Japan Spaceguard Association

Ibara, Japan

Japan Spaceguard Association

Ibara, Japan
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Nimura T.,Japan Spaceguard Association | Ebisuzaki T.,RIKEN | Maruyama S.,Tokyo Institute of Technology
Gondwana Research | Year: 2016

We have identified iridium in an ~5m-thick section of pelagic sediment cored in the deep sea floor at Site 886C, in addition to a distinct spike in iridium at the K-Pg boundary related to the Chicxulub asteroid impact. We distinguish the contribution of the extraterrestrial matter in the sediments from those of the terrestrial matter through a Co-Ir diagram, calling it the "extraterrestrial index" f EX. This new index reveals a broad iridium anomaly around the Chicxulub spike. Any mixtures of materials on the surface of the Earth cannot explain the broad iridium component. On the other hand, we find that an encounter of the solar system with a giant molecular cloud can aptly explain the component, especially if the molecular cloud has a size of ~100pc and the central density of over 2000protons/cm3. Kataoka et al. (2013, 2014) pointed that an encounter with a dark cloud would drive an environmental catastrophe leading to mass extinction. Solid particles from the hypothesized dark cloud would combine with the global environment of Earth, remaining in the stratosphere for at least several months or years. With a sunshield effect estimated to be as large as -9.3Wm-2, the dark cloud would have caused global climate cooling in the last 8Myr of the Cretaceous period, consistent with the variations of stable isotope ratios in oxygen (Barrera and Huber, 1990; Li and Keller, 1998; Barrera and Savin, 1999; Li and Keller, 1999) and strontium (Barrera and Huber, 1990; Ingram, 1995; Sugarman et al., 1995). The resulting growth of the continental ice sheet also resulted in a regression of the sea level. The global cooling, which appears to be associated with a decrease in the diversity of fossils, eventually led to the mass extinction at the K-Pg boundary. © 2016 The Authors.

Okumura S.-I.,Bisei Spaceguard Center | Okumura S.-I.,Japan National Astronomical Observatory | Nishiyama K.,Bisei Spaceguard Center | Urakawa S.,Bisei Spaceguard Center | And 6 more authors.
Publications of the Astronomical Society of Japan | Year: 2012

This paper describes a newly designed wide-band optical filter. It is optimized for deep imaging of small solarsystem bodies. The new filter, which we denote as W i, 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 W i filter.© 2012. Astronomical Society of Japan.

Sakamoto T.,Japan Spaceguard Association | Matsunaga N.,University of Tokyo | Hasegawa T.,Gunma Astronomical Observatory | Nakada Y.,University of Tokyo
Astrophysical Journal Letters | Year: 2012

We report the discovery of two Mira variable stars (Miras) toward the Sextans dwarf spheroidal galaxy (dSph). We performed optical long-term monitoring observations for two red stars in the Sextans dSph. The light curves of both stars in the I c band show large-amplitude (3.7 and 0.9 mag) and long-period (326 ± 15 and 122 ± 5 days) variations, suggesting that they are Miras. We combine our own infrared data with previously published data to estimate the mean infrared magnitudes. The distances obtained from the period-luminosity relation of the Miras (75.3+12.8 -10.9 and 79.8+11.5 - 9.9 kpc, respectively), together with the radial velocities available, support memberships of the Sextans dSph (90.0 ± 10.0 kpc). These are the first Miras found in a stellar system with a metallicity as low as [Fe/H] ∼ -1.9 than any other known system with Miras. © 2012. The American Astronomical Society. All rights reserved.

Thuillot W.,Lille University of Science and Technology | Bancelin D.,Lille University of Science and Technology | Bancelin D.,University of Vienna | Ivantsov A.,Lille University of Science and Technology | And 75 more authors.
Astronomy and Astrophysics | Year: 2015

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. © 2015 ESO.

Okumura S.-I.,Bisei Spaceguard Center | Okumura S.-I.,Japan National Astronomical Observatory | Yanagisawa T.,Japan Aerospace Exploration Agency | Nakaya H.,Japan National Astronomical Observatory | And 5 more authors.
Publications of the Astronomical Society of Japan | Year: 2013

"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. © 2014 The Author 2014. Published by Oxford University Press on behalf of the Astronomical Society of Japan. All rights reserved.

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