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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>
Kwon, Y. G.,Ishiguro, M.,Shinnaka, Y.,Nakaoka, T.,Kuroda, D.,Hanayama, H.,Takahashi, J.,Baar, S.,Saito, T.,Kawabata, M.,Uemura, M.,Morokuma, T.,Murata, K. L.,Takagi, S.,Morihana, K.,Nagayama, T.,Sekig Springer-Verlag 2018 Astronomy and astrophysics Vol.620 No.-
<P><I>Context.</I> Spectropolarimetry is a powerful technique for investigating the physical properties of gas and solid materials in cometary comae without mutual contamination, but only a few spectropolarimetric studies have been conducted to extract each component.</P><P><I>Aims.</I> We attempt to derive the continuum (i.e., scattered light from dust coma) polarization degree of comet 2P/Encke, free of the influence of molecular emissions. The target is unique in that its orbit is dynamically decoupled from Jupiter, like the main-belt asteroids, but it ejects gas and dust like ordinary comets.</P><P><I>Methods.</I> We observed the comet using the Hiroshima Optical and Near-Infrared Camera attached to the Cassegrain focus of the 150 cm Kanata telescope on UT 2017 February 21 when the comet was at the solar phase angle of <I>α</I> = 75°.7.</P><P><I>Results.</I> We find that the continuum polarization degree with respect to the scattering plane is <I>P</I>cont, r = 33.8 ± 2.7% at the effective wavelength of 0.82 <I>μ</I>m, which is significantly higher than those of cometary dust in a high-<I>P</I>max group at similar phase angles. Assuming that an ensemble polarimetric response of the dust of 2P/Encke as a function of phase angle is morphologically similar with those of other comets, its maximum polarization degree is estimated to <I>P</I>max ≳ 40% at <I>α</I>max ≈ 100°. In addition, we obtain the polarization degrees of the C2 swan bands (0.51-0.56 <I>μ</I>m), the NH2<I>α</I> bands (0.62-0.69 <I>μ</I>m), and the CN-red system (0.78-0.94 <I>μ</I>m) in a range of 3-19%, which depend on the molecular species and rotational quantum numbers of each branch. The polarization vector is aligned nearly perpendicularly to the scattering plane with an average of 0°.4 over a wavelength range of 0.50-0.97 <I>μ</I>m.</P><P><I>Conclusions.</I> From the observational evidence, we conjecture that the high polarization degree of 2P/Encke might be attributable to a dominance of large dust particles around the nucleus, which have remained after frequent perihelion passages near the Sun.</P>
Visible-wavelength spectroscopy of subkilometer-sized near-Earth asteroids with a low delta-v
Kuroda, D.,Ishiguro, M.,Takato, N.,Hasegawa, S.,Abe, M.,Tsuda, Y.,Sugita, S.,Usui, F.,Hattori, T.,Iwata, I.,Imanishi, M.,Terada, H.,Choi, Y.-J.,Watanabe, S.-i.,Yoshikawa, M. Astronomical Society of Japan 2014 Publications of the Astronomical Society of Japan Vol.66 No.3