PUBLICATIONS


Notes

Please cite the following paper when you refer to Tomo-e Gozen in publications.

Sako, S. et al. 2018, "The Tomo-e Gozen wide field CMOS camera for the Kiso Schmidt telescope", Proceedings of the SPIE, Volume 10702, id. 107020J 17 pp. (2018), DOI:10.1117/12.2310049


Papers referring to Tomo-e Gozen

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Papers written by Tomo-e Gozen collaboration members

  1. J-GEM optical and near-infrared follow-up of gravitational wave events during LIGO's and Virgo's third observing run
    Date
    May 2021
    Article
    Progress of Theoretical and Experimental Physics, Volume 2021, Issue 5, id.05A104, 23 pp. 10.1093/ptep/ptab007
    Authors
    Sasada, Mahito ; Utsumi, Yousuke ; Itoh, Ryosuke ; Tominaga, Nozomu ; Tanaka, Masaomi ; Morokuma, Tomoki ; Yanagisawa, Kenshi ; Kawabata, Koji S. ; Ohgami, Takayuki ; Yoshida, Michitoshi ; Abe, Fumio ; Adachi, Ryo ; Akitaya, Hiroshi ; Chong, Yang ; Daikuhara, Kazuki ; Hamasaki, Ryo ; Honda, Satoshi ; Hosokawa, Ryohei ; Iida, Kota ; Imazato, Fumiya Ishioka, Chihiro ; Iwasaki, Takumi ; Jian, Mingjie ; Kamei, Yuhei ; Kanai, Takahiro ; Kaneda, Hidehiro ; Kaneko, Ayane ; Katoh, Noriyuki ; Kawai, Nobuyuki ; Kubota, Keiichiro ; Kubota, Yuma ; Mamiya, Hideo ; Matsubayashi, Kazuya ; Morihana, Kumiko ; Murata, Katsuhiro L. ; Nagayama, Takahiro ; Nakamura, Noriatsu ; Nakaoka, Tatsuya ; Niino, Yuu ; Nishinaka, Yuki ; Niwano, Masafumi ; Nogami, Daisaku ; Oasa, Yumiko ; Oeda, Miki ; Ogawa, Futa ; Ohsawa, Ryou ; Ohta, Kouji ; Oide, Kohei ; Onozato, Hiroki ; Sako, Shigeyuki ; Saito, Tomoki ; Sekiguchi, Yuichiro ; Shigeyama, Toshikazu ; Shigeyoshi, Takumi ; Shikauchi, Minori ; Shiraishi, Kazuki ; Suzuki, Daisuke ; Takagi, Kengo ; Takahashi, Jun ; Takarada, Takuya ; Takayama, Masaki ; Takeuchi, Himeka ; Tamura, Yasuki ; Tanaka, Ryoya ; Toma, Sayaka ; Tozuka, Miyako ; Uchida, Nagomi ; Uzawa, Yoshinori ; Yamanaka, Masayuki ; Yasuda, Moeno ; Yatsu, Yoichi
    Abstract

    The Laser Interferometer Gravitational-wave Observatory Scientific Collaboration and Virgo Collaboration (LVC) sent out 56 gravitational-wave (GW) notices during the third observing run (O3). The Japanese Collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM) performed optical and near-infrared observations to identify and observe an electromagnetic (EM) counterpart. We constructed a web-based system that enabled us to obtain and share information on candidate host galaxies for the counterpart, and the status of our observations. Candidate host galaxies were selected from the GLADE catalog with a weight based on the 3D GW localization map provided by LVC. We conducted galaxy-targeted and wide-field blind surveys, real-time data analysis, and visual inspection of observed galaxies. We performed galaxy-targeted follow-ups to 23 GW events during O3, and the maximum probability covered by our observations reached 9.8%. Among these, we successfully started observations for 10 GW events within 0.5 days after the detection. This result demonstrates that our follow-up observation has the potential to constrain EM radiation models for a merger of binary neutron stars at a distance of up to ∼100 Mpc with a probability area of ≤ 500 deg2.

  2. Calcium-rich Transient SN 2019ehk in a Star-forming Environment: Yet Another Candidate for a Precursor of a Double Neutron-star Binary
    Date
    May 2021
    Article
    The Astrophysical Journal, Volume 912, Issue 1, id.30, 14 pp. 10.3847/1538-4357/abe765
    Authors
    Nakaoka, Tatsuya ; Maeda, Keiichi search by orcid ; Yamanaka, Masayuki search by orcid ; Tanaka, Masaomi search by orcid ; Kawabata, Miho search by orcid ; Moriya, Takashi J. search by orcid ; Kawabata, Koji S. ; Tominaga, Nozomu search by orcid ; Takagi, Kengo ; Imazato, Fumiya ; Morokuma, Tomoki search by orcid ; Sako, Shigeyuki ; Ohsawa, Ryou search by orcid ; Nagao, Takashi search by orcid ; Jiang, Ji-an search by orcid ; Burgaz, Umut ; Taguchi, Kenta ; Uemura, Makoto ; Akitaya, Hiroshi search by orcid ; Sasada, Mahito search by orcid Isogai, Keisuke ; Otsuka, Masaaki ; Maehara, Hiroyuki
    Abstract

    We present optical and near-infrared observations of SN 2019ehk, which was initially reported as a Type Ib supernova (SN). We show that it evolved to a Ca-rich transient according to its spectral properties and evolution in late phases. However, it shows a few properties distinct from those of the canonical Ca-rich transients: a short-duration first peak in the light curve, high peak luminosity, and association with a star-forming environment. Indeed, some of these features are shared with iPTF14gqr and iPTF16hgs, which are candidates for a special class of core-collapse SNe: the so-called ultra-stripped envelope SNe, i.e., a relatively low-mass He (or C+O) star explosion in a binary as a precursor of short-period double neutron star (NS) binaries. The estimated ejecta mass (0.4M⊙) and explosion energy (1.7 × 1050 erg) are consistent with this scenario. The analysis of the first peak suggests the existence of dense circumstellar material in the vicinity of the progenitor, implying a CCSN origin. Based on this analysis, we suggest SN 2019ehk is another candidate for a low-mass He star explosion. It might create a double NS binary, but with a wide separation. These candidates for low-mass stripped envelope SNe, including ultra-stripped envelope SN candidates, seem to form a subpopulation among Ca-rich transients, associated with young population. We propose that the key to distinguishing this population is the early first peak in their light curves.

  3. ASASSN-18aan: An eclipsing SU UMa-type cataclysmic variable with a 3.6-hr orbital period and a late G-type secondary star
    Date
    February 2021
    Article
    Publications of the Astronomical Society of Japan, Advance Access 10.1093/pasj/psab003
    Authors
    Wakamatsu, Yasuyuki ; Thorstensen, John R. ; Kojiguchi, Naoto ; Isogai, Keisuke ; Kimura, Mariko ; Ohnishi, Ryuhei ; Kato, Taichi ; Itoh, Hiroshi ; Sugiura, Yuki ; Sumiya, Sho ; Matsumoto, Hanami ; Ito, Daiki ; Nikai, Kengo ; Akitaya, Hiroshi ; Ishioka, Chihiro ; Oide, Kohei ; Kanai, Takahiro ; Uzawa, Yoshinori ; Oasa, Yumiko ; Tordai, Tamás Vanmunster, Tonny ; Shugarov, Sergey Yu ; Yamanaka, Masayuki ; Sasada, Mahito ; Takagi, Kengo ; Nishinaka, Yuki ; Yamazaki, Yuina ; Otsubo, Ikki ; Nakaoka, Tatsuya ; Murata, Katsuhiro L. ; Ohsawa, Ryou ; Morita, Masahiro ; Ichiki, Makoto ; Dufoer, Sjoerd ; Mizutani, Masanori ; Horiuchi, Takashi ; Tozuka, Miyako ; Takayama, Masaki ; Ohshima, Tomohito ; Saito, Tomoki ; Dubovsky, Pavol A. ; Stone, Geoff ; Miller, Ian ; Nogami, Daisaku
    Abstract

    We report photometric and spectroscopic observations of the eclipsing SU UMa-type dwarf nova ASASSN-18aan. We observed the 2018 superoutburst with 2.3 mag brightening and found the orbital period (Porb) to be 0.149454(3) d, or 3.59 hr. This is longward of the period gap, establishing ASASSN-18aan as one of a small number of long-Porb SU UMa-type dwarf novae. The estimated mass ratio, [q = M2/M1 = 0.278(1)], is almost identical to the upper limit of tidal instability by the 3 : 1 resonance. From eclipses, we found that the accretion disk at the onset of the superoutburst may reach the 3 : 1 resonance radius, suggesting that the superoutburst of ASASSN-18aan results from the tidal instability. Considering the case of long-Porb WZ Sge-type dwarf novae, we suggest that the tidal dissipation at the tidal truncation radius is enough to induce SU UMa-like behavior in relatively high-q systems such as SU UMa-type dwarf novae, but that this is no longer effective in low-q systems such as WZ Sge-type dwarf novae. The unusual nature of the system extends to the secondary star, for which we find a spectral type of G9, much earlier than typical for the orbital period, and a secondary mass M2 of around 0.18 M⊙, smaller than expected for the orbital period and the secondary's spectral type. We also see indications of enhanced sodium abundance in the secondary's spectrum. Anomalously hot secondaries are seen in a modest number of other CVs and related objects. These systems evidently underwent significant nuclear evolution before the onset of mass transfer. In the case of ASASSN-18aan, this apparently resulted in a mass ratio lower than typically found at the system's Porb, which may account for the occurrence of a superoutburst at this relatively long period.

  4. Follow-up observations for IceCube-170922A: Detection of rapid near-infrared variability and intensive monitoring of TXS 0506+056
    Date
    February 2021
    Article
    Publications of the Astronomical Society of Japan, Volume 73, Issue 1, pp.25-43 10.1093/pasj/psaa110
    Authors
    Morokuma, Tomoki; Utsumi, Yousuke; Ohta, Kouji; Yamanaka, Masayuki; Kawabata, Koji S.; Inoue, Yoshiyuki; Tanaka, Masaomi; Yoshida, Michitoshi; Itoh, Ryosuke; Sasada, Mahito; Tominaga, Nozomu; Mori, Hiroki; Kawabata, Miho; Nakaoka, Tatsuya; Chogi, Maiko; Abe, Taisei; Huang, Ruochen; Kawahara, Naoki; Kimura, Hiroki; Nagashima, Hiroki Takagi, Kengo; Yamazaki, Yuina; Liu, Wei; Ohsawa, Ryou; Sako, Shigeyuki; Murata, Katsuhiro L.; Morihana, Kumiko; Gilligan, Christina K.; Isogai, Keisuke; Kimura, Mariko; Wakamatsu, Yasuyuki; Ohnishi, Ryuhei; Takayama, Masaki; Honda, Satoshi; Matsuoka, Yoshiki; Yamashita, Takuji; Nagataki, Shigehiro; Tanaka, Yasuyuki T. Ohsawa, Ryou; Hirota, Akira; Morita, Kohei; Abe, Shinsuke; Kastinen, Daniel; Kero, Johan; Szasz, Csilla; Fujiwara, Yasunori; Nakamura, Takuji; Nishimura, Koji; Sako, Shigeyuki; Watanabe, Jun-ichi; Aoki, Tsutomu; Arima, Noriaki; Arimatsu, Ko; Doi, Mamoru; Ichiki, Makoto; Ikeda, Shiro; Ita, Yoshifusa; Kasuga, Toshihiro Kobayashi, Naoto; Kokubo, Mitsuru; Konishi, Masahiro; Maehara, Hiroyuki; Miyata, Takashi; Mori, Yuki; Morii, Mikio; Morokuma, Tomoki; Motohara, Kentaro; Nakada, Yoshikazu; Okumura, Shin-ichiro; Sarugaku, Yuki; Sato, Mikiya; Shigeyama, Toshikazu; Soyano, Takao; Takahashi, Hidenori; Tanaka, Masaomi; Tarusawa, Ken'ichi; Tominaga, Nozomu; Urakawa, Seitaro; Usui, Fumihiko; Yamashita, Takuya; Yoshikawa, Makoto
    Abstract

    We present our follow-up observations to search for an electromagnetic counterpart of the IceCube high-energy neutrino IceCube-170922A. Monitoring observations of a likely counterpart, TXS 0506+056, are also described. First, we quickly took optical and near-infrared images of seven flat-spectrum radio sources within the IceCube error region right after the neutrino detection and found a rapid flux decline of TXS 0506+056 in Kanata/HONIR J-band data. Motivated by this discovery, intensive follow-up observations of TXS 0506+056 were continuously performed, including our monitoring imaging observations, spectroscopic observations, and polarimetric observations in optical and near-infrared wavelengths. TXS 0506+056 showed a large-amplitude (∼1.0 mag) variability in a time scale of several days or longer, although no significant variability was detected in a time scale of a day or shorter. TXS 0506+056 also showed a bluer-when-brighter trend in optical and near-infrared wavelengths. Structure functions of the variabilities were examined and indicate that TXS 0506+056 is not a special blazar in terms of optical variability. Polarization measurement results of TXS 0506+056 are also discussed.

  5. Relationship between radar cross section and optical magnitude based on radar and optical simultaneous observations of faint meteors
    Date
    December 2020
    Article
    Planetary and Space Science, Volume 194, article id. 105011, 10.1016/j.pss.2020.105011
    Authors
    Ohsawa, Ryou; Hirota, Akira; Morita, Kohei; Abe, Shinsuke; Kastinen, Daniel; Kero, Johan; Szasz, Csilla; Fujiwara, Yasunori; Nakamura, Takuji; Nishimura, Koji; Sako, Shigeyuki; Watanabe, Jun-ichi; Aoki, Tsutomu; Arima, Noriaki; Arimatsu, Ko; Doi, Mamoru; Ichiki, Makoto; Ikeda, Shiro; Ita, Yoshifusa; Kasuga, Toshihiro Kobayashi, Naoto; Kokubo, Mitsuru; Konishi, Masahiro; Maehara, Hiroyuki; Miyata, Takashi; Mori, Yuki; Morii, Mikio; Morokuma, Tomoki; Motohara, Kentaro; Nakada, Yoshikazu; Okumura, Shin-ichiro; Sarugaku, Yuki; Sato, Mikiya; Shigeyama, Toshikazu; Soyano, Takao; Takahashi, Hidenori; Tanaka, Masaomi; Tarusawa, Ken'ichi; Tominaga, Nozomu; Urakawa, Seitaro; Usui, Fumihiko; Yamashita, Takuya; Yoshikawa, Makoto
    Abstract

    Radar and optical simultaneous observations of meteors are important to understand the size distribution of the interplanetary dust. However, faint meteors detected by high power large aperture radar observations, which are typically as faint as 10 mag. In optical, have not been detected until recently in optical observations, mainly due to insufficient sensitivity of the optical observations. In this paper, two radar and optical simultaneous observations were organized. The first observation was carried out in 2009-2010 using Middle and Upper Atmosphere Radar (MU radar) and an image-intensified CCD camera. The second observation was carried out in 2018 using the MU radar and a mosaic CMOS camera, Tomo-e Gozen, mounted on the 1.05-m Kiso Schmidt Telescope. In total, 331 simultaneous meteors were detected. The relationship between radar cross sections and optical V-band magnitudes was well approximated by a linear function. A transformation function from the radar cross section to the V-band magnitude was derived for sporadic meteors. The transformation function was applied to about 150,000 meteors detected by the MU radar in 2009-2015, large part of which are sporadic, and a luminosity function was derived in the magnitude range of -1.5-9.5 mag. The luminosity function was well approximated by a single power-law function with the population index of r = 3.52 ± 0.12 . The present observation indicates that the MU radar has capability to detect interplanetary dust of 10-5 -100g in mass as meteors.

  6. Phase curves of >40,000 small solar system bodies obtained by the Tomo-e Gozen transient survey
    Date
    October 2020
    Article
    AAS Division of Planetary Science meeting #52, id. 208.06. Bulletin of the American Astronomical Society, Vol. 52, No. 6 e-id 2020n6i208p06
    Authors
    Yoshida, F.; Ito, T.; Urakawa, S.; Terai, T.; Tominaga, N.; Morokuma, T.; Sako, S.; Ohsawa, R.; Tanaka, M.; Hamasaki, R.; Tomo-e Gozen Collaboration
    Abstract

    The Tomo-e Gozen project conducts optical wide-field survey programs with a wide-field CMOS camera, Tomo-e Gozen, attached on the 105-cm Schmidt telescope at the Kiso Observatory, the University of Tokyo. Tomo-e Gozen is the world's first wide-field CMOS camera which covers 20 square degrees with 84 chips of 35 mm full HD CMOS image sensors. A wide-field and high-cadence survey in the optical wavelengths began in 2018 with the Tomo-e Gozen (hereafter referred to as the Tomo-e Gozen transient survey). The main purpose of this survey is to detect young supernovae. However, the survey simultaneously detects a large number of moving objects in their images. As one of the by-products of the survey, here we show our preliminary result about production of phase curves (solar phase angles versus absolute magnitude) of more than 40,000 (as of April 11, 2020) small solar system bodies including main-belt asteroids, near-Earth asteroids, Jupiter Trojans, Centaurs, and Transneptunian objects. Combining the moving object catalogue derived from the survey and the output ephemeris that the Horizons/JPL system provides, we are now able to obtain phase curves of these objects almost automatically. As the Kiso moving object catalogue is updated and being expanded on a daily basis, the number of the objects (small bodies) that we deal with goes up as well. Our result, when completed, will make a fair complement as well as a significant keystone to what is already published such as from the Pan-STARRS systematic survey on the knowledge of the surface characteristics of the small solar system bodies.

  7. No optical bursts detected from SGR J1935+2154 by 24 fps observations with Tomo-e Gozen
    Date
    May 2020
    Article
    GRB Coordinates Network, Circular Service, No. 27678, link
    Authors
    Niino, Y.; Morokuma, T.; Sako, S.; Ohsawa, R.; Beniyama, J.; Kokubo, M.; Tomo-e Gozen Collaboration
    Abstract

    We performed monitoring observations of SGR J1935+2154, from which intense burst activities have been found in the last few days (GCN #27657, #27659, #27661, #27663, #27664, #27665, #27667, #27668, #27669, #27675, ATel #13675, #13678, #13679, #13681, #13682, #13684, #13685, #13686, #13687, #13688, #13692, #13693, #13697), for 7 hrs (3.5 hrs starting UTC 2020-04-30 15:28 + 3.5 hrs starting UTC 2020-05-01 15:28) using the Tomo-e Gozen camera (optical CMOS imager, Sako et al. 2018, SPIE, 10702, 107020J) mounted on the 105-cm Kiso Schmidt telescope. The observations were conducted in a high-speed imaging mode with a frame rate of 24.4 fps (time resolution ~ 0.041 sec) and a 4.8x8 arcmin^2 FoV. Our quicklook analysis which degrades S/N of images by a factor of ~ 10 shows no apparent optical bursts above a 5-sigma limit of ~ 1 Jy ms.

  8. An optical search for transients lasting a few seconds
    Date
    February 2020
    Article
    Publications of the Astronomical Society of Japan, Volume 72, Issue 1, id.3, 10.1093/pasj/psz120
    Authors
    Richmond, Michael W.; Tanaka, Masaomi; Morokuma, Tomoki; Sako, Shigeyuki; Ohsawa, Ryou; Arima, Noriaki; Tominaga, Nozomu; Doi, Mamoru; Aoki, Tsutomu; Arimatsu, Ko; Ichiki, Makoto; Ikeda, Shiro; Ita, Yoshifusa; Kasuga, Toshihiro; Kawabata, Koji S.; Kawakita, Hideyo; Kobayashi, Naoto; Kokubo, Mitsuru; Konishi, Masahiro; Maehara, Hiroyuki Mito, Hiroyuki; Miyata, Takashi; Mori, Yuki; Morii, Mikio; Motohara, Kentaro; Nakada, Yoshikazu; Okumura, Shin-Ichiro; Onozato, Hiroki; Sarugaku, Yuki; Sato, Mikiya; Shigeyama, Toshikazu; Soyano, Takao; Takahashi, Hidenori; Tanikawa, Ataru; Tarusawa, Ken'ichi; Urakawa, Seitaro; Usui, Fumihiko; Watanabe, Junichi; Yamashita, Takuya; Yoshikawa, Makoto
    Abstract

    Using a prototype of the Tomo-e Gozen wide-field CMOS mosaic camera, we acquire wide-field optical images at a cadence of 2Hz and search them for transient sources of duration 1.5 to 11.5s. 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.

  9. New Constraint on the Atmosphere of (50000) Quaoar from a Stellar Occultation
    Date
    December 2019
    Article
    The Astronomical Journal, Volume 158, Issue 6, article id. 236, 7 pp. (2019), 10.3847/1538-3881/ab5058
    Authors
    Arimatsu, Ko; Ohsawa, Ryou; Hashimoto, George L.; Urakawa, Seitaro; Takahashi, Jun; Tozuka, Miyako; Itoh, Yoichi; Yamashita, Misato; Usui, Fumihiko; Aoki, Tsutomu; Arima, Noriaki; Doi, Mamoru; Ichiki, Makoto; Ikeda, Shiro; Ita, Yoshifusa; Kasuga, Toshihiro; Kobayashi, Naoto; Kokubo, Mitsuru; Konishi, Masahiro; Maehara, Hiroyuki Matsunaga, Noriyuki; Miyata, Takashi; Morii, Mikio; Morokuma, Tomoki; Motohara, Kentaro; Nakada, Yoshikazu; Okumura, Shin-ichiro; Sako, Shigeyuki; Sarugaku, Yuki; Sato, Mikiya; Shigeyama, Toshikazu; Soyano, Takao; Takahashi, Hidenori; Tarusawa, Ken'ichi; Tominaga, Nozomu; Watanabe, Jun-ichi; Yamashita, Takuya; Yoshikawa, Makoto
    Abstract

    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 1σ and 3σ 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.

  10. LIGO/Virgo S190930t: Upper limits on the two of the ZTF/GROWTH candidates
    Date
    October 2019
    Article
    GRB Coordinates Network, Circular Service, No. 25907, link
    Authors
    Morokuma, T.; Utsumi, Y.; J-GEM Collaboration
    Abstract

    We report optical follow-up imaging observations for the electromagnetic counterpart candidates of the gravitational wave event S190930t (The LIGO Scientific Collaboration and the Virgo Collaboration, GCN Circ. 25876) reported by Stein et al. (GCN Circ. 25899). We took 12 contiguous frames of 0.5-second exposures 19-22 hours from the possible neutron star and black hole merger for the regions around ZTF19acbpqlh (AT2019rpn) and ATLAS19wyn (AT2019rpj) with Tomo-e Gozen (Sako et al. 2018, SPIE, 10702, 107020J) on the 1.05-m Kiso Schmidt telescope. No filters are used and the data are calibrated relative to r-band data from Pan-STARRS DR2. We find no transients at the reported locations down to depths in the AB system shown below. | MJD | AT | depth (5 sigmas) | | 58757.40871 | ZTF19acbpqlh (AT2019rpn) | 18.69 | | 58757.51431 | ZTF19acbpqlh (AT2019rpn) | 17.66 | | 58757.43221 | ATLAS19wyn (AT2019rpj) | 18.53 | | 58757.52506 | ATLAS19wyn (AT2019rpj) | 18.04 | We note that the ZTF/GROWTH reported magnitudes are 1.0-2.4 magnitudes fainter than our detection limits above.

  11. Shape and Rotational Motion Models for Tumbling and Monolithic Asteroid 2012 TC4: High Time Resolution Light Curve with the Tomo-e Gozen Camera
    Date
    April 2019
    Article
    The Astronomical Journal, Volume 157, Issue 4, article id. 155, 13 pp. (2019), 10.3847/1538-3881/ab09f0
    Authors
    Urakawa, Seitaro; Ohsawa, Ryou; Sako, Shigeyuki; Okumura, Shin-ichiro; Sakurai, Yuri; Takahashi, Jun; Imamura, Kazuyoshi; Naito, Hiroyuki; Watanabe, Fumitake; Nagayoshi, Ryoma; Murakami, Yasuhiko; Okazaki, Ryo; Sekiguchi, Tomohiko; Ishiguro, Masateru; Michikami, Tatsuhiro; Yoshikawa, Makoto
    Abstract

    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 × 8.0 × 14.9 m or 3.3 × 8.0 × 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 ∼3 × 105 yr and 2012 TC4 has a fresh surface.

  12. Luminosity function of faint sporadic meteors measured with a wide-field CMOS mosaic camera Tomo-e PM
    Date
    January 2019
    Article
    Planetary and Space Science, Volume 165, p. 281-292 (2019), 10.1016/j.pss.2018.09.006
    Authors
    Ohsawa, Ryou; Sako, Shigeyuki; Sarugaku, Yuki; Usui, Fumihiko; Ootsubo, Takafumi; Fujiwara, Yasunori; Sato, Mikiya; Kasuga, Toshihiro; Arimatsu, Ko; Watanabe, Jun-ichi; Doi, Mamoru; Kobayashi, Naoto; Takahashi, Hidenori; Motohara, Kentaro; Morokuma, Tomoki; Konishi, Masahiro; Aoki, Tsutomu; Soyano, Takao; Tarusawa, Ken'ichi; Mori, Yuki Nakada, Yoshikazu; Ichiki, Makoto; Arima, Noriaki; Kojima, Yuto; Morita, Masahiro; Shigeyama, Toshikazu; Ita, Yoshifusa; Kokubo, Mitsuru; Mitsuda, Kazuma; Maehara, Hiroyuki; Tominaga, Nozomu; Yamashita, Takuya; Ikeda, Shiro; Morii, Mikio; Urakawa, Seitaro; Okumura, Shin-ichiro; Yoshikawa, Makoto
    Abstract

    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.

  13. LIGO/Virgo S190426c: J-GEM optical/NIR follow-up observations
    Date
    July 2018
    Article
    GRB Coordinates Network, Circular Service, No. 24299, #1 (2019/April-0), link
    Authors
    Niino, Y.; Morokuma, T.; Ohsawa, R.; Sako, S.; Shikauchi, M.; Yanagisawa, K.; Takagi, K.; Nakaoka, T.; Sasada, M.; Saito, T.; Itoh, R.; Ohta, K.; Utsumi, Y.; Sekiguchi, Y.; Tominaga, N.
  14. Evaluation of large pixel CMOS image sensors for the Tomo-e Gozen wide field camera
    Date
    July 2018
    Article
    Proceedings of the SPIE, Volume 10709, id. 107091T 10 pp. (2018), 10.1117/12.2311301
    Authors
    Kojima, Yuto; Sako, Shigeyuki; Ohsawa, Ryou; Takahashi, Hidenori; Doi, Mamoru; Kobayashi, Naoto; Aoki, Tsutomu; Arima, Noriaki; Arimatsu, Ko; Ichiki, Makoto; Ikeda, Shiro; Inooka, Kota; Ita, Yoshifusa; Kasuga, Toshihiro; Kokubo, Mitsuru; Konishi, Masahiro; Maehara, Hiroyuki; Matsunaga, Noriyuki; Mitsuda, Kazuma; Miyata, Takashi Mori, Yuki; Morii, Mikio; Morokuma, Tomoki; Motohara, Kentaro; Nakada, Yoshikazu; Okumura, Shin-Ichiro; Sarugaku, Yuki; Sato, Mikiya; Shigeyama, Toshikazu; Soyano, Takao; Tanaka, Masaomi; Tarusawa, Ken'ichi; Tominaga, Nozomu; Totani, Tomonori; Urakawa, Seitaro; Usui, Fumihiko; Watanabe, Junichi; Yamashita, Takuya; Yoshikawa, Makoto
    Abstract

    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.

  15. The Tomo-e Gozen wide field CMOS camera for the Kiso Schmidt telescope
    Date
    July 2018
    Article
    Proceedings of the SPIE, Volume 10702, id. 107020J 17 pp. (2018), 10.1117/12.2310049
    Authors
    Sako, Shigeyuki; Ohsawa, Ryou; Takahashi, Hidenori; Kojima, Yuto; Doi, Mamoru; Kobayashi, Naoto; Aoki, Tsutomu; Arima, Noriaki; Arimatsu, Ko; Ichiki, Makoto; Ikeda, Shiro; Inooka, Kota; Ita, Yoshifusa; Kasuga, Toshihiro; Kokubo, Mitsuru; Konishi, Masahiro; Maehara, Hiroyuki; Matsunaga, Noriyuki; Mitsuda, Kazuma; Miyata, Takashi Mori, Yuki; Morii, Mikio; Morokuma, Tomoki; Motohara, Kentaro; Nakada, Yoshikazu; Okumura, Shin-Ichiro; Sarugaku, Yuki; Sato, Mikiya; Shigeyama, Toshikazu; Soyano, Takao; Tanaka, Masaomi; Tarusawa, Ken'ichi; Tominaga, Nozomu; Totani, Tomonori; Urakawa, Seitaro; Usui, Fumihiko; Watanabe, Junichi; Yamashita, Takuya; Yoshikawa, Makoto
    Abstract

    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.

  16. Detection of 10-msec scale optical flares in the black-hole binary candidate MAXI J1820+070 (ASASSN-18ey)
    Date
    March 2018
    Article
    The Astronomer's Telegram, No. 11426, link
    Authors
    Sako, S.; Ohsawa, R.; Ichiki, M.; Maehara, H.; Morii, M.; Tanaka, M.
  17. Data Compression for the Tomo-e Gozen Using Low-rank Matrix Approximation
    Date
    January 2017
    Article
    The Astrophysical Journal, Volume 835, Issue 1, article id. 1, 5 pp. (2017), 10.3847/1538-4357/835/1/1
    Authors
    Morii, M., Ikeda, S., Sako, S., Ohsawa, R.
    Abstract

    Optical wide-field surveys with a high cadence are expected to create a new field of astronomy, so-called “movie astronomy,” in the near future. The amount of data from the observations will be huge, and hence efficient data compression will be indispensable. Here we propose a low-rank matrix approximation with sparse matrix decomposition as a promising solution to reduce the data size effectively while preserving sufficient scientific information. We apply one of the methods to the movie data obtained with the prototype model of the Tomo-e Gozen mounted on the 1.0 m Schmidt telescope of Kiso Observatory. Once full-scale observation with the Tomo-e Gozen commences, it will generate ̃30 TB of data per night. We demonstrate that the data are compressed by a factor of about 10 in size without losing transient events like optical short transient point sources and meteors. The intensity of point sources can be recovered from the compressed data. The processing runs sufficiently fast, compared with the expected data-acquisition rate in the actual observing runs.

  18. Development of a real-time data processing system for a prototype of the Tomo-e Gozen wide field CMOS camera
    Date
    August 2016
    Article
    Proceedings of the SPIE, Volume 9913, id. 991339 8 pp. (2016), 10.1117/12.2231615
    Authors
    Ohsawa, Ryou; Sako, Shigeyuki; Takahashi, Hidenori; Kikuchi, Yuki; Doi, Mamoru; Kobayashi, Naoto; Aoki, Tsutomu; Arimatsu, Ko; Ichiki, Makoto; Ikeda, Shiro; Ita, Yoshifusa; Kasuga, Toshihiro; Kawakita, Hideo; Kokubo, Mitsuru; Maehara, Hiroyuki; Matsunaga, Noriyuki; Mito, Hiroyuki; Mitsuda, Kazuma; Miyata, Takashi; Mori, Kiyoshi Mori, Yuki; Morii, Mikio; Morokuma, Tomoki; Motohara, Kentaro; Nakada, Yoshikazu; Okumura, Shin-ichiro; Onozato, Hiroki; Osawa, Kentaro; Sarugaku, Yuki; Sato, Mikiya; Shigeyama, Toshikazu; Soyano, Takao; Tanaka, Masaomi; Taniguchi, Yuki; Tanikawa, Ataru; Tarusawa, Ken'ichi; Tominaga, Nozomu; Totani, Tomonori; Urakawa, Seitaro; Usui, Fumihiko; Watanabe, Junichi; Yamaguchi, Jumpei; Yoshikawa, Makoto
    Abstract

    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.

  19. Development of a prototype of the Tomo-e Gozen wide-field CMOS camera
    Date
    August 2016
    Article
    Proceedings of the SPIE, Volume 9908, id. 99083P 15 pp. (2016), 10.1117/12.2231259
    Authors
    Sako, Shigeyuki; Osawa, Ryou; Takahashi, Hidenori; Kikuchi, Yuki; Doi, Mamoru; Kobayashi, Naoto; Aoki, Tsutomu; Arimatsu, Ko; Ichiki, Makoto; Ikeda, Shiro; Ita, Yoshifusa; Kasuga, Toshihiro; Kawakita, Hideyo; Kokubo, Mitsuru; Maehara, Hiroyuki; Matsunaga, Noriyuki; Mito, Hiroyuki; Mitsuda, Kazuma; Miyata, Takashi; Mori, Kiyoshi Mori, Yuki; Morii, Mikio; Morokuma, Tomoki; Motohara, Kentaro; Nakada, Yoshikazu; Osawa, Kentaro; Okumura, Shin-ichiro; Onozato, Hiroki; Sarugaku, Yuki; Sato, Mikiya; Shigeyama, Toshikazu; Soyano, Takao; Tanaka, Masaomi; Taniguchi, Yuki; Tanikawa, Ataru; Tarusawa, Ken'ichi; Tominaga, Nozomu; Totani, Tomonori; Urakawa, Seitaro; Usui, Fumihiko; Watanabe, Junichi; Yamaguchi, Jumpei; Yoshikawa, Makoto
    Abstract

    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 deg2 and a sub-second time-resolution, which are achieved by 84 chips of 2k×1k CMOS sensor. This camera adopts unconventional designs including a lightweight structure, a nonvacuumed 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 deg2. 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.

  20. Development of a prototype of the Tomo-e Gozen wide-field CMOS camera
    Date
    July 2016
    Article
    41st COSPAR Scientific Assembly, abstracts from the meeting that was to be held 30 July - 7 August at the Istanbul Congress Center (ICC), Turkey, but was cancelled. See http://cospar2016.tubitak.gov.tr/en/, Abstract id. B0.4-77-16.
    Authors
    Watanabe, Juniichi; Yoshikawa, Makoto; Urakawa, Seitaro; Usui, Fumihiko; Ohsawa, Ryou; Sako, Shigeyuki; Arimatsu, Ko
    Abstract

    We are developing an ultra wide-field fast camera, Tomo-e Gozen, which will be set up on the 105cm (F3.1) Schmidt telescope in Kiso Observatory at the University of Tokyo. Tomo-e equipped with 84 CMOS image sensors, which work in a room temperature, has a 20 square degree field of view and a fast readout speed of ~2 Hz. The purpose of this camera is the observation of the transient objects such as the counterpart of the gravitational wave events, the ultra wide-field capability with a high survey efficiency is also useful for small solar system bodies; NEOs, occultation events of the TNOs, and meteors. In the presentation, the specifications of Tomo-e are shown together with some preliminary results of the experimental observation run.

  21. GRB 151205C: Optical follow-up observations at Kiso
    Date
    December 2015
    Article
    The Astronomer's Telegram, No.8394, link
    Authors
    Kikuchi, Yuki; Tanaka, Masaomi; Ohsawa, Ryou; Ichiki, Makoto; Sako, Shigeyuki; Morokuma, Tomoki; Doi, Mamoru; Tominaga, Nozomu; Serino, Motoko; Suzuki, Akihiro; Maeda, Keiichi; Sakamoto, Takanori
  22. GRB 151205C: Optical follow-up observations at Kiso
    Date
    December 2015
    Article
    GRB Coordinates Network, Circular Service, No. 18677, #1 (2015), link
    Authors
    Kikuchi, Y.; Tanaka, M.; Ohsawa, R.; Ichiki, M.; Sako, S.; Morokuma, T.; Doi, M.; Tominaga, N.; Serino, M.; Suzuki, A.; Maeda, K.; Sakamoto, T.
  23. Faint meteor observation by large-format CMOS sensor with 1.05-m Kiso schmidt telescope
    Date
    July 2014
    Article
    The Meteoroids 2013, Proceedings of the Astronomical Conference held at A.M. University, Poznań, Poland, Aug. 26-30, 2013, Eds.: T.J. Jopek, F.J.M. Rietmeijer, J. Watanabe, I.P. Williams, A.M. University Press, 2014, p. 325-328
    Authors
    Watanabe, J.; Kasuga, T.; Terai, T.; Miyazaki, S.; Ohta, K.; Murooka, F.; Ohnishi, T.; Yamasaki, T.; Mito, H.; Aoki, T.; Soyano, T.; Tarusawa, K.; Matsunaga, N.; Sako, S.; Kobayashi, N.; Doi, M.; Enomoto, T.
    Abstract

    We tried to use a new high-sensitivity CMOS sensor of the world's largest size as a one-chip 20cmx 20cm square attached to the prime focus of the 1.05 m (F3.1) Schmidt telescope at the Kiso Observatory, University of Tokyo, for faint meteor observation. The resulting field of view was 3.3 by 3.3 degrees, with a limiting magnitude of about 12 in our preliminary analysis. Assuming the height of faint meteors at 100 km, the derived flux of sporadic meteors is about 5x10^{-4} km^{-2}s^{-1}. Although the analysis is still on going, it is clear that this CMOS sensor is useful and effective for observing faint meteors.

  24. Faint-meteor survey with a large-format CMOS sensor
    Date
    July 2014
    Article
    Asteroids, Comets, Meteors 2014. Proceedings of the conference held 30 June - 4 July, 2014 in Helsinki, Finland. Edited by K. Muinonen et al.
    Authors
    Watanabe, J.; Enomoto, T.; Terai, T.; Kasuga, T.; Miyazaki, S.; Oota, K.; Muraoka, F.; Onishi, T.; Yamasaki, T.; Mito, H.; Aoki, T.; Soyano, T.; Tarusawa, K.; Matsunaga, N.; Sako, S.; Kobayashi, N.; Doi, M.
    Abstract

    For observing faint meteors, we need a large telescope or similar optics, which always give a restriction of the field of view. It is a kind of trade-off between the high sensitivity by using larger telescope and narrower field of view. Reconciling this contradiction, we need a large-format imaging detector together with fast readout for meteor observations. A high-sensitivity CMOS sensor of the large format was developed by Canon Inc. in 2010[1]. Its size is 202 mm×205 mm which makes it the largest one-chip CMOS sensor in the world, and approximately 40 times the size of Canon's largest commercial CMOS sensor as shown in the figure. The number of pixel is 1280×1248. Because the increased size of the new CMOS sensor allows more light to be gathered, it enables shooting in low-light environments. The sensor makes image capture possible in one-hundredth the amount of light required by a 35 mm full-frame CMOS sensor, facilitating the shooting of 60 frame-per-second video with a mere 0.3 lux of illumination. We tried to use this large-format CMOS sensor attached to the prime focus of the 1.05-m (F3.1) Schmidt telescope at the Kiso Observatory, University of Tokyo, for surveying faint meteors. The field of view is 3.3 by 3.3 degrees. Test observations including operation check of the system were carried out in January 2011, September 2011,and December 2012. Images were obtained at a time resolution of 60 frames per second. In this system, the limiting magnitude is estimated to be about 11-12. Because of the limitation of the data storage, full-power observations (14-bit data per 1/60 second) were performed for about one or two hours each night. During the first period, we can count a sporadic meteor every 5 seconds. This is about one order higher detection rate of the faint meteors compared with the previous work[2]. Assuming the height of faint meteors at 100 km, the derived flux of the sporadic meteors is about 5 × 10^{-4} km^{-2} sec^{-1}. The last run was performed during the active period of the Geminid meteor shower. We could take valuable data on December 12 and 13. The result will be given in this presentation, together with the future potential of the large format CMOS sensor.

  25. Comet C/2012 S1 (Ison)
    Date
    December 2013
    Article
    Central Bureau Electronic Telegrams, No. 3767, #1 (2013). Edited by Green, D. W. E.
    Authors
    Sako, S.; Maehara, H.; Motohara, K.; Nishijima, S.; Kikuchi, Y.; Arimatsu, K.; Ohnishi, K.; Sarugaku, Y.; Nakano, S.
    Abstract

    S. Sako, H. Maehara, K. Motohara, S. Nishijima, Y. Kikuchi, and K. Arimatsu, University of Tokyo; K. Ohnishi, Nagano National College of Technology; and Y. Sarugaku, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan, report on their unsuccessful post-perihelion searches for the remnants of comet C/2012 S1, which fell apart near perihelion (cf. CBET 3731, IAUC 9266). Deep CCD searches were made with the Kiso Wide Field Camera (KWFC) + I-band filter on Dec. 7.9 and 16.9 UT, and with a Canon CMOS sensor (unfiltered) on Dec. 12.9 and 13.9, both mounted on the Kiso 1.05-m Schmidt telescope; the field-of-view of the KWFC and the CMOS sensor are 125' x 125' and 22' x 40' (north-south by west-east), respectively. On Dec. 7.9, the area searched spanned 90' x 30'. The table below gives the imaging time, the center of the field-of-view, the offset in right ascension and declination (in degrees) of the image center from the predicted ephemeris position (offset computed by S. Nakano, Sumoto, Japan), and the limiting magnitude. 2013 UT R.A. (2000.0) Decl. Delta Delta Limiting R.A. Decl. magnitude Dec. 7.87 16 11 34.4 -00 49 12 0.00- 0.13+ 14.5

Articles

  1. Research of binary neutron star merger phenomenon by high speed sweeping observation
    Date
    November 2020
    Article
    Impact, Volume 2020, Number 5, November 2020, pp. 13-15(3), 10.21820/23987073.2020.5.13
    Authors
    Shigeyama, Toshikazu; Sako, Shigeyuki
    Abstract

    The pursuit of astronomical research has vastly expanded and illuminated our understanding of physics and the laws of the universe. This, in turn, is knowledge useful to a wide range of applications, many that would not have been foreseen in the original research. Astronomy helped create accurate navigation and mapping whilst technologies developed in the pursuit of the stars can be found in many key, everyday devices. Despite millennia of combing the night skies, there are still many mysteries about the universe that we do not yet understand. Professor Toshikazu Shigeyama and Associate Professor Shigeyuki Sako based at the Research Center for the Early Universe (RESCEU) and Institute of Astronomy (IoA), The University of Tokyo, Japan, are two astronomers working to uncover new information about our universe. They have led a team of researchers who were responsible for creating a new astronomical camera, the Tomo-e Gozen. This device will be capable of helping to shed light on several unknowns through the use of sensors able to capture images much closer together in time than ever before.