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The opposition effect of the asteroid 4 Vesta
Hasegawa, Sunao,Miyasaka, Seidai,Tokimasa, Noritaka,Sogame, Akito,Ibrahimov, Mansur A.,Yoshida, Fumi,Ozaki, Shinobu,Abe, Masanao,Ishiguro, Masateru,Kuroda, Daisuke Oxford University Press 2014 Publications of the Astronomical Society of Japan Vol.66 No.5
Fumihiko Usui,SUNAO HASEGAWA,Masateru Ishiguro,THOMAS G. MULLER,TAKAFUMI OOTSUBO 한국천문학회 2017 天文學論叢 Vol.32 No.1
Presently, the number of known asteroids is more than 710,000. Knowledge of size andalbedo is essential in many aspects of asteroid research, such as the chemical composition andmineralogy, the size-frequency distribution of dynamical families, and the relationship between smallbodies in the outer solar system or comets. Recently, based on the infrared all-sky survey data obtainedby \emph{IRAS}, \emph{AKARI}, and \emph{WISE}, the large asteroid catalogs containing size and albedo datahave been constructed. In this paper, we discuss the compositional distribution in the mainbelt regions based on the compiled data on size, albedo, and separately obtained taxonomic typeinformation.
Ishiguro, Masateru,Kuroda, Daisuke,Hasegawa, Sunao,Kim, Myung-Jin,Choi, Young-Jun,Moskovitz, Nicholas,Abe, Shinsuke,Pan, Kang-Sian,Takahashi, Jun,Takagi, Yuhei,Arai, Akira,Tokimasa, Noritaka,Hsieh, He IOP Publishing 2014 The Astrophysical journal Vol.792 No.1
<P>We investigated the magnitude-phase relation of (162173) 1999 JU3, a target asteroid for the JAXA Hayabusa 2 sample return mission. We initially employed the International Astronomical Union's H-G formalism but found that it fits less well using a single set of parameters. To improve the inadequate fit, we employed two photometric functions: the Shevchenko and Hapke functions. With the Shevchenko function, we found that the magnitude-phase relation exhibits linear behavior in a wide phase angle range (alpha = 5 degrees-75 degrees) and shows weak nonlinear opposition brightening at alpha < 5 degrees, providing a more reliable absolute magnitude of H-V = 19.25 +/- 0.03. The phase slope (0.039 +/- 0.001 mag deg(-1)) and opposition effect amplitude (parameterized by the ratio of intensity at alpha = 0 degrees.3 to that at alpha = 5 degrees, I(0 degrees.3)/I(5 degrees) = 1.31 +/- 0.05) are consistent with those of typical C-type asteroids. We also attempted to determine the parameters for the Hapke model, which are applicable for constructing the surface reflectance map with the Hayabusa 2 onboard cameras. Although we could not constrain the full set of Hapke parameters, we obtained possible values, w = 0.041, g = -0.38, B-0 = 1.43, and h = 0.050, assuming a surface roughness parameter <(theta)over bar> = 20 degrees. By combining our photometric study with a thermal model of the asteroid, we obtained a geometric albedo of p(v) = 0.047 +/- 0.003, phase integral q = 0.32 +/- 0.03, and Bond albedo A(B) = 0.014 +/- 0.002, which are commensurate with the values for common C-type asteroids.</P>
AKARI/AcuA PHYSICAL STUDIES OF THE CYBELE ASTEROID FAMILY
Kasuga, Toshihiro,Usui, Fumihiko,Hasegawa, Sunao,Kuroda, Daisuke,Ootsubo, Takafumi,Mü,ller, Thomas G.,Ishiguro, Masateru American Institute of Physics 2012 The Astronomical journal Vol.143 No.6
<P>We present a study of 107 Cybele asteroids based on the archival database 'Asteroid Catalog Using AKARI (AcuA)' taken by the Infrared Astronomical Satellite. The database provides diameters D > 10 km, geometric albedos, and taxonomic information (75%) of the Cybeles. We find taxonomic diversity (mainly C-, D-, and P-type) in the population of 78 small Cybeles with diameters 10 km <D < 80 km. Their cumulative power-law size distribution index shows a shallow value of 0.86 ± 0.03. By contrast, 29 large Cybeles with D > 80 km are mostly classified as C- or P-types (90%), with a power-law index of 2.39 ± 0.18. The total mass of Cybele asteroids is estimated to be ~10<SUP>–5</SUP> M<SUB>Earth</SUB>. We also discuss the origin and formation process of the Cybele asteroid family.</P>
OBSERVATIONAL EVIDENCE FOR AN IMPACT ON THE MAIN-BELT ASTEROID (596) SCHEILA
Ishiguro, Masateru,Hanayama, Hidekazu,Hasegawa, Sunao,Sarugaku, Yuki,Watanabe, Jun-ichi,Fujiwara, Hideaki,Terada, Hiroshi,Hsieh, Henry H.,Vaubaillon, Jeremie J.,Kawai, Nobuyuki,Yanagisawa, Kenshi,Kuro IOP Publishing 2011 ASTROPHYSICAL JOURNAL LETTERS - Vol.740 No.1
<P>An unexpected outburst was observed around (596) Scheila in 2010 December. We observed (596) Scheila soon after the impact using ground-based telescopes. We succeeded in the detection of a faint linear tail after 2011 February, which provides a clue to determine the dust ejection date. It is found that the dust particles ranging from 0.1-1 mu m to 100 mu m were ejected into the interplanetary space impulsively on December 3.5 +/- 1.0 day. The ejecta mass was estimated to be (1.5-4.9) x 10(8) kg, suggesting that an equivalent mass of a 500-800 m diameter crater was excavated by the event. We also found that the shape of the light curve changed after the impact event probably because fresh material was excavated around the impact site. We conclude that a decameter-sized asteroid collided with (596) Scheila only eight days before the discovery.</P>
INTERPRETATION OF (596) SCHEILA'S TRIPLE DUST TAILS
Ishiguro, Masateru,Hanayama, Hidekazu,Hasegawa, Sunao,Sarugaku, Yuki,Watanabe, Jun-ichi,Fujiwara, Hideaki,Terada, Hiroshi,Hsieh, Henry H.,Vaubaillon, Jeremie J.,Kawai, Nobuyuki,Yanagisawa, Kenshi,Kuro IOP Publishing 2011 ASTROPHYSICAL JOURNAL LETTERS - Vol.741 No.1
<P>Strange-looking dust cloud around asteroid (596) Scheila was discovered on 2010 December 11.44-11.47. Unlike normal cometary tails, it consisted of three tails and faded within two months. We constructed a model to reproduce the morphology of the dust cloud based on the laboratory measurement of high-velocity impacts and the dust dynamics. As a result, we succeeded in reproducing the peculiar dust cloud by an impact-driven ejecta plume consisting of an impact cone and downrange plume. Assuming an impact angle of 45 degrees, our model suggests that a decameter-sized asteroid collided with (596) Scheila from the direction of (alpha(im), delta(im)) = (60 degrees, -40 degrees) in J2000 coordinates on 2010 December 3. The maximum ejection velocity of the dust particles exceeded 100 m s(-1). Our results suggest that the surface of (596) Scheila consists of materials with low tensile strength.</P>
MULTIBAND OPTICAL OBSERVATION OF THE P/2010 A2 DUST TAIL
Kim, Junhan,Ishiguro, Masateru,Hanayama, Hidekazu,Hasegawa, Sunao,Usui, Fumihiko,Yanagisawa, Kenshi,Sarugaku, Yuki,Watanabe, Jun-ichi,Yoshida, Michitoshi IOP Publishing 2012 ASTROPHYSICAL JOURNAL LETTERS - Vol.746 No.1
<P>An inner main-belt asteroid, P/2010 A2, was discovered on 2010 January 6. Based on its orbital elements, it is considered that the asteroid belongs to the Flora collisional family, where S-type asteroids are common, while showing a comet-like dust tail. Although analysis of images taken by the Hubble Space Telescope and Rosetta spacecraft suggested that the dust tail resulted from a recent head-on collision between asteroids, an alternative idea of ice sublimation was suggested based on the morphological fitting of ground-based images. Here, we report a multiband observation of P/2010 A2 made on 2010 January with a 105 cm telescope at the Ishigakijima Astronomical Observatory. Three broadband filters, g', R-c, and I-c, were employed for the observation. The unique multiband data reveal that the reflectance spectrum of the P/2010 A2 dust tail resembles that of an Sq-type asteroid or that of ordinary chondrites rather than that of an S-type asteroid. Due to the large error of the measurement, the reflectance spectrum also resembles the spectra of C-type asteroids, even though C-type asteroids are uncommon in the Flora family. The reflectances relative to the g' band (470 nm) are 1.096 +/- 0.046 at the R-c band (650 nm) and 1.131 +/- 0.061 at the I-c band (800 nm). We hypothesize that the parent body of P/2010 A2 was originally S-type but was then shattered upon collision into scattering fresh chondritic particles from the interior, thus forming the dust tail.</P>
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>