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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of The Korean Astronomical Society
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The Korean Astronomical Society
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Volume 29, Issue spc1 - Dec 1996
Volume 29, Issue 2 - Oct 1996
Volume 29, Issue 1 - Apr 1996
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CAUSTICS AND GRAVITATIONAL FOCUSING
CHANG KYONG-AE ;
Journal of The Korean Astronomical Society, volume 29, issue 1, 1996, Pages 1~8
When we follow the lines of the trajectory of photons which intersect the circle, the circle may suffer some deformation as approaching to the observer. We consider an infinitesimal light bundle suffering gravitational bending. We examine the deformation of the deflected light bundle due to the gravitational lens. The size of the deformation is expressed in terms of the focal length of the gravitational lens.
EVOLUTION OF SUNSPOTS BASED ON VECTOR MAGNETOGRAM AND
LEE SANG WOO ; YUN HONG SIK ; MOON YONG JAE ; WANG JIA LONG ;
Journal of The Korean Astronomical Society, volume 29, issue 1, 1996, Pages 9~18
We have analyzed vector magnetograms and
filtergrams of two sunspot groups, one in a growing phase and the other in a decaying phase. In this study, the temporal evolution of their magnetic morphology has been investigated in association with solar activity. The morphological variations of the growing and decaying phase of these sunspots revealed in detail the coalescence of small spots into a large spot and the fragmentation of a large spot into many small spots, respectively. Numerous small flares were detected in the spot group during the decaying phase. This seems to be intimately associated with the shearing motions of many spots with different polarities created by fragmentation of a large sunspot. The magnetic flux and the average shear angle are found to be substantially reduced during the decaying phase, especially in the course of the flarings. This implies that the decaying phase of the sunspot is, to some degree, involved with magnetic field cancellation. The growing spot group has not shown any large activities, but numerous small spots have grown into a typical bipolar sunspot.
CLOSE ENCOUNTERS BETWEEN A NEUTRON STAR AND A MAIN-SEQUENCE STAR
LEE HYUNG MOK ; KIM SUNG S. ; KANG HYESUNG ;
Journal of The Korean Astronomical Society, volume 29, issue 1, 1996, Pages 19~30
We have examined consequences of strong tidal encounters between a neutron star and a normal star using SPH as a possible formation mechanism of isolated recycled pulsars in globular clusters. We have made a number of SPH simulations for close encounters between a main-sequence star of mass ranging from 0.2 to 0.7
represented by an n=3/2 poly trope and a neutron star represented by a point mass. The outcomes of the first encounters are found to be dependent only on the dimensionless parameter
, where m and M are the mass of the main-sequence star and the neutron star, respectively,
the minimum separation between two stars, and
the size of the main-sequence star. The material from the (at least partially) disrupted star forms a disk around the neutron star. If all material in the disk is to be acctreted onto the neutron star's surface, the mass of the disk is enough to spin up the neutron star to spin period of 1 ms.
VARIABLE STARS IN THE OPEN CLUSTER M29
KIM SEUNG-LEE ; SEE SEE-WOO ;
Journal of The Korean Astronomical Society, volume 29, issue 1, 1996, Pages 31~41
We present results of time-series CCD photometry for 178 stars in the young open cluster M29 (=NGC6913). Total 1036 V-band CCD frames were collected for five nights between August 12 and September 13, 1994. The photometric precision is about 7.6 mmag for 9th-10th mag stars in M29 with exposure times of 30 seconds. From the dispersion diagram and the light curves, one detached eclipsing binary (HD194378) and two suspected variables are newly discovered.
type variable, V1322 Cyg, which has been known as a member of M29, did not show any light variations during the period of present observations, indicating that it passed the steady phase without the eruption during our observing runs.
VARIABLE STARS IN A FIELD OF THE OLD OPEN CLUSTER M67 PHOTOMETRIC PRECISION OF THE BOAO 1.8M TELESCOPE
KIM SEUNG-LEE ; CHUN MOO-YOUNG ; PARK BYEONG-GON ; LEE SEE-WOO ;
Journal of The Korean Astronomical Society, volume 29, issue 1, 1996, Pages 43~51
We present test results of time-series CCD photometry to investigate the photometric precision of the BOAO (Bohyunsan Optical Astronomy Observatory) 1.8m telescope. A well-known field of the old open cluster M67, which includes two pulsating blue stragglers and two W UMa type binaries, was monitored for 3.5 hours on February 22, 1996. We have collected 148 V frames and 3 B frames. Photometric noises which consist mainly of photon noise and scintillation noise, were lowered down to about 1.9 mmag for stars of
in M67 with exposure time of 20 seconds. From the C-M diagram for M67, a number of observational properties were derived; E(B-V) = 0.03, (V-Mv)o = 9.6, Age = 4 Gyr. We obtained light curves for four known variable stars and confirmed their variational characteristics. The pulsating blue stragglers show a low amplitude (about 0.01 mag) of light variation.
THE MASS OF PROGENITORS OF WHITE DWARFTS IN OPEN CLUSTERS
LEE SEE-WOO ; SUNG HWANKYUNG ;
Journal of The Korean Astronomical Society, volume 29, issue 1, 1996, Pages 53~62
31 white dwarfs in 10 open clusters are examined, and their maximum mass and the upper mass limit of their progenitors are obtained as
respectively, suggesting that the upper mass limit of white dwarfs is less than
The final mass of white dwarfs shows no clear correlation with the initial mass of their progenitors, and it is found that a deficient gap of initial mass exists between
. This gap seems to correspond to the mass range for carbon detonation or deflagration. The total expected numbers of white dwarfs are
in Hyades with 7 known white dwarfs and 17 in Praesepe with 8 known white dwarfs. These known white dwrfs are all younger than the others in both clusters. But one known white dwarf in Pleiades is older one among
expected white dwarfs.
CHEMICAL EVOLUTION OF THE GALAXY: RADIAL PROPERTIES
PARK BYEONG-GON ; KANG YONG HEE ; LEE SEE-WOO ;
Journal of The Korean Astronomical Society, volume 29, issue 1, 1996, Pages 63~73
The previous study of chemical evolution of the Galaxy is extended to the radial properties of the Galactic disk. The present model includes radial dependency of the time-dependent bimodal IMF, radial flow of material in the disk, and the change of type I supernova explosion rate with radial distance from the disk center as model parameters and observed gas and stellar density distributions and metallicity abundance gradient as observational constraints. The results of two models in this study explain the observed gas and stellar density distributions well, with the slope of the gas density gradient in the region of 4.5 kpc
and -0.123dex/kpc in model
, respectively, which fit well the observed gradient of -0.l1dex/kpc. The abundance gradient reproduced in model
is getting flatter with decreasing radius, while that in model
is getting steeper, which fits better the observed abundance gradient. This result shows the necessity of exponentially increasing type I supernova explosion rate with decreasing radius in order to explain the observed abundance gradient in the disk. The fitness of observed density distribution and star formation rate distribution justifies the reliability of time-dependent bimodal IMF as a compound quantitative chemical evolution model of the Galaxy. The temporal variations of metallicity gradients for carbon, nitrogen and oxygen are also shown.
DISTRIBUTION AND CORRELATION WITH EXTINCTION IN L134
MINN YOUNG KEY ; LEE HYE KYUNG ;
Journal of The Korean Astronomical Society, volume 29, issue 1, 1996, Pages 75~81
We mapped the
line in the dark nebula L134 using the 14-m Taeduck radio telescope with a 57 arcsec beam and one beam spacing. The cloud has a spherical shape with an intensity peak ridge extended from the northwest to the southeast directions. The halfwidth and the radial velocity of the lines peak at the region of the cloud center. The radial velocity decreases from the cloud center towards the north and south directions. The integrated line intensity distributions in the space-velocity plane show some structure and a velocity gradient. The
clouds and dark clouds are closely related in space in shape, outer boundary, and intensity peak positions. The
integrated line intensity is linearly proportional to the visual extinction.