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Urakawa S.,Bisei Spaceguard Center | Okumura S.-I.,Bisei Spaceguard Center | Nishiyama K.,Bisei Spaceguard Center | Sakamoto T.,Bisei Spaceguard Center | And 14 more authors.
Icarus | Year: 2011

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 0.2979day (7.15h) and 0.0993day (2.38h), 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 0.2979day and a precession period of 0.0993day. The shape has a long axis mode (LAM) of L1:L2:L3=1.0:1.0:1.6. The direction of the total rotational angular momentum is around λ=310°, β=-10°, or λ=132°, β=-17°. The nutation angle is approximately constant at 65° (2) 107P/Wilson-Harrington is not a tumbler. The sidereal rotation period is 0.2979day. The shape is nearly spherical but slightly hexagonal with a short axis mode (SAM) of L1:L2:L3=1.5:1.5:1.0. The pole orientation is around λ=330°, β=-27°. 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. © 2011 Elsevier Inc.

Muller T.G.,Max Planck Institute for Extraterrestrial Physics | Durech J.,Charles University | Hasegawa S.,Japan Aerospace Exploration Agency | Abe M.,Japan Aerospace Exploration Agency | And 14 more authors.
Astronomy and Astrophysics | Year: 2010

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 χ2-test reveals a strong preference for a retrograde sense of rotation with a spin-axis orientation of λecl=73°, βecl = -62° and Psid = 7.63 ± 0.01 h. The most likely thermal inertia ranges between 200 and 600 Jm-2s -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). © 2010 ESO.

Hidas M.G.,Las Cumbres Observatory Global Telescope | Hidas M.G.,University of California at Santa Barbara | Hidas M.G.,University of Sydney | Tsapras Y.,Las Cumbres Observatory Global Telescope | And 14 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We have used four telescopes at different longitudes to obtain near-continuous light-curve coverage of the star HD 80606 as it was transited by its ∼4-MJup planet. The observations were performed during the predicted transit windows around 2008 October 25 and 2009 February 14. Our data set is unique in that it simultaneously constrains the duration of the transit and the planet's period. Our Markov Chain Monte Carlo analysis of the light curves, combined with constraints from radial-velocity data, yields system parameters consistent with previously reported values. We find a planet-to-star radius ratio marginally smaller than previously reported, corresponding to a planet radius of Rp = 0.921 ± 0.036RJup. © 2010 The Authors. Journal compilation © 2010 RAS.

Ishiguro M.,Seoul National University | Ham J.-B.,Seoul National University | Tholen D.J.,University of Hawaii at Manoa | Elliott G.T.,University of Hawaii at Manoa | And 13 more authors.
Astrophysical Journal | Year: 2011

We present the optical observations of the Near Earth Object 107P/(4015) Wilson-Harrington during the 2009/2010 apparition taken in search of low-level comet activity. Our photometric and spectroscopic data were collected 28-86 days after the perihelion passage on 2009 October 22 in a wide range of solar phase angles of 39°-68°. A disk-integrated phase function was constructed, giving a geometric albedo of 0.055 ± 0.012, phase integral of q = 0.34, and Bond albedo of AB = 0.019. The photometric property shows a profile similar to low albedo asteroids and comet nuclei. No emission lines were found in our spectrum, giving a flat reflectance similar to low albedo asteroids. Although we could not find any evidence for cometary activity in our photometric and spectroscopic data, we found an upper limit of 0.001% on the fractional active area. We derived the upper limit of the optical depth of the dust trail and tail, 7 × 10-10. We conclude that 107P/(4015) Wilson-Harrington was completely dormant or inactive in the 2009/2010 return. © 2011 The American Astronomical Society. All rights reserved.

Terai T.,Japan National Astronomical Observatory | Urakawa S.,Bisei Spaceguard Center | Takahashi J.,University of Hyogo | Yoshida F.,Japan National Astronomical Observatory | And 6 more authors.
Astronomy and Astrophysics | Year: 2013

Context. The object 2012 DA14 is a near-Earth asteroid with a size of several tens of meters. It had approached closely the Earth on 15 February 2013 UT, providing an opportunity for precise measurements of this tiny asteroid. Aims. The solar phase angle of 2012 DA14 had varied widely around its closest approach but was almost constant during the following night. We performed time-series photometric observations on those two nights to determine the rotational properties and phase effect. Methods. The observations were carried out using the 0.55-m telescope at Saitama University, Japan. The R-band images were obtained continuously over a 2 h period at the closest approach and for about 5 h on the next night. Results. The lightcurve data from the second night indicates a rotational period of 11.0+1.8 -0.6+1.8-0.6 h and a peak-to-peak amplitude of 1.59 ± 0.02 mag. The brightness variation before and after the closest approach was separated into two components that are derived from the rotation and phase effect. We found that the phase curve slope of this asteroid is significantly shallower than those of other L-type asteroids. Conclusions. We suggest that 2012 DA14 is coated with a coarse surface that lacks fine regolith particles and/or a high albedo surface. © 2013 ESO.

Takahashi J.,University of Hyogo | Urakawa S.,Bisei Spaceguard Center | Terai T.,Japan National Astronomical Observatory | Hanayama H.,Japan National Astronomical Observatory | And 6 more authors.
Publications of the Astronomical Society of Japan | Year: 2014

We present the results of our JHKs photometry of asteroid 2012 DA14 at its closest approach to Earth on 2013 February 15. Possible spectral changes associated with resurfacing by planetary encounters are of great interest. The Earth flyby of 2012 DA14 provided a rare opportunity to investigate this effect. Our observations were conducted using the Nishiharima Infrared Camera (NIC) attached to the 2.0 m Nayuta telescope at the Nishi-Harima Astronomical Observatory. Despite the extraordinarily fast sky motion of up to near 50″ s-1, the telescope successfully tracked the asteroid. The NIC achievement of three-band simultaneous observations allowed us to reliably deduce the colors of this fast-moving object. The derived near-infrared relative reflectances are flat, which is consistent with the classification of the asteroid as L-type. The J́-H and H́-Ks colors at 0.5-1 hr after the closest approach are compared with those observed by de León (2013, A&A, 555, L2) at́ ∼ 10 hr after the closest time. We did not detect color changes significantly exceeding the photometric errors, which aré ∼ 0.1 mag. This project has demonstrated the potential of the NIC as a three-band simultaneous imager, especially for observations of rapidly time-variable phenomena. © 2014 The Author.

Itoh R.,Hiroshima University | Fukazawa Y.,Hiroshima University | Tanaka Y.T.,Hiroshima University | Abe Y.,Hokkaido University | And 34 more authors.
Astrophysical Journal Letters | Year: 2013

CTA 102, classified as a flat spectrum radio quasar at z = 1.037, produced an exceptionally bright optical flare in 2012 September. Following the Fermi Large Area Telescope detection of enhanced γ-ray activity, we closely monitored this source in the optical and near-infrared bands for the 10 subsequent nights using 12 telescopes in Japan and South Africa. On MJD 56197 (2012 September 27, four to five days after the peak of bright γ-ray flare), polarized flux showed a transient increase, while total flux and polarization angle (PA) remained almost constant during the "orphan polarized-flux flare." We also detected an intra-night and prominent flare on MJD 56202. The total and polarized fluxes showed quite similar temporal variations, but the PA again remained constant during the flare. Interestingly, the PAs during the two flares were significantly different from the jet direction. The emergence of a new emission component with a high polarization degree (PD) up to 40% would be responsible for the observed two flares, and such a high PD indicates the presence of a highly ordered magnetic field at the emission site. We argue that the well-ordered magnetic field and even the observed directions of the PA, which is grossly perpendicular to the jet, are reasonably accounted for by transverse shock(s) propagating down the jet. © 2013. The American Astronomical Society. All rights reserved..

Urakawa S.,Bisei Spaceguard Center | Fujii M.,4500 Kurosaki | Hanayama H.,Japan National Astronomical Observatory | Takahashi J.,University of Hyogo | And 2 more authors.
Publications of the Astronomical Society of Japan | Year: 2013

We present visible spectroscopic observations of a near-earth object (NEO), 2012 DA14. The asteroid 2012 DA14 came close to the Earth's surface on 2013 February 15 at a distance of 27700 km. Its estimated diameter is -45 m. The physical properties of such a small asteroid have not yet been well determined. The close encounter was a good opportunity to conduct a variety of observations. The purpose of this paper is to deduce the taxonomy of 2012 DA14 based on visible spectroscopic observations using the 0.4m F/10 telescope at the Fujii Kurosaki Observatory. We conclude that the taxonomy of 2012 DA14 is L-type in the visible wavelength region. In addition, we refer to the availability of a small, accessible telescope for NEOs smaller than 100 m. © 2013. Astronomical Society of Japan.

Okumura S.-I.,Bisei Spaceguard Center | Okumura S.-I.,Japan National Astronomical Observatory | Yamashita T.,Japan National Astronomical Observatory | Sako S.,Japan National Astronomical Observatory | And 4 more authors.
Publications of the Astronomical Society of Japan | Year: 2011

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 7.8μm=12.4μm 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 I, 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. © 2011. Astronomical Society of Japan.

Urakawa S.,Bisei Spaceguard Center | Abe S.,Nihon University | Ito T.,Japan National Astronomical Observatory | Nakamura T.,Tohoku University
Astronomical Journal | Year: 2014

We present light curve observations and their multiband photometry for near-Earth object (NEO) 2011 XA3. The light curve has shown a periodicity of 0.0304 ± 0.0003 days (= 43.8 ± 0.4 minutes). The fast rotation shows that 2011 XA3 is in a state of tension (i.e., a monolithic asteroid) and cannot be held together by self-gravitation. Moreover, the multiband photometric analysis indicates that the taxonomic class of 2011 XA3 is S-complex, or V-type. Its estimated effective diameter is 225 ± 97 m (S-complex) and 166 ± 63 m (V-type), respectively. Therefore, 2011 XA3 is a candidate for the second-largest, fast-rotating, monolithic asteroid. Moreover, the orbital parameters of 2011 XA3 are apparently similar to those of NEO (3200) Phaethon, but F/B-type. We computed the orbital evolutions of 2011 XA3 and Phaethon. However, the results of the computation and distinct taxonomy indicate that neither of the asteroids is of common origin. © 2014. The American Astronomical Society. All rights reserved.

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