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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.

Takahashi J.,University of Hyogo | Urakawa S.,Bisei Spaceguard Center | Terai T.,Japan National Astronomical Observatory | Hanayama H.,Japan National Astronomical Observatory | And 5 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.

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.

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.

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.

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