http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
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>
Ishiguro, Masateru,Kuroda, Daisuke,Hanayama, Hidekazu,Takahashi, Jun,Hasegawa, Sunao,Sarugaku, Yuki,Watanabe, Makoto,Imai, Masataka,Goda, Shuhei,Akitaya, Hiroshi,Takagi, Yuhei,Morihana, Kumiko,Honda, IOP Publishing 2015 ASTROPHYSICAL JOURNAL LETTERS - Vol.798 No.2
<P>We report a new observation of the Jupiter family comet 209P/LINEAR during its 2014 return. The comet is recognized as a dust source of a new meteor shower, the May Camelopardalids. 209P/LINEAR was apparently inactive at a heliocentric distance r(h) = 1.6AU and showed weak activity at r(h) <= 1.4AU. We found an active region of <0.001% of the entire nuclear surface during the comet's dormant phase. An edge-on image suggests that particles up to 1 cm in size (with an uncertainty of factor 3-5) were ejected following a differential power-law size distribution with index q = -3.25 +/- 0.10. We derived a mass-loss rate of 2-10 kg s(-1) during the active phase and a total mass of approximate to 5 x 10(7) kg during the 2014 return. The ejection terminal velocity of millimeter- to centimeter-sized particles was 1-4ms(-1), which is comparable to the escape velocity from the nucleus (1.4ms(-1)). These results imply that such large meteoric particles marginally escaped from the highly dormant comet nucleus via the gas drag force only within a few months of the perihelion passage.</P>
OPTICAL AND NEAR-INFRARED POLARIMETRY FOR A HIGHLY DORMANT COMET 209P/LINEAR
Kuroda, Daisuke,Ishiguro, Masateru,Watanabe, Makoto,Akitaya, Hiroshi,Takahashi, Jun,Hasegawa, Sunao,Ui, Takahiro,Kanda, Yuka,Takaki, Katsutoshi,Itoh, Ryosuke,Moritani, Yuki,Imai, Masataka,Goda, Shuhei IOP Publishing 2015 The Astrophysical journal Vol.814 No.2
<P>We conducted an optical and near-infrared polarimetric observation of the highly dormant Jupiter-Family Comet, 209P/LINEAR. Because of its low activity, we were able to determine the linear polarization degrees of the coma dust particles and nucleus independently, that is P-n = 30.3(-0.9)(+1.3)% at alpha = 92 degrees.2 and P-n = 31.0(-0.7)(+1.0)% at alpha = 99 degrees.5 for the nucleus, and P-c = 28.8(-0.4)(+0.4)% at alpha = 92 degrees.2 and 29.6(-0.3)(+0.3)% at alpha = 99 degrees.5 for the coma. We detected no significant variation in P at the phase angle coverage of 92 degrees.2-99 degrees.5, which may imply that the obtained polarization degrees are nearly at maximum in the phase-polarization curves. By fitting with an empirical function, we obtained the maximum values of linear polarization degrees P-max = 30.8% for the nucleus and P-max = 29.6% for the dust coma. The P-max of the dust coma is consistent with those of dust-rich comets. The low geometric albedo of P-v. =. 0.05 was derived from the slope-albedo relationship and was associated with high P-max. We examined P-max-albedo relations between asteroids and 209P, and found that the so-called Umov law seems to be applicable on this cometary surface.</P>