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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 & Issues
Volume 16, Issue 2 - Dec 1999
Volume 16, Issue 1 - Jun 1999
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ABSORPTION LINE GRADIENTS IN THE SPECTRUM OF AN ELLIPTICAL GALAXY NGC 5864A
Sohn, Young-Jong ; Yoon, Suk-Jin ; Oh, Jung-Min ;
Journal of Astronomy and Space Sciences, volume 16, issue 1, 1999, Pages 1~10
The archival long-slit spectra, covering the wavelength range 4050 ~ 5150
, have been used to investigate the radial behavior of absorption line fea-tures (G4300, Fe4383, Ca4455, Fe4531, and
) of an elliptical galaxy NGC 5846A. The heliocentric recession velocity of NGC 5846 has been derived as
. Fe absorption lines of NGC 5846A show significant radial gradients with the mean slope of $\Delta
/Delta(r")=-0.863\pm0.202$. There is also a significant radial gradient of G band with a slope of
. On the other hand, no radial gradients has been detected on the Ca4455 and
absorptions of NGC 5846A. A metallicity gradient, which is derived from the Fe line gradients, is similar to the abundance gradient predicted by Larson's (1975) dissipative models for the formation of elliptical galaxies. We also note that a galaxy-galaxy interaction could affect the line gradients of NGC 5864A.
LIGHT-TIME EFFECT AND MASS TRANSFER IN THE TRIPLE STAR SW LYNCIS
Journal of Astronomy and Space Sciences, volume 16, issue 1, 1999, Pages 11~20
In this paper all the photoelectric times of minimum for the triple star SW Lyn have been analyzed in terms of light-time effect due to the third-body and secular period decreases induced by mass transfer process. The light-time orbit determined recently by Ogloza et al.(1998) were modified and improved. And it is found that the orbital period of SW Lyn have been decreasing secularly. The third-body revolves around the mass center of triple stars every
in a highly eccentric elliptical orbit(e=0.61). The third-body with a minimum mass of
may be a binary or a white dwarf. The rate of secular period-decrease were obtained as
, implying the mass-transfer from the massive primary star to the secondary. The mass losing rate from the primary were calculated as about
. It is noticed that the mass-transfer in SW Lyn system is opposite in direction to that deduced from it's Roche geometry by previous investigators.
PHOTOMETRIC STUDY OF THE W UMA TYPE ECLIPSING BINARY AK HERCULIS
Journal of Astronomy and Space Sciences, volume 16, issue 1, 1999, Pages 21~30
We perform CCD observations in VRI filters for AK Her during 3 nights in Feb 1997 and Mar 1998 at Mt. Sobaek National Observatory, and obtained 236 images in V, 198 in R, and 197 in I filter. From the data, we construct light curves which contain a pair primary and secondary minima and (O-C) diagram. We analyzed the obtained light curves of AK Her using the Wilson-Devinney code. From the analyses, we find that AK Her is more likely detached or semi-detached than contact system. From the (O-C) diagram, we find that the (O-C) residuals increases out of accordance with the expectation of Borkovits & Hegedus since 1990. However, we cannot identify cause of the periodic variation of the (O-C) residuals.
GENERAL PROPERTIES OF CONTACT BINARY SYSTEM FOR MASS RATIO DISTRIBUTION
Journal of Astronomy and Space Sciences, volume 16, issue 1, 1999, Pages 31~40
With a total 761 contact binary systems in Svechnikov & Kuznetsova(1990)'s catalogue, their physical properties by the mass ratio are investigated - for the early CE type with a common radiative envelope and the late CW type with a common convective envelope. It is found that the early CE type shows a higher temperature difference(
) between the primary and secondary components, and also longer period, than the late CW type. The mass ratio of the CW type are distributed in period, than the late CW type. The mass ratio of the CW type are distributed in smaller ranges, from 0.3 to 0.7, than the CE type. Further, the relation between mass ratio and luminosity for the CW type shows a well-defined linear relation, such as ratio and luminosity for the CW type shows a well-defined linear relation, such as
= 0.01 = 0.89q. In the mass ratio-radii relation, it is confirmed that the physical difference of the CE and CW types is a result of the secondary radius. A new mass ratio-radii relation for the CW type is suggested for both the total radius
and the radius ratio
WAVE MODEL DEVELOPMENT IN MULTI-ION PLASMAS
Journal of Astronomy and Space Sciences, volume 16, issue 1, 1999, Pages 41~52
Near-earth space is composed of plasmas which embed a number of plasma waves. Space plasmas consist of electrons and multi-ion that determine local wave propagation characteristics. In multi-ion plasmas, it is difficult to find out analytic solutions from the dispersion relation in general. In this work, we have developed a model with an arbitrary magnetic field and density as well as multi-ion plasmas. This model allows us to investigate how plasma waves behave when they propagate along realistic magnetic field lines, which are assumed by IGRF(International Geomagnetic Reference Field). The results are found to be useful for the analysis of the in situ observational data in space. For instance, if waves are assumed to propagate into the polar region, from the equatorial region, our model quantitatively show how polarization is altered along earth travel path.
SUN TRANSIT OUTAGE CONSIDERING SOLOR ACTIVITY AND IT'S APPLICATION TO KOREASAT
Journal of Astronomy and Space Sciences, volume 16, issue 1, 1999, Pages 53~60
The purpose of this paper is to predict Sun Transit Outage phenomenon(Sunout). Sunout had been studied mainly for the case of Geostationary satellite and under the assumption of 'Quiet Sun'. In this paper, we predict sunout phenomenon more precisely for non-geostationary orbit as well as geostationary orbit and specially we considered the degree of solar activity. And we compare the result of the case of C-band and Ku-band. Also the result is applied to the two KoreaSat communication system through calculating the link budget.
ESTIMATION OF PRECIPITABLE WATER VAPOR USING THE GPS
Journal of Astronomy and Space Sciences, volume 16, issue 1, 1999, Pages 61~68
The radio waves transmitted from GPS satellites is delayed by the troposphere as they propagate to Earth-based GPS receivers. The troposphere delay is usually divided into two parts, the dry delay due to the atmospheric gases and the wet delay due to the water vapor. In this study for the month of May in 1998 the GPS data from two stations(Taejon, Suwon) were used to estimate the total troposphere delay in the zenith direction by the least square method. The dry delay in the zenith direction can be evaluated by using surface pressure values at the station, then the zenith wet delay is obtained by removing the zenith dry delay from the total delay. The zenith wet delay is strongly correlated with the total precipitable water. The quality of the estimate has been assessed by comparison with radiosonde data at Osan. We found the food agreement in precipitable water of the GPS estimates and the radiosonde data. The standard deviation of the difference of the difference between the GPS and radiosonde observations was 3.68mm at Suwon.
SATELLITE ATTITUDE SENSING MODEL AND THEIR S/W DEVELOPMENT
Journal of Astronomy and Space Sciences, volume 16, issue 1, 1999, Pages 69~78
We have developed an attitude sensing S/W system, one of modules of Mission Analysis System(MAS), which simulates attitude sensing data as almost the same as the real sensor of a satellite in orbit. When attitude elements(
) of a satellite and positions of Earth, Moon, and Sun are given, the S/W system calculates look angles and dihedral angles of each celestial bodies relative to the rotations axis of the satellite. It consists of two sub-modules : One is ephemeris service module which consider the perturbations of four planets(Venus, Mars, Jupiter, Saturn) for positions of Sun and Moon and 4
4 earth gravitational potential terms for a satellite's position. The other is attitude simulation module which generates attitude sensing data. Varying the rotational axis of a satellite and it's orbital elements, we simulated the generating attitude sensing data with this S/W system and discussed their results.
LAUNCH ENVIRONMENTAL TEST FOR KITSAT-3 FM
Journal of Astronomy and Space Sciences, volume 16, issue 1, 1999, Pages 79~88
The satellite experiences the severe launch environment such as vibration, acceleration, shock, and acoustics induced by rocket. Therefore, the satellite should be designed and manufactured to endure such severe launch environments. In this paper, we describe the structure of the KITSAT-3 FM(Flight Model) and the processes and results of the launch environmental test to ensure the reliability during launch period.