• Journal of Astronomy and Space Sciences
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• 제41권1호
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• pp.35-42
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• 2024

Sungrazing comets, known for their proximity to the Sun, are traditionally classified into broad groups like Kreutz, Marsden, Kracht, Meyer, and non-group comets. While existing methods successfully categorize these groups, finer distinctions within the Kreutz subgroup remain a challenge. In this study, we introduce an automated classification technique using the densitybased spatial clustering of applications with noise (DBSCAN) algorithm to categorize sungrazing comets. Our method extends traditional classifications by finely categorizing the Kreutz subgroup into four distinct subgroups based on a comprehensive range of orbital parameters, providing critical insights into the origins and dynamics of these comets. Corroborative analyses validate the accuracy and effectiveness of our method, offering a more efficient framework for understanding the categorization of sungrazing comets.

• 천문학회보
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• 제46권2호
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• pp.61.5-62
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• 2021

Interstellar objects (ISOs) provide essential information on the physical and chemical properties of the environment when extrasolar systems are formed. Since 2017, two interstellar objects, 1I/2017 ('Oumuamua) and C/2019 Borisov, have been observed passing our solar system. The first interstellar object, named 1I/2017 ('Oumuamua), exhibits several peculiar properties that cannot be explained based on our knowledge of solar system objects, including extreme elongation and non-gravitational acceleration. Its nature and origins remain a mystery. In this talk, I will first describe the basic observational properties of 'Oumuamua and review various theories proposed to explain these features. I will then present our results, ruling out the most promising proposal that 'Oumuamua was made out of molecular hydrogen ice (solid hydrogen). Finally, I will discuss prospects for the detection of ISOs with LSST and in-depth research through multi-wavelength and tracers.

• Journal of Positioning, Navigation, and Timing
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• 제6권2호
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• pp.71-78
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• 2017

The sidereal day of a Global Positioning System (GPS) satellite was intended to equal one half of a sidereal day of the Earth. However, the sidereal day of GPS satellites has become unequal to one half of a sidereal day of the Earth. This is fundamentally caused by the non-sphericity of the Earth and the gravity of the Moon. The difference between sidereal days of GPS satellites and the Earth is known as a sidereal shift. The details surrounding sidereal shifts and their origins have yet to be fully understood. We calculated the periodicity of sidereal shifts for GPS satellites using broadcast ephemeris data. To conduct a periodic analysis of the sidereal shift, we employ the Lomb-Scargle periodogram method. It shows that the orbit periods of GPS satellites have small-amplitude perturbations with a 13.6-day period. In addition, we compare the GPS satellite orbit periods with the periodicity of geomagnetic indices and the solar wind parameters to identify the cause of the perturbations. Our results suggest that the solar wind stream might also affect the 13.6-day period of the sidereal shifts.

• 천문학회보
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• 제44권1호
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• pp.83.1-83.1
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• 2019

Identifying asteroid families, which are groups of asteroids with similar orbital properties, is important for understanding the formation and evolution of the solar system, and probing the origins of Near-Earth Objects (NEOs). Although asteroid taxonomy can be used to identify and refine asteroid families, there are numerous asteroids which are not taxonomically classified yet. Korea Microlensing Telescope Network (KMTNet) can be useful to investigate types of that asteroids, because the telescope can observe a number of asteroids at once by its large field of view. Using KMTNet data, we confirmed that the taxonomic classification of the asteroids is possible by plotting color-color diagram. There is a clear division between C-type and S-type, but ambiguous division between C-type and X-type. In the future, we will observe and classify asteroids which are not classified yet and utilize the data to identify and refine asteroid families.

• 천문학회보
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• 제42권2호
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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.

• 천문학회보
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• 제44권1호
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• pp.65-65
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• 2019

Near-Earth objects consist of a mixture of bodies originated from outer solar system and main asteroidal belt, which are recognized as comets and near-Earth asteroids. In principal, they have orbits distinguishable by their orbital elements. It is, however, that some comets are recognized as asteroids because they could have lost the most of volatile materials in their subsurface layers. Due to their asteroidal appearances, it has been challenging to discriminate such dormant comets from a list of known asteroids. Here we propose to utilize polarimetric technique for finding such dormant comets. We thus conducted a polarimetric observations of three candidates of dormant comet nuclei, (331471) 1984 QY1, (3552) Don Quixote and (944) Hidalgo, by using the 1.6-m Pirka Telescope at the Nayoro observatory (operated by Hokkaido University, Japan). We selected these asteroids in comet-like orbits (ACOs) based on the orbital elements (i.e., the Tisserand parameter with respect to Jupiter TJ < 3). We found that 1984 QY1 has a polarimetric albedo (geometric albedo determined via polarimetry) pV = 0.16 +/- 0.06 while both Don Quixote and Hidalgo have Rc-band polarimetric albedos pR < 0.05. In accordance with the polarimetric result together with a dynamical analysis, we surmised that 1984 QY1 could be an S-type asteroid evolved into the current orbit via 3:1 mean motion resonance with Jupiter. On the contrary, the previous spectroscopic studies indicated that Don Quixote and Hidalgo are classified into D-type taxonomic group, which are typical of comet nuclei. In this presentation, we will introduce our polarimetric observations of ACOs and emphasize that polarimetry is powerful for discriminating the asteroidal and cometary origins.