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Polarimetric Observation of (3200) Phaethon, in Preparation for the Upcoming DESTINY+ Space Mission
Jooyeon Geem,Masateru Ishiguro,Jun Takahashi,Hiroshi Akitaya,Koji S. Kawabata,Tatsuya Nakaoka,Ryo Imazawa,Fumiki Mori,Daisuke Kuroda,Sunao Hasegawa,Fumi Yoshida,Ko Ishibashi,Tomoko Arai,Tomohiko Sekig 한국천문학회 2022 天文學會報 Vol.47 No.1
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>
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
Optical and Near-infrared Polarimetry of Non-periodic Comet C/2013 US10 (Catalina)
Kwon, Yuna Grace,Ishiguro, Masateru,Kuroda, Daisuke,Hanayama, Hidekazu,Kawabata, Koji S.,Akitaya, Hiroshi,Nakaoka, Tatsuya,Itoh, Ryosuke,Toda, Hiroyuki,Yanagisawa, Kenshi,Lee, Myung Gyoon,Ohta, Kouji American Institute of Physics 2017 The Astronomical journal Vol.154 No.4
<P>We present an optical and near-infrared (hereafter NIR) polarimetric study of a comet C/2013 US10 (Catalina) observed on UT 2015 December 17-18 at phase angles of alpha - 52 degrees.1-53 degrees.1. Additionally, we obtained an optical spectrum and multi-band images to examine the influence of gas emission. We find that the observed optical signals are significantly influenced by gas emission; that is, the gas-to-total intensity ratio varies from 5 to 30% in the RC and 3%-18% in the I-C bands, depending on the position in the coma. We derive the 'gas-free dust polarization degrees' of 13.8% +/- 1.0% in the RC and 12.5% +/- 1.1% in the IC bands and a gray polarimetric color, i.e., -8.7% +/- 9.9% mu m(-1) in optical and 1.6% +/- 0.9% mu m(-1) in NIR. The increments of polarization obtained from the gas correction show that the polarimetric properties of the dust in this low-polarization comet are not different from those in high-polarization comets. In this process, the cometocentric distance dependence of polarization has disappeared. We also find that the RC-band polarization degree of the southeast dust tail, which consists of large dust particles (100 mu m(-1) mm), is similar to that in the outer coma where small and large ones are mixed. Our study confirms that the dichotomy of cometary polarization does not result from the difference of dust properties, but from depolarizing gas contamination. This conclusion can provide a strong support for similarity in origin of comets.</P>
OPTICAL-INFRARED AND HIGH-ENERGY ASTRONOMY COLLABORATION AT HIROSHIMA ASTROPHYSICAL SCIENCE CENTER
UEMURA, MAKOTO,YOSHIDA, MICHITOSHI,KAWABATA, KOJI S.,MIZUNO, TSUNEFUMI,TANAKA, YASUYUKI T.,AKITAYA, HIROSHI,UTSUMI, YOUSUKE,MORITANI, YUKI,ITOH, RYOSUKE,FUKAZAWA, YASUSHI,TAKAHASHI, HIROMITSU,OHNO, MA The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
The Hiroshima Astrophysical Science Center (HASC) was founded in 2004 at Hiroshima University, Japan. The main mission of this institute is the observational study of various transient objects including gamma-ray bursts, supernovae, novae, cataclysmic variables, and active galactic nuclei by means of multi-wavelength observations. HASC consists of three divisions; the optical-infrared astronomy division, high-energy astronomy division, and theoretical astronomy division. HASC is operating the 1.5m optical-infrared telescope Kanata, which is dedicated to follow-up and monitoring observations of transient objects. The high-energy division is the key operation center for the Fermi gamma-ray space telescope. HASC and the high-energy astronomy group in the department of physical science at Hiroshima University are closely collaborating with each other to promote multi-wavelength time-domain astronomy. We report the recent activities of HASC and some science topics pursued by this multi-wavelength collaboration.
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
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>