• 천문학회보
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• 제42권2호
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• pp.48.3-49
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• 2017

Interplanetary space of the solar system contains a large number of dust particles, referred to as Interplanetary Dust Particles (IDPs) cloud complex. They are observable through meteors and zodiacal lights. The relative contribution of possible sources to the IDPs cloud complex was an controversial topic, however, recent research (Yang & Ishiguro, 2015 and references therein) suggested a dominance of cometary origin. In this study, we numerically investigated the orbital evolution of cometary dust particles, with special concerns on different evolutionary tracks and its consequences according to initial orbits, size and particle shape. The effect of dust particle density and initial size-frequency distribution (SFD) were not decisive in total cloud complex mass and mass supply rate, when these physical quantities are confined by observed zodiacal light brightness and dust particle SFD at 1 au. We noticed that, if we assume the existence of fluffy aggregates discovered in the Earth's stratosphere and the coma of 67P/Churyumov-Gerasimenko, the required mass supply rate decreases significantly. We also found out that close encounters with planets (mostly Jupiter) are the dominating factor of the orbital evolution of dust particles, as the result, the lifetime of cometary dust particles are shorter than Poynting-Robertson lifetime (around 250 thousand years). As another consequence of severe close encounters, only a small fraction of cometary dust particles can be transferred into the orbit < 1 au. This effect is significant for large size particles of ${\beta}$ < 0.01. The exceptional cases are dust particles ejected from 2P/Encke and active asteroids. Because they rarely encounter with Jupiter, most dust particles ejected from those objects are governed by Poynting-Robertson effect and well transferred into the orbits of small semimajor axis. In consideration of the above effects, we directly estimated probability of mutual collisions between dust particles and concluded that mutual collisions in the IDPs cloud complex is mostly ignorable, except for the case of large sized particles from active asteroids.

• 천문학회보
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• 제35권1호
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• pp.48.1-48.1
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• 2010

Four of nine exoplanets found by microlensing were detected by the resonant caustic, which represents the merging of the planetary and central caustics at the position when the projected separation of a host star and a bounded planet is s~1. One of the resonant caustic lensing events, OGLE-2005-BLG-169, was a caustic-crossing high-magnification event with A_max ~800 and the source star was much smaller than the caustic, nevertheless the perturbation was not obviously apparent on the light curve of the event. In this paper, we investigate the perturbation pattern of the resonant caustic to understand why the perturbations induced by the caustic do not leave strong traces on the light curves of high-magnification events despite a small source/caustic size ratio. From this study, we find that the regions with small magnification excess around the center of the resonant caustic are rather widely formed, and the event passing the small-excess region produces a high-magnification event with a weak perturbation that is small relative to the amplification caused by the star and thus does not noticeably appear on the light curve of the event. We also find that the positive excess of the inside edge of the resonant caustic and the negative excess inside the caustic become stronger and wider as q increases, and thus the resonant caustic-crossing high-magnification events with the weak perturbation occur in the range of q $\leq$ 10-4. We determine the probability of the occurrence of events with the small excess $|\varepsilon|{\leq}3%$ in high-magnification events induced by a resonant caustic. As a result, we find that for the Earth-mass planets with a separation of ~2.5 AU the resonant caustic high-magnification events with the weak perturbation can occur with a significant frequen.

• 한국지구과학회지
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• 제30권1호
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• pp.96-110
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• 2009

8학년(중학교 2학년)을 대상으로 '지구와 별' 단원의 지구계 수업 모듈을 개발하였다. 그리고 이 수업 모듈 중 태양계 행성을 학습하는 행성 리모델링 활동을 개발하였다. 이 활동의 핵심은 행성에 생명체가 살 수 있도록 행성을 리모델링하는 것이다. 본 연구에서는 쓰기와 그리기로 표현된 학생들의 생각의 시각화와 이를 통해 학생들의 이해를 해석하였다 학생들의 인지구조를 분석하기 위하여 4개로 법주화된 분석틀을 개발하여 적용하였다. 그리고 인지적 내용 특성을 분석하기 위하여 지구계의 구성 요소별 그리고 과학과 기술의 이용별로 분석 요소를 세분화하여 적용하였다. 행성 리모델링 활동을 통해 분석한 학생들의 인지에는 지구 소양과 같은 지구계 수업의 영향이 나타났다.

• 한국측량학회지
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• 제27권4호
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• pp.437-444
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• 2009

동역학적 방법을 이용한 GPS(Global Positioning System) 위성궤도 결정을 위해 양방향 적분이 가능한 multi-step 방식의 수치적분기를 개발하였으며, 이는 GPS 위성 고도에서 마이크로미터 수준의 정확도를 보였다. 가속도 모델링에서 달, 태양 이외의 천체에 의한 인력은 매우 작으므로 태양복사압에서 경험적 모델로 대체하였다. 위성궤도 미지수는 수치적분된 위성궤도와 IGS(International GNSS Service) 정밀궤도를 이용하여 최소제곱방법으로 결정했다. 이를 위해서는 수치적분기에서 가속도와 함께 미지수에 대한 편미분값을 동시에 적분해야 한다. 추정된 위성궤도 미지수를 이용하여 계산한 잔차의 RMS(Root Mean Squares error)로 부터 위성궤도의 정확도를 검증했다. 2009년 3월 한달의 평균적인 궤도오차 RMS는 5.2mm 였으며, 궤도오차의 절대적인 크기는 위성체의 종류 및 위성진행방향기준 좌표계 상에서 특별히 편향된 형태를 보이지는 않는 것으로 나타났다. 본 연구에서 적용한 태양복사압 모델은 상수항 및 궤도당 1주기에 대한 변화만을 포함하고 있으므로, 궤도당 2주기에 해당하는 궤도오차 양상을 크게 보이고 있으며 이에 대한 추가적인 연구가 필요할 것으로 판단된다.

• 천문학회지
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• 제45권2호
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• pp.39-48
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• 2012

We investigate non-LTE effects on the $H_3^+$ level populations to help the analysis of the observed 2 and 3.5 micron $H_3^+$ emissions from the Jovian ionosphere. We begin by constructing a simple three-level model, in order to compute the intensity ratio of the R(3,4) line in the hot band to the Q(1,0) line in the fundamental band, which have been observed in the Jovian auroral regions. We find that non-LTE effects produce only small changes in the intensity ratios for ambient $H_2$ densities less than or equal to $5{\times}10^{11}cm^{-3}$. We then construct two comprehensive models by including all the collisional and radiative transitions between pairs of more than a thousand known $H_3^+$ rovibrational levels with energies less than 10000 $cm^{-1}$. By employing these models, we find that the intensity ratios of the lines in the hot and fundamental bands are affected greatly by non-LTE effects, but the details depend sensitively on the number of collisional and radiative transitions included in the models. Non-LTE effects on the rovibrational population become evident at about the same ambient $H_2$ densities in the comprehensive models as in the three-level model. However, the models show that rotational temperatures derived from the intensities of rotational lines in the ${\nu}_2$ and $2{\nu}_2$ bands may differ significantly from the ambie temperatures in the non-LTE regime. We find that significant non-LTE effects appear near and above the $H_3^+$ peak, and that the kinetic temperatures in the Jovian thermospheric temperatures derived from the observed line ratios in the 2 and 3.5 micron $H_3^+$ emissions are highly model dependent.

• 천문학논총
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• 제30권2호
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• pp.61-64
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• 2015

The brightness of Io's magnetic footprint, an indicator of electromagnetic interaction at the satellite, appears to be strongly connected to the satellite's distance from the plasma equator. As a result, the brightest footprints were detected when Io is near the interception location between the satellite's orbital plane and the plasma equator. However, volcanic activities on Io show strong correlation with the equatorward shift of Jupiter's main auroral oval, consequently causing the disappearance of Io's footprint. The same conclusion was suggested via the observation of Jupiter's hectometric radio emission, called HOM, which closely corresponds to Jupiter's auroral activity. The plasma environment near the Jovian satellites was found to vary significantly at different observational epochs. The electron density increased by approximately a factor of three from the Voyager epoch (1979) to the Galileo epoch (1995), while the electron density was found to be significantly higher (~ 5 times) in the Cassini epoch (2001). In this current study, the magnetic footprints were clearly brighter ten years ago (from peak brightness in 1998-2001) than the footprints detected in 2007. For volcanic activities on Io in 2007, there are two clear activities in February and late May. The magnetic footprint appeared to be dimmer in March 2007, expected to be the result of volcano activities in Feb 2007. However, the magnetic footprint brightness in June appeared to be slightly brighter than the footprints observed in May. The reason could be the time delay between the brightening of the sodium nebula on approximately May 31st and, a while later, the enhancement of flux tube content peaking on approximately June 5th. On the other hand, Io's magnetic footprints were observed during June 1st - 10th when they may not yet have been affected by the increase in mass outflow due to the increase of plasma density.

• 천문학회보
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• 제36권1호
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• pp.27.2-27.2
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• 2011

The Kepler(NASA) and CoRoT(ESA) space telescopes are surveying thousands of exoplanet for finding Earth-like exoplanets with similar environments of the Earth. Then the TPF(NASA), DARWIN(ESA) and many large-aperture ground telescopes have plan for spectroscopic observations of these earth-like exoplanets in next decades. Now, it has been started to simulate the disk averaged spectra of the earthlike exoplanets for comparing the observed spectra and suggesting solutions of environment of these planets. Previous research, the simulations are based on radiative transfer method, but these are limited by optical models of Earth system and instruments. We introduce a new simulation method, IRT(Integrated Ray Tracing) to overcome limitations of previous method. The 3 components are defined in IRT; 1)Sun model, 2)Earth system model (Atmosphere, Land and Ocean), 3)Instrument model. The ray tracing in IRT is simulated in composed 3D real scale space from inside the sun model to the detector of instrument. The Sun model has hemisphere structure with Lambertian scattering optical model. Atmosphere is composed of 16 distributed structures and each optical model includes BSDF with using 6SV radiative transfer code. Coastline and 5 kinds of vegetation distribution data are used to land model structure, and its non-Lambertian scattering optical model is defined with the semi-empirical "parametric kernel method" used for MODIS(NASA) and POLDER(CNES) missions. The ocean model includes sea ice cap structure with the monthly sea ice area variation, and sea water optical model which is considering non-lambertian sun-glint scattering. Computation of spectral imaging and radiative transfer performance of Earth system model is tested with hypothetical space instrument in IRT model. Then we calculated the disk averaged spectra of the Earth system model in IRT computation model for 8 cases; 4 viewing orientation cases with full illuminated phase, and 4 illuminated phase cases in a viewing orientation. Finally the DAS results are compared with previous researching results of radiative transfer method.

• 한국지구과학회지
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• 제29권3호
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• pp.290-304
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• 2008

이 연구의 목적은 고등학생들의 태양계 상대적인 크기를 쉽게 이해하고 창의적인 사고 능력을 키우기 위한 교육 프로그램 개발이다. 프로그램은 태양계의 상대적 크기 영역에서 4개 주제와 8차시 분량으로 개발되었다. 개발된 프로그램은 구미시에 소재한 G 고등학교 10학년 155명에게 투입하였다. 연구 결과를 살펴보면, 개발된 프로그램 학습을 통해 학생들이 태양계 행성들의 상대적인 크기를 쉽게 이해할 수 있었고, 발산적 사고로부터 수렴적 사고로 이어지는 창의적 사고력을 향상 시켰다. 개발된 프로그램의 주제별 활동을 통하여 학생들에게 창의적 사고 능력의 배양과 태양계내의 행성간 거리와 크기에 대해 쉽게 학습시킬 수 있을 것으로 기대된다.

• 대한기계학회논문집A
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• 제36권9호
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• pp.953-960
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• 2012

풍력발전기용 증속기의 유성기어열에서 한단 지지 캐리어에 유연 핀을 적용하여 유성 축과 유연 핀의 변형에 의한 자기 정렬 효과가 증속기 유성기어열의 수명에 미치는 영향에 대한 연구를 수행하였다. 유성기어열의 하중 분배 효과를 분석하기 위하여 오일러 이론과 상용 프로그램을 이용하였다. 풍력발전기용 증속기에 한단 지지 캐리어와 유연 핀이 사용됨에 따라 유성기어의 미스얼라인먼트, 치면 하중분포 계수 및 요구수명이 만족할 만한 성능 향상을 가져왔으며, 특히 요구수명에 있어서 증속기가 요구하는 20년 보증 수명을 만족하는 것으로 확인되었다.

• 천문학회지
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• 제51권6호
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• pp.197-206
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• 2018

We present the analysis of KMT-2016-BLG-0212, a low flux-variation ($I_{flux-var}{\sim}20mag$) microlensing event, which is in a high-cadence (${\Gamma}=4hr^{-1}$) field of the three-telescope Korea Microlensing Telescope Network (KMTNet) survey. The event shows a short anomaly that is incompletely covered due to the brief visibility intervals that characterize the early microlensing season when the anomaly occurred. We show that the data are consistent with two classes of solutions, characterized respectively by low-mass brown-dwarf (q = 0.037) and sub-Neptune (q < $10^{-4}$) companions. Future high-resolution imaging should easily distinguish between these solutions.