preference for a retrograde sense of rotation with a spin-axis orientation of lambda(ecl) = 73 degrees, beta(ecl) = -62 degrees and P-sid = 7.63 +/- 0.01 h. The most likely thermal inertia ranges between 200 and 600 Jm(-2) s(-0.5) K-1, about a factor of 2 lower than the value for 25143 Itokawa. This indicates that the surface lies somewhere between a thick-dust regolith and a rock/boulder/cm-sized, gravel-dominated surface like that of 25143 Itokawa. Our analysis represents the first time that shape and spin-vector information has been derived from a combined data set of visual lightcurves (reflected light) and mid-infrared photometry and spectroscopy (thermal emission).

We present the new method of detecting the asteroids quickly and automatically from a large volume of imaging data that are obtained by fully-depleted and undersampled CCD camera, by optimizing for a multi-core PC. The method detects the asteroids as faint as those detected by eyes *in much shorter time than eyes.

ISLE is a near-infrared imager and spectrograph for the Cassegrain focus (f/18) of the 1.88 m telescope at Okayama Astrophysical Observatory. It is upgraded instrument with a new detector, HAWAII-1 HgCdTe array and new optics. ISLE provides imaging capabilities which covers 4.2 x 4.2 arcmin(2) field-of-view at 0.25 aresec/pixel and long-slit (4 arcmin) spectroscopic capabilities at lambda/Delta lambda = 1000 - 4000 using reflection gratings. The noise performance of the detector is excellent. The read noise of 2.5 electrons with 25 Fowler pairs has been achieved, that is one of the world's lowest level among the instruments which use HAWAII-I array as the detector. We discuss the technical performance of ISLE and examine the upgrade effectiveness.

Sulfur dioxide (SO₂) absorbs ultraviolet (UV) radiation, and airborne spectrometers can measure its spatial distribution using backscattered solar light. A new algorithm was developed to estimate the SO₂ vertical column amount. This algorithm is based on the Differential Optical Absorption Spectroscopy (DOAS) technique and the radiative transfer calculation. Aircraft-borne measurements using a ultraviolet spectrometer, the Airborne-OPUS, were performed above Miyake-jima (34^&deg;N, 139.5^&deg;E) in January 2002. The amount of SO₂ estimated by the Airborne-OPUS was validated using SO₂ mixing ratios measured simultaneously by an onboard air-sampling sensor during the spiral-down flight above and inside volcanic plumes. The results suggested that the above algorithm is capable of quantifying the column amount of volcanic SO₂.

The Bisei Spaceguard Center started to observe space debris with special stress on space debris orbiting around geo-synchronous orbit using the 0.5m and 1.0m optical telescopes. We measured around ten thousand positions of objects and detected several satellites. In some number of images, several satellites were in our wide field and in some cases they were orbiting around each other. Through our survey observations, we detected several hundred objects, some of which are identified with catalogued objects, and the other of which can not be identified with those catalogued. Our limiting magnitudes are 16.5 to 18.0 magnitudes for both 0.5m and 1.0m telescopes, which are not so good as expected from those telescope specifications, and therefore both telescopes are still under improvement of those limiting magnitudes. The accuracies of position determination are under I arc second which is good enough to determine orbital elements of each object using 3 consecutive night data. We will review our results obtained in these 5 years.

ISLE is a near-infrared (1.0-2.5 mu m) imager and spectrograph for the Cassegrain focus (f/18) of the 1.88 m telescope at Okayama Astrophysical Observatory. The detector is a HAWAII 1024 X 1024 HgCdTe Array, which covers 4.2 x 4.2 arcmin(2) field of view with a pixel scale of 0.25 arcsec/pixel. ISLE also provides medium (R=300 - 4800) resolution long-slit (4 arcmin long) spectroscopic capabilities using reflection gratings. A dedicated front-end electronics for the detector achieved a readout noise of 8 electrons by the conventional Fowler sampling, and a operation scheme that combined with a number of discarded readout greatly suppressed the reset anomaly. The measured limiting magnitudes were J=18.6 and K=17.7 (imaging of point sources at S/N=10 for 10 min. exposure).

Medium-resolution (R similar to 500), K-band two-dimensional spectra are presented for the planetary nebula NGC 7027. The spatial distributions for the two bright unidentified lines near 2.199 and 2.287 p m were revealed and examined compared to those of other emission lines. It was spatially confirmed that the unidentified lines do not arise from neutral molecules, but ionized species. The ionization potentials of their parent ions are lower than that of He it, and comparable to or higher than that of Brgamma. Our results support the previous studies of identification of parent species, on the condition that the carriers of the unidentified lines are partly excited by collisions.

We have developed an air-borne ultraviolet remote sensor, named "Airborne-OPUS." It is a nadir-looking hyper spectral imaging spectrograph, with 1100 spectral channels and 330 spatial channels. It covers the wavelength range of 190-455 nm with 0.34 nm sampling step and covers 15 degrees field of view. All main components of the sensor are composed of commercially available products : a Jobin-Yvon spectrograph as a disperser, a PixelVision 1100&times;330 CCD camera as a detector, and a ready-made single lens as its front-end optics. For the data calibration, we examined the basic parameters and the performance characteristics of the detector, such as read noise, dark current, linearity, and pixel-response uniformity.<BR>After two-demonstration flights using the Gulfstream-II aircraft, the performances of Airborne-OPUS, such as spectral resolution, signal-to-noise ratio, have been evaluated. In the flights around Miyake-jima and Sakura-jima volcanoes, the absorption structure of SO₂ was detected in the observed spectra, using the DOAS technique. The vertical column amount of SO₂ was derived from each data, and its horizontal distribution was revealed. The sensitivity of the sensor was also examined, and we discussed its application to the detection of urban pollutions.

Air-OPUS is a hyper spectral imaging spectrograph, with 0.34 nm spectral step, 190-455 nm spectral coverage, and 330 spatial channels covering 15 degrees field of view (FOV). It is designed as an airborne instrument for the demonstration of spaceborne-OPUS. After two-demonstration campaign using the Gulfstream-II aircraft, the performances of Air-OPUS, such as spectral resolution, signal-to-noise ratio (SNR) have been evaluated. It is concluded, that the performances have agreed with designed value. This paper describes design, the performance, and the first results of Air-OPUS. Concept of next generation Air-OPUS, with wider FOV and visible/near-IR spectral coverage, will be also briefly presented.

We present a high-resolution (16") (CO)-C-13 (J = 1-0) map of the central region of W 51. We observed an area of about 15.'3 x 16.'7, which covers the entire region of G49.5-0.4, the brightest source in the W 51 region. Four discrete molecular clouds were identified toward G49.5-0.4, and evidence of cloud-cloud collisions was found. We speculate that a "pileup" of three molecular clouds resulted in a burst of massive star formation in G49.5-0.4.

Medium-resolution (R similar to 460) spectra in the K window have been obtained for the compact H II regions W51 IRS 2 East and IRS 2 West. Br gamma, He I, three lines of [Fe III], and seven lines of molecular hydrogen (H-2) have been detected. The unidentified line at 2.288 mum was also detected with similar to2% of the intensity of Br gamma. We derive an electron density of similar to 10(5)-10(6) cm(-3) in both IRS 2 East and IRS 2 West from [Fe III] line ratios. In both regions, observed line ratios indicate that the excitation of is H 2 H 2 dominated by fluorescence rather than by shocks.

Near-infrared observations of the central part of W51 have been carried out. We obtained J, H, and K' broadband and Bry narrowband imaging data over an area of 15 arcmin(2), centered near W51 IRS 2, which covers the whole of an H II region complex G49.5-0.4. K-band spectroscopic observations were also carried out for selected objects in this area. More than 7000 point sources were detected from our imaging data, and about 160 sources were identified as physically associated with G49.5-0.4. We estimated absolute J magnitude for each source from our photometric data and inferred the ages of H II regions from the sizes of nebulosities on our Bry image. Coupling information of the ages and the luminosities of exciting stars, we estimated their initial masses and the derived initial mass function (IMF) of massive stars in G49.5-0.4. In the mass range between 10 and 30 M. the IMF slope is consistent with the value 1.8, which is derived for field stars. However, there is an excess of stellar population in the range above 30 M.; i.e., a top heavy-shaped IMF was derived. We defined four subgroups which are aligned parallel to the Galactic plane. The age of the oldest group was estimated to be 2.3 Myr and that of the youngest group to be younger than 1 Myr. The youngest group contains 22 O stars, and it seems that 17 out of 22 O stars were born in the last 0.8 Myr. The massive star formation activity of this group is more violent than any other visible Galactic H II region.