• Journal of Astronomy and Space Sciences
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• v.19 no.1
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• pp.25-30
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• 2002

Black hole binary candidates are known to be composed of a black hole with 10 $M_{\odot}$ and a K or M type companion. Because the companion is believed to fill the Roche lobe that is very aspherical, the light curves of black hole binaries are characterized by an ellipsoidal variation. It has been known that the ellipsoidal light curves exhibit asymmetric maximum brightness at the orbital phases 0.25 and 0.75, which has been attributed to star spots or the hot impact points of the accretion flow on to the accretion disk around the black hole. In this paper, it is pointed out that the special relativistic beaming effect contributes to the asymmetry of several percent often observed in the light curves. The typical orbital velocity 400 km $s^{-1}$ observed in black hole binaries may induce the temperature difference $\DeltaT/T$ ~ 1/400 of the late type companion star in the observer`s rest frame, because of the special relativistic Doppler beaming effect. This difference in temperature can result in several per cent of brightness sensitively dependent on the wavelength band, which is comparable to what has been observed in most black hole binary candidates. Considering the significant contribution of the special relativistic Doppler beaming effect, we conclude that the estimation of the sizes and temperatures of the star spots or the hot impact point needs serious revision.

• Journal of Astronomy and Space Sciences
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• v.21 no.2
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• pp.153-166
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• 2004

Interplanetary trajectories using the gravity assists are studied for future Korean interplanetary missions. Verifications of the developed softwares and results were performed by comparing data from ESA's Mars Express mission and previous results. Among the Jupiter exploration mission scenarios, multi-planet gravity assist mission to Jupiter (Earth-Mars-Earth-Jupiter Gravity Assist, EMEJGA trajectory) requires minimum launch energy ($C_3$) of 29.231 $Km^2$/$S^2$ with 4.6 years flight times. Others, such as direct mission and single-planet(Mars) gravity assist mission, requires launch energy ($C_3$) of 75.656 $Km^2$/$S^2$ with 2.98 years flight times and 63.590 $Km^2$/$S^2$ with 2.33 years flight times, respectively. These results show that the planetary gravity assists can reduce launch energy, while EMEJGA trajectory requires the longer flight time than the other missions.

• Journal of Astronomy and Space Sciences
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• v.29 no.4
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• pp.381-387
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• 2012

The planetary exploration rover executes various missions after moving to the target point in an unknown environment in the shortest distance. Such missions include the researches for geological and climatic conditions as well as the existence of water or living creatures. If there is any obstacle on the way, it is detected by such sensors as ultrasonic sensor, infrared light sensor, stereo vision, and laser ranger finder. After the obtained data is transferred to the main controller of the rover, decisions can be made to either overcome or avoid the obstacle on the way based on the operating algorithm of the rover. All the planetary exploration rovers which have been developed until now receive the information of the height or width of the obstacle from such sensors before analyzing it in order to find out whether it is possible to overcome the obstacle or not. If it is decided to be better to overcome the obstacle in terms of the operating safety and the electric consumption of the rover, it is generally made to overcome it. Therefore, for the purpose of carrying out the planetary exploration task, it is necessary to design the proper suspension system of the rover which enables it to safely overcome any obstacle on the way on the surface in any unknown environment. This study focuses on the design of the new double 4-bar linkage type of suspension system applied to the Korea Aerospace Research Institute rover (a tentatively name) that is currently in the process of development by our institute in order to develop the planetary exploration rover which absolutely requires the capacity of overcoming any obstacle. Throughout this study, the negative moment which harms the capacity of the rover for overcoming an obstacle was induced through the dynamical modeling process for the rocker-bogie applied to the Mars exploration rover of the US and the improved version of rocker-bogie as well as the suggested double 4-bar linkage type of suspension system. Also, based on the height of the obstacle, a simulation was carried out for the negative moment of the suspension system before the excellence of the suspension system suggested through the comparison of responding characteristics was proved.

• Journal of Astronomy and Space Sciences
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• v.14 no.1
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• pp.44-58
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• 1997

The BVR CCD photometric observations of W UMa-type eclipsing binary SS Ari were made on ten nights from November 1996 to December 1996. Eight new times of minimum lights were derived. The analysis of times of minima of SS Ari confirms the suggestions of other previous investigators that the orbital period of SS Ari have been suffering from a sinusoidal varition. The amplitude and period for the cyclic period changes were calculated as about $58^{y}$ and $0.^{d}053$, respectively. The period variation has been discussed in terms of two potential mechanisms: 1) the light-time effect due to a hypothetical third body and 2) deformations in the convective envelope of a magnetically active component. In the earlier case, the third body has a mass of $1.3M_{\odot}$, if exist, in the form of a white dwarf or a binary system. It seems that the system velocities from the spectroscopic observations supports this interpretation. Meanwhile in the latter case, the primary component is mainly responsible for the magnetic activity of this system with a theoretical amplitude of $\pm0.^{m}08$. However, we cannot make a conclusion which is reasonable explanation at this point, due to lack of observational data. Moreover, the period variation of SS Ari shows duplication about $14^y$, cyclic period with an amplitude of about $0.^d001$ to the above periodic change. We also cannot make an acceptable conclusion for it at this time.

• Journal of the Korean earth science society
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• v.27 no.5
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• pp.557-568
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• 2006

We present CCD UBVI photometry for more than 10,000 stars in $20'.5{\times}20'.5$ field of the halo globular cluster M30. From a color-magnitude diagram, main sequence turnoff was obtained when $V_{TO},\;(B-V)_{TO},\;and\;(V-I)_{TO}\;are\;8.63{\pm}0.05,\;0.44{\pm}0.05\;and\;0.63{\pm}0.05$, respectively. From a (U-B)-(B-V) diagram, reddening parameter, E(B-V) equals $0.05{\pm}0.01$ and a UV color excess ${\delta}(U-B)\;is\;0.27{\pm}0.01$. The abundance is derived, where [Fe/H] equals $-2.05{\pm}0.09$ according to the photometric method and spectroscopic data. The observed luminosity function of M30 shows an excess in the number of red giants relative to the number of turnoff stars, when comparing with the predictions of canonical models. Using the Hipparcos parallaxes for subdwarfs, we estimate distance modulus, $(m-M)_o\;as\;14.75{\pm}0.12$. Using the R and R' method, we find helium abundances, Y(R) as $0.23{\pm}0.02$, Y(R') as $0.29{\pm}0.02$, respectively. Finally, the cluster' sage dispersion was deduced from 10.71 Gyr to 17 Gyr.

• Journal of the Korean Society of Earth Science Education
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• v.14 no.3
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• pp.225-235
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• 2021

The purpose of this study is to obtain implications for the improvement direction of astronomical education methods and development of educational materials or software. In connection with the 5th grade 1st semester elementary science 'Solar System and Stars' unit, elementary pre-service teachers were given a reorganization task to compare the relative distances from the sun to the planets, and then this was analyzed. Pre-service teachers are 11 male and 19 female students in the second year of the music education department at the elementary school teacher training university in B city. The implications of the study results are as follows. First, the 'distance comparison activity using a roll of tissue paper' is suitable for simply comparing the distances from the sun to the planet, but it has limitations in allowing students to experience the vastness of the solar system or inducing student participation-centered classes. Second, it is necessary to develop software materials for elementary school students that can simultaneously reflect the size of the planet and the distance to the planet that can be applied indoors, and also experience the vastness of the solar system, as well as a wide learning space. Third, textbook materials for students have an important influence on the class design of pre-service teachers.

• Journal of Astronomy and Space Sciences
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• v.21 no.1
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• pp.11-28
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• 2004

To better understand how high-latitude electric fields influence thermospheric dynamics, winds in the high-latitude lower thermosphere are studied by using the Thermosphere-ionosphere Electrodynamics General Circulation Model developed by the National Conte. for Atmospheric Research (NCAR-TIEGCM). The model is run for the conditions of 1992-1993 southern summer. The association of the model results with the interplanetary magnetic field(IMF) is also examined to determine the influences of the IMF-dependent ionospheric convection on the winds. The wind patterns show good agreement with the WINDII observations, although the model wind speeds are generally weaker than the observations. It is confirmed that the influences of high-latitude ionospheric convection on summertime thermospheric winds are seen down to 105 km. The difference wind, the difference between the winds for IMF$\neq$O and IMF=0, during negative IMF $B_y$ shows a strong anticyclonic vortex while during positive IMF $B_y$ a strong cyclonic vortex down to 105 km. For positive IMF $B_z$ the difference winds are largely confined to the polar cap, while for negative IMF B, they extend down to subauroral latitudes. The IMF $B_z$ -dependent diurnal wind component is strongly correlated with the corresponding component of ionospheric convection velocity down to 108 km and is largely rotational. The influence of IMF by on the lower thermospheric summertime zonal-mean zonal wind is substantial at high latitudes, with maximum wind speeds being $60\;ms^-1$ at 130 km around $77^{\circ}$ magnetic latitude.

• Journal of Astronomy and Space Sciences
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• v.36 no.1
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• pp.21-33
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• 2019

This paper focuses on the interpretation of radiation fluxes from active galactic nuclei. The advantage of positron annihilation spectroscopy over other methods of spectral diagnostics of active galactic nuclei (therefore AGN) is demonstrated. A relationship between regular and random components in both bolometric and spectral composition of fluxes of quanta and particles generated in AGN is found. We consider their diffuse component separately and also detect radiative feedback after the passage of high-velocity cosmic rays and hard quanta through gas-and-dust aggregates surrounding massive black holes in AGN. The motion of relativistic positrons and electrons in such complex systems produces secondary radiation throughout the whole investigated region of active galactic nuclei in form of cylinder with radius R= 400-1000 pc and height H=200-400 pc, thus causing their visible luminescence across all spectral bands. We obtain radiation and electron energy distribution functions depending on the spatial distribution of the investigated bulk of matter in AGN. Radiation luminescence of the non-central part of AGN is a response to the effects of particles and quanta falling from its center created by atoms, molecules and dust of its diffuse component. The cross-sections for the single-photon annihilation of positrons of different energies with atoms in these active galactic nuclei are determined. For the first time we use the data on the change in chemical composition due to spallation reactions induced by high-energy particles. We establish or define more accurately how the energies of the incident positron, emitted ${\gamma}-quantum$ and recoiling nucleus correlate with the atomic number and weight of the target nucleus. For light elements, we provide detailed tables of all indicated parameters. A new criterion is proposed, based on the use of the ratio of the fluxes of ${\gamma}-quanta$ formed in one- and two-photon annihilation of positrons in a diffuse medium. It is concluded that, as is the case in young supernova remnants, the two-photon annihilation tends to occur in solid-state grains as a result of active loss of kinetic energy of positrons due to ionisation down to thermal energy of free electrons. The single-photon annihilation of positrons manifests itself in the gas component of active galactic nuclei. Such annihilation occurs as interaction between positrons and K-shell electrons; hence, it is suitable for identification of the chemical state of substances comprising the gas component of the investigated media. Specific physical media producing high fluxes of positrons are discussed; it allowed a significant reduction in the number of reaction channels generating positrons. We estimate the brightness distribution in the ${\gamma}-ray$ spectra of the gas-and-dust media through which positron fluxes travel with the energy range similar to that recorded by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) research module. Based on the results of our calculations, we analyse the reasons for such a high power of positrons to penetrate through gas-and-dust aggregates. The energy loss of positrons by ionisation is compared to the production of secondary positrons by high-energy cosmic rays in order to determine the depth of their penetration into gas-and-dust aggregations clustered in active galactic nuclei. The relationship between the energy of ${\gamma}-quanta$ emitted upon the single-photon annihilation and the energy of incident electrons is established. The obtained cross sections for positron interactions with bound electrons of the diffuse component of the non-central, peripheral AGN regions allowed us to obtain new spectroscopic characteristics of the atoms involved in single-photon annihilation.

• Journal of the Korean earth science society
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• v.34 no.4
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• pp.356-367
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• 2013

We study on the concept and reason of seasonal change that 164 university students have. Subsequently the concept types on the seasonal change are classified according to the characteristics and conceptual change after teaching on astronomy. All of the students were simply checked by the questionnaire of multiple choice and essay method before learning on the subjects. And then they answered to questionnaires of similar type after one semester. By the analyzed results, we classify it to three steps of hierarchical concept structure. The first step is the cosmic perspective that is related to the Earth's condition and motion. The second step is the influence of the Earth that is directly affected by the first step. The third step is observer's perspective on the Earth depending on the second step. Among the answers, the first step is prominent and second step is rare. The answers on the reason of seasonal change show some kinds of type which are 1st, 1-2nd, 1-3rd, and 1-2-3rd step. By the result, it is arranged in sequence like as 1-3rd>1st>1-2nd>1-2-3rd type. The lowest number of students was 2nd step of the Sun's altitude and duration of daytime in pre-test. However the students of 2nd step obtained more correct scientific concept on the seasonal change after learning on the subjects, and got the higher score in the post-test than in the pre-test. We found how much important the hierarchical structure on the reason of seasonal change is. As the results, second step on the learning of the Sun's altitude and duration of daytime essentially have to teach after first step. And then third step have to teach. At last, it is sure that the students can obtain the concept of seasonal change.

• Journal of the Korean earth science society
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• v.32 no.4
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• pp.402-410
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• 2011

We present results of CO observations toward an infrared (IR) source, IRAS 07280-1829, and its possibly related molecular clouds. The physical parameters of this IR source such as its infrared slope (${\alpha}$=16) of the Spectral Energy Distribution and bolometric temperature (145 K) indicate that it is an embedded protostar. Its luminosity is ${\sim}2.9{\times}10^4L_{\odot}$, typical of a massive star. The CO profile toward IRAS 07280-1829 has broad wing components, implying a possible existence of CO outflow. The excitation temperature and mass of a molecular cloud (Cloud A) which is thought to harbor the IR source are estimated to be 9~22 K and ~180 $M_{\odot}$, respectively, indicating the Cloud A is a typical infrared-dark cloud. Its LTE mass is found to be much smaller than its virial mass by more than a factor of 10 which is inconsistent with the fact that a protostar recently formed exists in the Cloud A. This may suggest that the environment of the cloud where the IR source is forming is dominant of turbulence and/or magnetic filed, making its virial mass estimated unusually high.