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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of Astronomy and Space Sciences
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The Korean Space Science Society
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Volume 14, Issue 2 - Dec 1997
Volume 14, Issue 1 - Jun 1997
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COLOR GRADIENTS WITHIN GLOBULAR CLUSTERS: RESTRICED NUMERICAL SIMULATION
Sohn, Young-Jong ; Chun, Mun-Suk ;
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 1~17
The results of a restricted numerical simulation for the color gradients within globular clusters have been presented. The standard luminosity function of M3 and Salperter's initial mass functions were used to generate model clusters as a fundamental population. Color gradients with the sample clusters for both King and power law cusp models of surface brightness distributions are discussed in the case of using the standard luminosity function. The dependence of color gradients on several parameters for the simulations with Salpter's initial mass functions, such as slope of initial mass functions, cluster ages, metallicities, concentration parameters of King model, and slopes of power law, are also discussed. No significant radial color gradients are shown to the sample clusters which are regenerated by a random number generation technique with various parameters in both of King and power law cusp models of surface brightness distributions. Dynamical mass segregation and stellar evolution of horizontal branch stars and blue stragglers should be included for the general case of model simulations to show the observed radial color gradients within globular clusters.
ASCA X-RAY OBSERVATIONS OF TWO CONTACT BINARIES: SW LACERTAE AND W URSAE MAJORIS
Choi, C.S. ; Nam, U.W. ; Kim, Y. ;
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 18~23
We present X-ray light curves and the energy spectra for two contact binaries SW Lac and W UMa, which are obtained from the ASCA(Advanced Satellite for Cosmology and Astrophysics) observations. We find that both sources show appreciable flux variations during the observatoins, and the variations are erratic and are not orbital-phase dependent. From a spectral analysis, we also find that the W UMa spectrum can be reproduced by a variable-abundance plasma model with a single temperature of
, while the SW Lac spectrum requires two different temperatures
EFFECTS OF DENSITY DISTRIBUTION OF THE WIND ON THE LINE PROFILES FOR 32 CYG
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 24~32
We have calculated the velocity distribution of wind driven by Alfven waves. The assumed initial number density of wind can affect the line profiles because it produces the change in the velocity distribution under the mass conservation. Initial density
is chosen for a proper initial density from the observation by Schroder(1986). The wind models for
are calculated at
=0.78. The line profiles for lower initial density show the strong emissions and narrow absorptions because of their steeper velocity gradients.
A PHOTOMETRIC STUDY OF EB-TYPE ECLIPSING BINARY V388 CYG
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 33~43
New BVR CCD photometric observations of EB type close binary V388 Cyg were obtained at the Sobaeksan Astronomy Observatory during 10 nights from October to December 1995. We analyse new 3 color (B, V & R) light curves simultaneously using the Wilson-Devinney code. Now, it is not yet clear whether V388 Cyg is contact or semidetached system. Published epochs of times of minima to data were used to study the changes in period of the system, and calculated a new light elements with the secular terms,
, which indicated the continuous decrease of the period.
PERIOD CHANGES OF W UMa TYPE CONTACT BINARY SS ARIETIS
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 44~58
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
, 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
, 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
. 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
cyclic period with an amplitude of about
to the above periodic change. We also cannot make an acceptable conclusion for it at this time.
THE CHROMOSPHERIC ACTIVITY ON V711 TAU
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 59~66
The relationship between Mg II emission line and light variation of V711 Tau has been derived to investigate the chromospheric activity on V711 Tau. First, a shape of an optical light curve was compared with that of ultraviolet constructed from the IUE low resolution spectra. Second, the intensities of Mg II k emission lines have been reduced from IUE high resolution spectra. The intensity of Mg II k line was compared with brightness of the UV light curve at given phase. The Mg II line intensity is maximum at the phase
where the light is minimum. The evidence of chromosperic activity is indicated by the intensity variation of the MgII emission line with orbital phase for V711 Tau.
THE DESIGN OF QUASI-OPTICS FOR DUAL-CHANNEL SIS RECEIVER
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 67~79
We have designed the quasi optics of the dual channel receiver to observe the radio sources with 100GHz-band and 150GHz-band simultaneously. We introduced the general quasi optics and the relation between the Gaussian beam and thin lens approximation. We determined the parameters of the quasi optic components to match the beam waist at cassegrain focus with that of feed horn well.
RESULTS OF THE TOTAL DOSE EXPERIMENT ON KITSAT-1
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 80~86
High energy particles in the earth's radiation belts cause transient and long term effects on electronic materials, devices, and integrated circuits on board the satellites. Hence, it is very important to have the information on the space radiation environment and the damage on the electronics caused by the se high energy particles. One of the radiation monitor devices frequently used in space is RADFET, a specially designed MOSFET with a thick gate oxide region. The present study focuses on the calibration of RADFET TOT500 using the
source. The result shows that the response of RADFET is very sensitive to the change of temperature. The peculiar behavior observed in the TDE (Total Dose Experiment) on board the KITSAT-1 is identified as the thermal effect due to the change in the eclipse rate of the satellite.
THE EFFECT OF ATMOSPHERIC SCATTERING AS INFERRED FROM THE ROCKET-BORNE UV RADIOMETER MEASUREMENTS
Kim, Jhoon ;
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 87~93
Radiometers in UV and visible wavelengths were onboard the Korean Sounding Rocket(KSR)-1 and 2 which were launched on June 4th and September 1st, 1993. These radiometers were designed to capture the solar radiation during the ascending period of the rocket flight. The purpose of the instrument was to measure the vertical profiles of stratospheric ozone densities. Since the instrument measured the solar radiation from the ground to its apogee, it is possible to investigate the altitude variation of the measured intensity and to estimate the effect of atmospheric scattering by comparing the UV and visible intensity. The visible channel was a reference because the 450-nm wavelength is in the atmospheric window region, where the solar radiation is transmitted through the atmosphere without being absorbed by other atmospheric gases. The use of 450-nm channel intensity as a reference should be limited to the altitude ranges above the certain altitudes, say 20 to 25km where the signals are not perturbed by atmospheric scattering effects.
A STUDY ON TEMPERATURE VARIATION OF THE UPPER THERMOSPHERE IN THE HIGH LATITUDE THROUGH THE ANALYSIS OF 6300
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 94~108
The temperature of the upper thermosphere is generally varied with the solar activity, and largely with geomagnetic activity in the high latitude. The data analyzed in this study are acquired at two ground stations, Thule Air Base(
), Greenland. Both stations are located in the high latitude not only geographically but also geomagnetically. The terrestrial night glow at 6300
from atomic oxygen has been observed from the two ground-based Fabry-Perot interferometers, during periods of 1986~1991 in Thule Air Base and 1986~1994 in
. Some features noted in this study are as follows: (1) The correlation between the solar activity and the measured thermospheric temperature is highest in the case of
in Thule, and increases with the geomagnetic activity in
. (2) The measured temperatures at Thule is generally higher than those at
, but the latter shows steeper slope with the solar activity. (3) The harmonic analysis shows that the diurnal variation(24hrs) is the main feature of the daily temperature variation with a temperature peak at about 13-14 LT (LT=UT-4). However, the semi-diurnal variation is evident during the period of weak solar activity. (4) Generally the predicted temperatures from both MSIS86 and VSH models are lower than the measured temperature, and this discrepancy grows as the solar activity increases. Therefore, we urge modelers to develope a new thermospheric model utilizing broader sets of measurements, especially for high solar activity.
SEASONAL VARIATIONS OF WIND AND TEMPERATURE AT THE MESOPAUSE
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 109~116
The Mesopause (85km) is the boundary between the Mesosphere and the Thermosphere and is very interesting region because there are active fluid dynamic motions and airglow phenomena due to various chemical reactions. But there have been not many studies due to the difficulties of insitu measurement. However in this study we have obtained the Doppler temperatures and winds through the observing Hydroxyl(OH) emission at 843nm using a ground-based Fabry-Perot interferometer. Due to the 2 years of long term observation, we can confirm the seasonal Mesopause temperature variation, which is the opposite trend against the temperature at the ground level, and reveal annual and biannual variations for meridional and zonal wind respectively. These seasonal variations might be the result of the inter-hemispheric circulation.
THE SIMULATION OF A FABRY-PEROT INTERFEROMETER
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 117~125
A Fabry-Perot interferometer has a very high (~1,000,000) resolution, so recently this has been widely used for many fields of space science. To understand the working principle of this a mathematical modeling is needed, and to analyze the interferogram it is essential to know the precise instrument function. The spectrum from the interferometer is mixed with a true signal from the light source and the instrument function through convolution. The true signal has the information about the quantum state of mo lecules, temperature and bulk motion of the gas. Therefore if we model the signal and convolve this with the theoretical instrument function we can predict the spectrum for the real case.
INSTALLATION OF THE GEOMAGNETIC FIELD MEASUREMENT NETWORK AND INITIAL MEASUREMENT RESULT
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 126~135
We installed a pair of geomagnetic ground station in Ichon branch of Radio Research Laboratory(Ichon station, N37.1447, E127.5509) and Kyunghee University(Yongin station, N37.1419, E127.0454). We have successfully finished test operation, and we are now setting up a data base for the real time monitoring of the geomagnetic field. We are also going to have another geomagnetic station for the southward direction at Chejuisland(Cheju University) in summer of 1997. By that time, we will have a complete set of geomagnetic data base for the near earth solar-terrestrial environment in real time. In this paper, we compare and analyze the results of geomagnetic field observations from our stations, Kakioka observatory, Wind and Geotail satellites when the coronal mass ejections(CME) occurred on Dec. 2, 1996.
PRECISE ORBIT PROPAGATION OF GEOSTATIONARY SATELLITE USING COWELL'S METHOD
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 136~141
To calculate the position and velocity of the artificial satellite precisely, one has to build a mathematical model concerning the perturbations by understanding and analysing the space environment correctly and then quantifying. Due to these space environment model, the total acceleration of the artificial satellite can be expressed as the 2nd order differential equation and we build an orbit propagation algorithm by integrating twice this equation by using the Cowell's method which gives the position and velocity of the artificial satellite at any given time. Perturbations important for the orbits of geostationary spacecraft are the Earth's gravitational potential, the gravitational influences of the sun and moon, and the solar radiation pressure. For precise orbit propagation in Cowell' method, 40 x 40 spherical harmonic coefficients can be applied and the JPL DE403 ephemeris files were used to generate the range from earth to sun and moon and 8th order Runge-Kutta single step method with variable step-size control is used to integrate the the orbit propagation equations.
STATION-KEEPING MANEUVERS FOR A GEOSTATIONARY SATELLITE USING LINEAR QUADRATIC REGULATOR
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 142~149
This paper applied one of the well-known optimal control theory, namely, linear quadratic regulator(LQR), to the station-keeping maneuvers(SKM) for a geostationary satellite. The boundary conditions to transfer the system with a good accuracy at a terminal time were based upon the predicted orbital data which are created due to the Earth's non-uniform mass distribution's effect during 14 days and due to luni-solar effect during 28 days. Through the linearization of the nonlinear system equation with respect to reference orbit and the numerical integration of Riccati equation, the optimal trajectories and the corresponding control law have been obtained by using LQR. From the comparison of
obtained by LQR with the
obtained anatically by geometric method, Station Keeping Maneuvers(SKM) via LQR may provide comparable results to a real system. Furthermore it will demonstrate the possibility in fuel optimization and life extension of geostationary satellite.
NORTH/SOUTH STATION KEEPING OF GEOSTATIONARY SATELLITE USING MFT
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 150~157
A precise determination of the fuel efficiency is important because North/South station keeping, which controls the inclination of the geostationary orbit, consumes most of the satellie fuel. We estimate the amount of fuel required during the lifetime of the KOREASAT when MFT(Minimum Fuel Target) technique is adopted, and the result is compared to those when MCT(Maximum Compensation Target) and TBCT(Track-Back Chord Target) technique are applied. From this computation, we find that if MFT technique is adopted, the lifetime of the satellite can be extended at least 45 and 15 days, respectively, compared to those consumed with MCT and TBCT technique.
SUN INTERFEREN PREDICTIONS FOR THE KOMPSAT TT&C STATION
Lee, Byoung-Sun ; Lee, Jeong-Sook ;
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 158~165
The Sun interference event predictions for the KOMPSAT TT&C station were performed to analyze the frequency of the event and the impact on the TT&C link. The KOMPSAT orbit was propagated including only J2 geopotential term for maintaining the Sun-synchronism and no other perturbations were included. Local time of ascending node of the KOMPSAT satellite was set to 10h50m00s. The TT&C station was assumed to locate in Taejon and have 9 meter antenna for S-band link. One year of simulation from 1999/07/01 were performed out of 3 year of mission lifetime of KOMPSAT satellite. Total four times of Sun interference events were occurred during 1 year of simulation and those lasted about 50 seconds altogether. The C/N degradation of the TT&C system was calculated about 4dB. The Sun interference event of 50 seconds of year are 0.0076 percents of the S-band contact time when the 30 minute of contact time is assumed in a day.
A STUDY ON SATELLITE DIAGNOSTIC EXPERT SYSTEMS USING CASE-BASED APPROACH
Journal of Astronomy and Space Sciences, volume 14, issue 1, 1997, Pages 166~178
Many research works are on going to monitor and diagnose diverse malfunctions of satellite systems as the complexity and number of satellites increase. Currently, many works on monitoring and diagnosis are carried out by human experts but there are needs to automate much of the routine works of them. Hence, it is necessary to study on using expert systems which can assist human experts routine work by doing automatically, thereby allow human experts devote their expertise more critical and important areas of monitoring and diagnosis. In this paper, we are employing artificial intelligence techniques to model human expert's knowledge and inference the constructed knowledge. Especially, case-based approaches are used to construct a knowledge base to model human expert capabilities which use previous typical exemplars. We have designed and implemented a prototype case-based system for diagnosing satellite malfunctions using cases. Our system remembers typical failure cases and diagnoses a current malfunction by indexing the case base. Diverse methods are used to build a more user friendly interface which allows human experts can build a knowledge base in an easy way.