• Title/Summary/Keyword: properties of comets

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Search for Dormant Comets in the Infrared Asteroidal Catalog

  • Kim, Yoonyoung;Ishiguro, Masateru;Usui, Fumihiko
    • The Bulletin of The Korean Astronomical Society
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    • v.39 no.1
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    • pp.67.2-67.2
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    • 2014
  • Comet nucleus is a solid body consisting of dark dust grains and ice. Cometary volatiles sublimate from subsurface layer by solar heating, leaving behind large dust grains on the surface. Eventually, the appearance could turn into asteroidal rather than cometary. It is, therefore, expected that there would be "dormant comets" in the list of known asteroids. Our research group has undertaken the research on the population of dormant comets. We applied a brand-new asteroidal catalog compiled from data garnered by three infrared astronomical observatories, AKARI, IRAS and WISE. We extracted objects which have comet-like orbits on the basis of their orbital properties (Tisserand parameters with respect to Jupiter, TJ, and aphelion distance, Q). We found that (1) there are a considerable number (>100) of asteroids in comet-like orbits, and (2) 80% of them have low albedo consistent with comets. This result suggest that these low albedo objects could be dormant comets. One unanticipated finding is that 20% of asteroids in comet-like orbit have high albedo similar to S-type asteroids. It is difficult to explain the population of S-type asteroids in comet-like orbits by the classical mechanics theory. We further found that these high-albedo objects are small (D < 2 km) bodies distributed in near-Earth space. We suggest that such high-albedo, small, near-Earth asteroids are susceptible to Yarkovsky effect and injected into comet-like orbits.

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Polarimetry of solar system small bodies using the Seoul National University 61cm telescope and TRIPOL

  • Jin, Sunho;Ishiguro, Masateru;Kwon, Yuna Grace;Geem, Jooyeon;Bach, Yoonsoo P.;Seo, Jinguk;Sasago, Hiroshi;Sato, Shuji
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.1
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    • pp.64.2-64.2
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    • 2019
  • It is known that lights scattered by comets and asteroids are partially polarized. From polarimetric observations of those objects, we can investigate physical properties, such as albedos, sizes of cometary dust particles and regolith of asteroids. Since the polarization degrees of those objects highly depend on their phase angles (Sun-object-observer's angles), long-term monitoring observations are required. Moreover, comets show unforeseeable activations (i.e., outbursts) which need follow-up observations to understand the mechanism. In order to realize such monitoring and transient observations, we installed the Triple-Range Imager and POLarimeter (TRIPOL) on the 61cm telescope of Seoul National University (Hereafter, SNU) Gwanak campus. With this combination, we can obtain g', r', i' bands photopolarimetric images simultaneously with $8.0^{\prime}{\times}8.0^{\prime}$ field of view and pixel resolution of 0.94" pixel-1. Here, we make a presentation regarding the photometric and polarimetric performances of TRIPOL on the SNU 61cm telescope. In addition, we introduce initial polarimetric results of asteroid and comets with the instruments. First, we determine the limiting magnitudes (defined as magnitudes for S/N=5) of $15.17{\pm}0.06$ (g'-band), $15.68{\pm}0.01$ (r'-band), $16.24{\pm}0.03$ (I'-band), respectively, with total 240-seconds exposure (four 60-seconds exposure images, each was taken at different rotation angle for the half-wave plate). Second, we found that the instrumental polarization is negligibly small, ($-0.32{\pm}0.04%$ in the g', $-0.36{\pm}0.05%$ in the r' and $-0.21{\pm}0.04%$ in the i'-bands), while the polarization efficiencies are large enough to maximize the performance (i.e., $97.52{\pm}0.03%$ in the g', $98.83{\pm}0.02%$ in the r' and $99.15{\pm}0.02%$ in the i'-bands). With the instruments, we made observations of three Jupiter-family comets, 21P/Giacobini-Zinner, 38P/Stephan-Oterma, and 46P/Wirtanen and plan to observe one near-Earth asteroid, (433) Eros, on a trial basis. Especially for comets, we discriminate signals from dust and gas to eliminate gas contamination, which are known to change observed degree of linear polarization, using multi-band images. We confirm that the phase angle dependency of these comets are consistent with previous observations, probably because polarimetric property of Jupiter-family comets are broadly homogeneous unlike asteroids. We will also describe future observation plans using TRIPOL and SNU 61cm telescope.

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The polarimetric study of (331471) 1984QY1: an asteroid in comet-like orbit

  • Kim, Jooyeon;Ishiguro, Masateru;Bach, Yoonsoo P.;Kuroda, Daisuke;Naito, Hiroyuki;Kim, Yoonyoung;Kwon, Yuna G.;Imai, Masataka;Kuramoto, Kiyoshi;Watanabe, Makoto
    • The Bulletin of The Korean Astronomical Society
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    • v.42 no.2
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    • pp.50.2-50.2
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    • 2017
  • Spatial distribution of atmosphereless bodies in the solar system provides an important clue as to their origins, namely asteroids from Mainbelt or comets from outer solar system. It is, however, difficult to distinguish asteroids and dormant comets due to their similar appearances. In this study, we conducted a unique observation to differentiate asteroids and dormant comets in terms of 'polarimetry'. We observed (331471) 1984 QY1 (hereafter QY1) at large phase angles using the Multi-Spectral Imager (MSI) on the 1.6-m Pirka Telescope from UT 2016 May 25 to June 24. QY1 is a dormant comet candidate in terms of the dynamical properties (i.e. the Tisserand parameter with respect to Jupiter, TJ = 2.68). We analyzed the polarization degree of QY1 as a function of phase angle and found its maximum polarization degree, $Pmax=8.68{\pm}0.28%$ and $8.72{\pm}0.38%$, in RC-and V-band, respectively, around the phase angle of ${\alpha}=100^{\circ}$. In addition, we obtained the geometric albedo, $pV=0.16{\pm}0.02$ by means of an empirical slope-albedo law. The polarimetric properties and the albedo value we acquired are similar to those of S-type asteroids rather than cometary nuclei. In this presentation, we introduce our observation and findings. In addition, we further discuss a dynamical transportation process from Mainbelt to the current orbit.

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Study of Unidentified Spectral Lines in the High-Resolution Spectra of Comet Machholz (C/2004Q2) (Machholz 혜성(C/2004Q2) 고분산 스펙트럼을 이용한 미확인 분광선 연구)

  • Hwang, Sung-Won;Han, Je-Hee;Sim, Chae-Kyung;Kim, Sang-Joon;Jin, Ho;Im, Myung-Shin;Kim, Kang-Min
    • Journal of Astronomy and Space Sciences
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    • v.26 no.4
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    • pp.487-498
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    • 2009
  • We observed Comet Machholz (C/2004Q2) using the BOES (BOao Echelle Spectograph) at the Bohyunsan Observatory on January 4, 2005. We have studied a wavelength range of $4800{\sim}8100{\AA}$ in order to investigate unidentified spectral lines in the high-resolution spectra of Machholz. We compared the Machholz spectra with the high-resolution spectra of previous comets: Swift-Tuttle, Brorsen-Metcalf, Austin, and 122P/de Vico. We identified many molecular lines, which are previously unknown; and these identifications will be useful information for studying high-resolution spectra of future comets.

Spectropolarimetric Signals of Comet 2P/Encke During Its 2017 Apparition

  • Kwon, Yuna Grace;Ishiguro, Masateru;Kuroda, Daisuke;Kawabata, Koji S.;Nakaoka, Tatsuya;Kawabata, Miho;Uemura, Makoto;Shinnaka, Yoshiharu;Akitaya, Hiroshi;collaboration, OISTER
    • The Bulletin of The Korean Astronomical Society
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    • v.42 no.2
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    • pp.49.1-49.1
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    • 2017
  • Comets are one of the most primordial solar system objects that hold the information of the early days of solar system formation inside their nuclei. Orbiting the Sun, they spew such ancient materials that have been buried for many years, creating dust and gas comae. Cometary dust grains absorb and scatter sunlight radiating the continuous light, while gas molecules form the line emissions. Eachof the comets has its own light patterns, which depends on the physical and chemical properties of the dust and gas components. In this regard, spectropolarimetrycan be a powerful tool to study the properties of cometary constituents free from contamination of each other. This methodology offers a series of information on the polarization degrees of the dust and gas components as well as on wavelength dependence of the polarization degree and polarization angle of cometary dust simultaneously. Herein, we will report the results of the spectropolarimetric study of comet 2P/Encke, which is one of the well-known objects for its shortest orbital period and its prominent aging signals. We performed a spectropolarimetric observation of comet 2P/Encke in its inbound orbit using the Higashi-Hiroshima Optical and Near-Infrared Camera (HONIR) at the Higashi-Hiroshima Observatory, Japan, on UT 2017 February 21 at high phase angle of =75.7 deg. Ourstudy of this interesting comet is the first and only one done through spectropolarimetry in a referred publication. We will discuss the most recent polarimetric results of our study in terms of 2P/Encke' scurrent evolutionary status.

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Multiple Outbursts of a Short-Periodic Comet 15P/Finlay

  • Ishiguro, Masateru;Kuroda, Daisuke;Kim, Yoonyoung;Kwon, Yuna;Hanayama, Hidekazu;Miyaji, Takeshi;Honda, Satoshi;Takahashi, Jun;Watanabe, Jun-Ichi
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.61.2-61.2
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    • 2015
  • 15P/Finlay is one of the Jupiter-Family Comets that has long been known since the late 19 century. The comet maintains the perihelion around 1.0 AU over a century, without showing any prominent activities (i.e. fragmentation or eruption) since the discovery. According to reports in unpublished observations, the comet exhibited an outburst in the middle of 2014 December. We conducted a imaging observation of 15P/Finlay just after the report, from 2014 December 23 to 2015 February 18 using three telescopes (the Okayama Astrophysical Observatory 50-cm telescope, the Ishigakijima Astronomical Observatory 105-cm telescope, and the Nishi-Harima Astronomical Observatory 2-m telescope), which constitute a portion of the OISTER (an inter-university observation network in the optical and infrared wavelengths). As a result of the frequent observations, we witnesses the second outburst around UT 2015 January 16. Such cometary outbursts draw the attention to researchers on ground that they could offer insight into the internal structure of comets, following a historical outburst occurred at 17P/Holmes on 2007 October 23. Although cometary outbursts have been often reported mostly in unpublished observations or unreviewed reports, it should be emphasized that there are not a sufficient number of astrophysical research which characterizes the physical properties by observing the aftermaths. This presentation provides a new observational result of 15P/Finlay outburst. Based on the morphological development of the dust cloud as well as the near-nuclear magnitude, we will derive the kinetic energy of the outburst. Finally we plan to compare the results of 15P/Finlay with those of analogical events at 17P/Holmes and P/2010 V1 (Ikeya-Murakami).

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Global Magnetohydrodynamic Simulation of a Comet : When a Comet Crosses a Heliopheric Sector Boundary

  • Yu, Yi
    • International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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    • v.22 no.1
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    • pp.6-23
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    • 1994
  • A disconnection event (DE) of the cometary plasma tail is one of most spectacular phenomena observed in comets. Yet, for years it has remained one of the great unsolved problems I astronomy and space physics. The solar wind is thought to play a major role in the creation of comet plasma tail (type Ⅰ) disconnection events. The goal of this paper is to present a mechanism that explains the disconnection event in terms of the local conditions at the comet. Comparison of the solar wind conditions and 16 DEs in Halley's comet shows that DEs are associated primarily with crossings of the heliospheric sector boundary and apparently not with any other properties of the solar wind, such as a high speed stream[Yi et al., 1994]. A 3-dimensional resistive magnetohydrodynamic simulation in this paper supports this association by showing that only front-side magnetic reconnection between the reversed interplanetary magnetic fields that exist when a comet crosses the heliospheric sector boundary [Niedner and Brandt, 1978] could reproduce the morphology of a DE, including ray formation [Brandt, 1982].

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SIZE AND ALBEDO PROPERTIES OF MAIN BELT ASTEROIDS BASED ON THE COMPARATIVE STUDY OF INFRARED ASTEROID SURVEYS: IRAS, AKARI, AND WISE

  • Usui, Fumihiko;Hasegawa, Sunao;Ishiguro, Masateru;Muller, Thomas G.;Ootsubo, Takafumi
    • Publications of The Korean Astronomical Society
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    • v.32 no.1
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    • pp.55-57
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    • 2017
  • Presently, the number of known asteroids is more than 710,000. Knowledge of size and albedo is essential in many aspects of asteroid research, such as the chemical composition and mineralogy, the size-frequency distribution of dynamical families, and the relationship between small bodies in the outer solar system or comets. Recently, based on the infrared all-sky survey data obtained by IRAS, AKARI, and WISE, the large asteroid catalogs containing size and albedo data have been constructed. In this paper, we discuss the compositional distribution in the main belt regions based on the compiled data on size, albedo, and separately obtained taxonomic type information.

A Study of Polarimetric Properties of Comet C/2013 US10 (Catalina) in Optical and Near-Infrared Wavelength Regions

  • Kwon, Yuna Grace;Ishiguro, Masateru;Kuroda, Daisuke;Hanayama, Hidekazu;Kawabata, Koji S.;Akitaya, Hiroshi;Itoh, Ryosuke;Nakaoka, Tatsuya;Toda, Hiroshi;Yoshida, Michitoshi;Kawai, Nobuyuki;Watanabe, Jun-Ichi
    • The Bulletin of The Korean Astronomical Society
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    • v.41 no.2
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    • pp.50.2-50.2
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    • 2016
  • Polarization is a rich source of information on the physical properties of astronomical objects. In particular, scattered sunlight by optically thin media (e.g., cometary comae) shows linear polarization of light, which highly depends on the phase angle (an angle between the Sun-Comet-Earth), wavelengths, and physical properties of cometary dust particles such as size, composition, and structures. Here, we present a study of polarimetric properties of non-periodic comet C/2013 US10 (Catalina) in optical and near-infrared wavelength regions obtained from imaging, spectroscopy, and polarimetric observations taken on UT 2015 December 17 - 19 welcoming its (probably) first close approach to the Earth. In this presentation, we want to introduce our progress since the last Korean Astronomical Society meeting (at BEXCO, Busan, 2016 April 14 - 15) especially in terms of spatial variations of degree of linear polarization (DOLP) and its possible scenarios to explain the correlations with other observational results. In particular, we found that there is strong anti-correlation between the gas/dust flux ratio and DOLP at the cometocentric distance of $(2-5){\times}104 km$. Besides, within 10 arcseconds in radii (corresponding to inner coma region of 104 km from the center), the inverse relationship of these two parameters does not hold anymore. We conjecture that the rapid outward increase of DOLP can be supported by either the sublimation/evaporation of icy volatiles, disaggregation of cometary dust particles ejected from the nucleus, and/or difference of dominant dust particle sizes. From our results, we can conclude that comet C/2013 US10 (Catalina) corroborates rather indefinite traditional classification of poalrimetric classes of comets, and provides good opportunity to study less processed material which probably cherishes its memory at the formation epoch of the Solar System.

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Near-infrared polarimetric study of near-Earth object 252P/LINEAR: An implication of scattered light from the evolved dust particles

  • Kwon, Yuna G.;Ishiguro, Masateru;Kwon, Jungmi;Kuroda, Daisuke;Im, Myungshin;Choi, Changsu;Tamura, Motohide;Nagayama, Takahiro;Kawai, Nobuyuki;Watanabe, Jun-Ichi
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.2
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    • pp.44.2-44.2
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    • 2019
  • Comets, one of the least-altered leftovers from the nascent solar system, have probably preserved the primitive structure inside, whereas their surfaces become modified from the initial states after repetitive orbital revolutions around the Sun. Resurfacing makes the surface drier and more consolidated than the bulk nuclei, creating inert refractory dust layer ("dust mantle"). Near-infrared (NIR; 1.25-2.25 m) polarimetry is theoretically expected to maximize contrast of the porosity between inner fresh and evolved dust particles, by harboring more dust constituents in the single wavelength than the optical; thus, intensifies electromagnetic interaction in dust aggregates. Despite such an advantage, only a few studies have been made in this approach mainly due to the limited accessibility of available facilities. Herein, we present our new multi-band NIR polarimetric study of near-Earth object 252P/LINEAR over 12 days near perihelion, together with the results of optical (0.48-0.80m) imaging observations and backward dynamical simulation of the comet. Based on the results, we will characterize the dust properties of the comet and discuss the possible environmental (temperature and UV radiation) effects that could produce the observed phenomena.

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