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Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU<sub>2</sub>
Kuroda, Daisuke,Ishiguro, Masateru,Watanabe, Makoto,Hasegawa, Sunao,Sekiguchi, Tomohiko,Naito, Hiroyuki,Usui, Fumihiko,Imai, Masataka,Sato, Mitsuteru,Kuramoto, Kiyoshi EDP Sciences 2018 Astronomy and astrophysics Vol.611 No.-
<P>We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU2, which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU2 are 44.6 ± 0.5% in the <I>R</I>C band and 44.0 ± 0.6% in the <I>V</I> band at a solar phase angle of 81.0°. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (<0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU2 has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.</P>
Spectral type and geometric albedo of (98943) 2001 CC21, the Hayabusa2# mission target
Jooyeon Geem,Masateru Ishiguro,Mikae,Granvik,Hiroyuki Naito,Hiroshi Akitaya,Tomohiko Sekiguchi,Sunao Hasegawa,Daisuke Kuroda,Tatsuharu Oono,Yoonsoo P. Bach,Sunho Jin,Rio Imazawa,Kaji S. Kawabata,Seiko 한국천문학회 2023 天文學會報 Vol.48 No.2
New evidence supporting past dust ejections from an active asteroid (4015) Wilson-Harrington
Sunho Jin,Jooyeon Geem,Hiroyuki Naito,Jun Takahashi,Hiroshi Akitaya,Daisuke Kuroda,Seitaro Urakawa,Seiko Takagi,Tatsuharu Oono,Tomohiko Sekiguchi,Davide Perna,Simone Ieva,Yoonsoo P. Bach,Hangbin Jo,Ma 한국천문학회 2023 天文學會報 Vol.48 No.2
Polarimetric Study of Near-Earth Asteroid (1566) Icarus
Ishiguro, Masateru,Kuroda, Daisuke,Watanabe, Makoto,Bach, Yoonsoo P.,Kim, Jooyeon,Lee, Mingyeong,Sekiguchi, Tomohiko,Naito, Hiroyuki,Ohtsuka, Katsuhito,Hanayama, Hidekazu,Hasegawa, Sunao,Usui, Fumihik American Institute of Physics 2017 The Astronomical journal Vol.154 No.5
<P>We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles alpha = 57 degrees-141 degrees around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are P-max = 7.32 +/- 0.25% at phase angles of alpha(max) = 124 degrees +/- 8 degrees in the V-band and P-max = 7.04 +/- 0.21% at alpha(max) = 124 degrees +/- 6 degrees in the RC-band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of p(V) = 0.25 +/- 0.02, which is in agreement with that of Q-type taxonomic asteroids. amax is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance q = 0.187 au and a short rotational period of T-rot = 2.27 hr) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon.</P>