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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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STRUCTURAL AND DYNAMICAL PROPERTIES OF 29 GALACTIC GLOBULAR CLUSTERS
Sohn, Young-Jong ; Chun, Mun-Suk ; Yim, Hong-Suh ; Byun, Yong-Ik ;
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 179~193
We use B band CCD images to investigate the surface brightness distributions and dynamical properties of 29 Galactic globular clusters. Model fits suggest that 22 clusters show King type surface brightness profiles, while 7 clusters are characterized by power law cusp profiles. For the King type clusters, concentration parameters
range from 1.20 to 2.10, and core radii are 0.4 to 1.9 pc. The mean value of power law slopes of 7 cuspy clusters was estimated as
. Total masses of King type globular clusters are in the range of
with a mean of
. A significant positive correlation between mass and mass-to-light ratio of King type globular clusters has been confirmed with a Pearson's correlation coefficient r = 0.52 and a confidence level of 99%. Our data also confirm a linear relation between total mass and absolute magnitude of King type globular clusters.
NEAR-INFRARED PHOTOMETRY OF METAL RICH GLOBULAR CLUSTER M71
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 194~201
We have carried out JK near-infrared photometry for the central region of the metal rich globular cluster M71, whose (K, J - K) color-magnitude diagram is presented here. Using two independent methods we derive the distance modulus to M71, 12.89 and 12.86
respectively. The former is derived using the HB luminosity
(HB) = -1.15 for globular clusters having metallicity between -1.0 to -0.3 (Kuchinski et al. 1995). The latter is derived through a comparison with IR photometry of stars in the similar metallicity cluster 47 Tuc. We also estimate the reddening to M71, E(J - K) = 0.13, based on E(B - V) = 0.04 of 47 Tuc.
MODEL INFRARED SPECTRA FOR PROTO STARS
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 202~206
We have modeled the infrared spectral energy distributions of proto stars with close attention to the dust envelopes around the stars. The observed spectral energy distributions are closely compared with our models. The model results and observations are compared on IRAS color-color diagrams. Typical model results can explain the observations fairly well.
CLASSIFICATION OF OGLE VARIABLES IN GALACTIC BULGE
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 207~215
The miscellaneous variables observed by OGLE Project of searching for dark matter in our Galaxy have been analyzed to find their characteristics. We investigated evolutionary status, shape of light curve, relationship between orbital period and amplitude of light variation for the miscellaneous variables. The miscellaneous variables except ellipsoidal variables are subgiants or giants. The shapes of the light curves are similar to those of nearby RS CVn type stars. The amplitudes of the light variations decrease rapidly as increasing their orbital periods for the variables whose periods are shorter than 30 days, while the amplitudes decrease slowly for the variables whose periods are longer that 30 days. Thus the OGLE miscellaneous variables are classified as the RS CVn type stars.
SS Lac IN OPEN CLUSTER NGC 7209
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 216~224
We present IUE observations in far ultraviolet region for SS Lac in open cluster NGC 7209. The IUE short wavelength spectrum and long wavelength spectrum were merged to produce an energy distribution curve between
. The curve has been unreddened to take out reddening effect. Then the surface temperature, gravity and abundance of SS Lac were determined based on the Kurucz model atmosphere. The photographic light curve produced before cessation of eclipse were analyzed for photometric solutions. We confirmed SS Lac is a member of open cluster NGC 7209 based on its possible distance. The main reason for the cessation of eclipse is the change of the system's orbital inclination rather than collisional merge of two stars.
LIGHT CURVE SOLUTION OF THE CONTACT BINARY AW UMa
Jeong, J.H. ; Lee, Y.S. ; Yim, J.R. ;
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 225~232
A total of 1088 observations (272 in B, 272 in V, 272 in R, and 272 in I) were made from January to February in 1995 at Chungbuk National University observatory(CbNUO). We constructed BVRI light curves with our data. The photometric solution of these light curves was obtained by means of the Wilson-Devinney method. Our result was compared with those by previous investigators.
A PHOTOMETRIC STUDY FOR A CLOSE BINARY RZ Cas
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 233~241
New UBV Photometric observations for a close binary RZ Cas were obtained at the Chungbuk National University Observatory for 42 nights from October 1991 to March 1993, and standardized UBV light curves were constructed. From the primary light curves, the eight minimum times were determined by using a new light element. We confirmed the primary minimum was totality and derived the average duration was 18.1 minutes corresponding to
. The photometric and spectroscopic solutions were calculated with the obtained light curves and the radial velocity curves of Duerbeck & Hanel(1979) by using Wilson-Devinney method. From these values, the absolute dimensions of this binary system were estimated.
PERIOD CHANGE OF W UMa TYPE CONTACT BINARY AB And
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 242~250
The CCD photometric observations of W UMa-type eclipsing binary AB And were made from September 1994 to October 1996. New four primary minimum times were obtained from these observations. The analysis of times of minimum light for AB And confirms other previous studies that the orbital period of AB And have been changing as a form of sinusoidal variation. In this paper, we calculated the new orbital elements with linear and nonlinear quadratic term, and the best fit equation is derived with the assumption that the period variation of AB And changes sinusoidal pattern. From the sinusoidal term of this orbital element, we calculate period variation as 92 years with amplitude of
. However this result considering only sinusoidal term, was not satisfied with our recent observations. Thus, by assuming another parabolic period variation with the sinusoidal pattern, we derived the best fit orbital elements. From the quadratic coefficient of this orbital elements, we calculated the secular variation of 0.73 seconds, and from the sinusoidal term, the period variation turned out to be 62.9 years with amplitude of
. If we assume only the sinusoidal period variation of AB And, the period has to be decreased within 10 years. However if we consider quadratic term with the sinusoidal period variation of the light elements, the period is expected to be increased. Therefore long-term observations of this binary system are required to confirm this issue.
-Ne DIMERS IN JOVIAN ATMOSPHERES
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 251~258
The detection of jovian hydrogen-hydrogen dimers through the clear telluric 2-micron window(Kim et al. 1995, Trafton et al. 1997( suggests possibility to detect noble gases in the form of dimer with hydrogen in jovian atmospheres. Since noble noble gases do not have spectral structures in the infrared, it has been difficult to derive their abundances in the atmospheres of jovian planets. If there is a significant component of noble gases other than helium in the jovian atmospheres. it might be detected through its dimer spectrum with hydrogen molecule. The relatively sharp spectral structures of hydrogen-argon and hydrogen-neon dimers compared with those of hydrogen-hydrogen dimers are useful for the detection, if an adequate signal-to-noise (S/N) is obtained. If we use a large telescope, such as the Keck telescope, with a long exposure time (>24 hours), then
spectral structure may be detected.
PROTOTYPE DEVELOPMENT OF CCD IMAGING SYSTEM FOR ASTRONOMICAL APPLICATIONS
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 259~268
We present the development process of a prototype CCD imaging system which is being built at Korea Astronomy Observatory(KAO) for astronomical applications. The CCD imaging system requires very low noise and high stability characteristics and is widely used for astronomical purposes from infrared to ultraviolet wavelength regions. However its system design, particularly for the controller design technique, as heart of the system, is not secured in Korea so far. The prototype electronics developed in this study consists of a signal chip controller which was implemented in an EPLD(Erasable Programable Logic Device) and an analog driver, a video processor with a LN2 cooling cryostat. A PC system was employed to control the whole system and to store the image data considering compatibility of the system. We have successfully obtained the first image in the laboratory with the prototype of this imaging system, and an image of the M15 at Sobaeksan Astronomy Observatory.
TEMPERATURE DISTRIBUTION OF THE IONOSPHERIC PLASMA AT FLAYER
Rhee, Hwang-Jae ;
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 269~274
Langmuir probe was housed in the sounding rocket to test the probe's performance and to find the environmental parameters at the F layer of the ionosphere. The gold plated cylindrical probe had a length of 14㎝ and a diameter of 0.096 ㎝. The applied voltage to the probe consisted of 0.9 sec fixed positive bias followed by 0.1 sec of down/up sweep. This ensured that the probe swept through the probe's current-voltage characteristic at least once during 1 second quiescent periods enabling the electron temperature to be measured during the undisturbed times of the flight. The experimental results showed good agreement of the temperature distribution with IRI model at the lower F layer. In the upper layer, the experimental temperatures were 100-200K lower than the IRI model's because of the different geomagnetic conditions: averaged conditions were used in IRI model and specific conditions were reflected in the experiment.
SIMULTANEOUS OBSERVATIONS OF PI 2 PULSATIONS ON THE SATELLITE AND GROUND-BASED MEASUREMENTS
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 275~285
We have investigated Pi 2 pulsations which were observed both on ground magnetometer array and by satellites. On November 9th in 1994, Pi 2 pulsations appeared globally on the 190/210 magnetometer chain and Hermanus station when two satellites(EXOS-D and ETS-VI) were located near the magnetic meridian of the 210 array. The local time of measurements covers from morning(LT=8.47hr) to afternoon(LT=20.3hr) and the bandwidth of peak frequency is found relatively small. The signals of the electric field are highly coherent with ground-based observations with the out of phase oscillations. However, the magnetic field measurement on the ETS-VI in the outer magnetosphere(L=6.60) shows no signature of Pi 2 pulsations over the same time interval and the correlation with any of the ground-based stations is found to be very weak, even through both satellites and magnetometer chain are located close to each other in local time. We suggest that this event may be a direct evidence of Pi 2 pulsations as virtual resonant modes which are localized in the plasmasphere(Lee 1996). The results show that the cavity mode oscillations can occur in the inner magnetosphere with less spectral noise compared to the outer magnetospheric case.
CASE STUDIES ON MHD WAVE PROPAGATION BY THE EXOS-D ELECTRIC FIELD MEASUREMENTS
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 286~296
Magnetohydrodynamic wave phenomena have been investigated in the deep plasmasphere by the electric field measurements in the EXOS-D(Akebono) satellite. EXOS-D has highly eccentric orbits(the perigee: 274km, the apogee: 10,500km), which allows relatively long observational time interval near the apogee region compared to other satellites which pass by the same region with less eccentric orbits. Case studies are performed on one month data of October in 1989 where the apogee is located near the equator and the magnetic local time is about 9:00-12:00 a.m. in the dayside plasmasphere. The observational region ranges from L=2 to L=3 and the magnetic latitude is restricted to less than 30 degrees. The power spectrum is examined for each 128 point series of 8-sec averaged data through a FFT, which covers f = 0~62.3 mHz frequency bands. The results are well consistent with field line resonances (FLRs) and cavity modes in the plasmasphere.
TEMPERATURE AND PRESSURE DEPENDENCES ON THE ISOTOPIC FRACTIONATION EFFECT IN THE THERMAL DECOMPOSITION OF OZONE
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 297~311
To understand the mass-independent isotopic fractionation effects, thermal decomposition of ozone was performed. Initial oxygen gas was converted to ozone completely. Then, the ozone was decomposed to oxygen at various temperatures (
). Isotopic compositions of product oxygen and residual ozone were measured using a stable isotope mass spectrometer. The experimental results were compared with the studies which were performed at the similar conditions. From the raw experimental data, the functions of the instantaneous fractionation factors were calculated by the least square fit. The results clearly showed the temperature dependence. They also showed the pressure dependence and the surface effect. This study may play an important role in the study of ozone decomposition mechanism. It can be applied to explain the mass-independent isotopic pattern found in stratospheric ozone and in meteorites.
DEVELOPMENT OF A FLUXGATE MAGNETOMETER FOR THE KITSAT-3 SATELLITE
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 312~319
The magnetometer is one of the most important payloads for scientific satellite to monitor the near-earth space environment. The electromagnetic variations of the space environment can be observed with the electric and magnetic field measurements. In practice, it is well known that the measurement of magnetic fields needs less technical complexities than that of electric fields in space. Therefore the magnetometer has long been recognized as one of the basic payloads for the scientific satellites. In this paper, we discuss the scientific fluxgate magnetometer which will be on board the KITSAT-3. The main circuit design of the present magnetometer is based on that of KITSAT-1 and -2 but its facilities have been re-designed to improve the resolution to about 5nT for scientific purpose. The calibration and noise level test of this circuit have been performed at the laboratory of the Tierra Tecnica company in Japan.
ICHON SOLAR RADIO SPECTROGRAPHIC SYSTEM AND DEVELOPMENT OF ITS OPERATION SOFTWARE
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 320~329
A solar radio spectrograph for monitoring solar radio emission was installed at Ichon branch of Radio Research Laboratory in 1995. The spectrograph consists of three different antennas to sweep a wide band of frequencies in the range of 30MHz~2500MHz. We have developed the operating software for the acquisition and the analysis of solar radio data obtained by solar radiospectrograph in order to carry out active solar radio observational studies. It was found that by using our software, we could have very good solar radio data for a sequence of three TYPE III bursts observed on 4 Nov. 1997. In this paper, we show the radio spectrograph and the result of the observation by its operating software.
A STUDY FOR THE DETERMINATION OF KOMPSAT I CROSSING TIME OVER KOREA (I): EXAMINATION OF SOLAR AND ATMOSPHERIC VARIABLES
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 330~346
Korea Multi-Purpose Satellite I (KOMPSAT-I, the first multi-purpose Korean satellite) will be launched in the third quarter of 1999, which is operated on the sun-synchronous orbit for cartography, ocean color monitoring, and space environment monitoring. The main mission of Electro-Optical Camera(EOC) which is one of KOMPSAT-I sensors is to provide images for the production of scale maps of Korea. EOC collects panchromatic imagery with the ground sample distance of 6.6m at nadir through visible spectral band of 510~730nm. For determining KOMPSAT-I crossing time over Korea, this study examines the diurnal variation of solar and atmospheric variables that can exert a great influence on the EOC imagery. The results are as follows: 1) After 10:30 a.m. at the winter solstice, solar zenith angle is less than
and expected flux of EOC spectral band over land for clear sky is greater than about
. 2) For daytime the distribution of cloud cover (clear sky) shows minimum (maximum) at about 11:00 a.m. Although the occurrence frequency of poor visibility by fog decreases from early morning toward noon, its effect on the distribution of clear sky is negligible. From the above examination it is concluded that determining KOMPSAT-I crossing time over Korea between 10:30 and 11:30 a.m. is adequate.
DEVELOPMENT OF A S/W SYSTEM FOR RELATIVE POSITIONING USING GPS CARRIER PHASE
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 347~354
We developed a GPS phase data processing S/W system which calculates baseline vectors and distances between two points located in the surface of the Earth. For this development a Double-Difference mothod and L1 carrier phase data from GPS(Global positioning System) were used. This S/W system consists of four main parts: satellite position calculation, Single-Difference equation, Double-Difference equation, and correlation. To verify our S/W, we fixed KAO(
), one of the International GPS Services for Geodynamics, which is located at Tae-Jon, and we measured baseline vectors and relative distances with data from observations at approximate baseline distances of 2.7, 42.1, 81.1, 146.6km. Then we compared the vectors and distances with the data which we obtained from the GPSurvey S/W system, with the L1/L2 ION-Free method and broadcast ephemeris. From the comparison of the vectors and distances with the data from the GPSurvey S/W system, we found baseline vectors X, Y, Z and baseline distances matched well within the extent of 50cm and 10cm, respectively.
GROUND TRACK ACQUISITION AND MAINTENANCE MANEUVER MODELING FOR LOW-EARTH ORBIT SATELLITE
Lee, Byoung-Sun ; Eun, Jong-Woo ; Webb, Charles-E. ;
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 355~366
This paper presents a comprehensive analytical approach for determining key maneuver parameters associated with the acquisition and maintenance of the ground track for a low-earth orbit. A livearized model relating changes in the drift rate of the ground track directly to changes in the orbital semi-major axis is also developed. The effect of terrestrial atmospheric drag on the semi-major axis is also explored, being quantified through an analytical expression for the decay rate as a function of density. The non-singular Lagrange planetary equations, further simplified for nearly circular orbits, provide the desired relationships between the corrective in-plane impulsive velocity increments and the corresponding effects on the orbit elements. The resulting solution strategy offers excellent insight into the dynamics affecting the timing, magnitude, and frequency of these maneuvers. Simulations are executed for the ground track acquisition and maintenance maneuver as a pre-flight planning and analysis.
OUTPUT FEEDBACK SLEWING CONTROL OF FLEWIBLE SPACECRAFT BY LYAPUNOV STABILITY THEORY
Kim, Dae-Sik ; Kim, Chun-Hwey ; Bang, Hyo-Choong ;
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 367~374
Slewing maneuver and vibration suppression control of flexible spacecraft model by Lyapunov stability theory are considered. The specific model considered in this paper consists of a rigid hub with an elastic appendage attached to the central hub and tip mass. Attitude control to point and stabilize single axis using reaction wheel type device is tested. To control all flexible modes is so critical to designing an active control law. We therefore considered an direct output feeback control design by using Lyapunov stability theory. It is shown that the ouput feedback control law design with proposed configuration gives satisfactory result in slewing performance and vibration suppression control.
PRECISE ORBIT DETERMINATION OF GPS SATELLITES USING PHASE OBSERVABLES
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 375~380
The accuracy of user position by GPS is heavily dependent upon the accuracy of satellite position which is usually transmitted to GPS users in radio signals. The real-time satellite position information directly obtained from broadcast ephimerides has the accuracy of 3~10 meters which is very unsatisfactory to measure 100km baseline to the accuracy of less than a few mili-meters. There are globally at present seven orbit analysis centers capable of generating precise GPS ephimerides and their orbit quality is of the order of about 10cm. Therefore, precise orbit model and phase processing technique were reviewed and consequently precise GPS ephimerides were produced after processing the phase observables of 28 global GPS stations for 1 day. Initial 6 orbit parameters and 2 solar radiation coefficients were estimated using batch least square algorithm and the final results were compared with the orbit of IGS, the International GPS Service for Goedynamics.
LONG-TERM PREDICTION OF SATELLITE ORBIT USING ANALYTICAL METHOD
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 381~385
A long-term prediction algorithm of geostationary orbit was developed using the analytical method. The perturbation force models include geopotential upto fifth order and degree and luni-solar gravitation, and solar radiation pressure. All of the perturbation effects were analyzed by secular variations, short-period variations, and long-period variations for equinoctial elements such as the semi-major axis, eccentricity vector, inclination vector, and mean longitude of the satellite. Result of the analytical orbit propagator was compared with that of the cowell orbit propagator for the KOREASAT. The comparison indicated that the analytical solution could predict the semi-major axis with an accuracy of better than
meters over a period of 3 month.
DYNAMIC MODELING AND REACTION WHEEL CONTROLLER DESIGN FOR FLEXIBLE SATELLITE AOCS
Journal of Astronomy and Space Sciences, volume 14, issue 2, 1997, Pages 386~394
In this study, a few of the modeling methods for flexible spacecraft were introduced and adopted to the modeling of a 3-axes stabilization satellite. The generated model was put into pre-built rigid body attitude control loop. A Lumped Parameter Model(Global Mode Model: GMM) was recommended for the absence of the Finite Element Method(FEM) model. Finally, GMM was compared with FEM in terms of designing a control filter. A 1st-order filter was designed to meet requirements of the controller since the new flexible model was applied, and that filter was added to motor controller and axis controller. MATLAB/Simulink was used as a tool for design and simulation of the control loop and filter.