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Journal of The Korean Astronomical Society
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The Korean Astronomical Society
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Volume & Issues
Volume 27, Issue 2 - Oct 1994
Volume 27, Issue 1 - Apr 1994
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STATISTICAL PROPERTIES OF GRAVITATIONAL LENSING IN COSMOLOGICAL MODELS WITH COSMOLOGICAL CONSTANT
LEE HYUN-A ; PARK MYEONG-GU ;
Journal of The Korean Astronomical Society, volume 27, issue 2, 1994, Pages 103~117
To extend the work of Gott, Park, and Lee (1989), statistical properties of gravitational lensing in a wide variety of cosmological models involving non-zero cosmological constant is investigated, using the redshifts of both lens and source and observed angular separation of images for gravitational lens systems. We assume singular isothermal sphere as lensing galaxy in homogenous and isotropic FriedmannLemaitre-Robertson- Walker universe, Schechter luminosity function, standard angular diameter distance formula and other galaxy parameters used in Fukugita and Turner (1991). To find the most adequate flat cosmological model and put a limit on the value of dimensionless cosmological constant
, the mean value of the angular separation of images, probability distribution of angular separation and cumulative probability are calculated for given source and lens redshifts and compared with the observed values through several statistical methods. When there is no angular selection effect, models with highest value of
is preferred generally. When the angular selection effects are considered, the preferred model depends on the shape of the selection functions and statistical methods; yet, models with large
are preferred in general. However, the present data can not rule out any of the flat universe models with enough confidence. This approach can potentially select out best model. But at the moment, we need more data.
THE BVR CCD PHOTOMETRY OF GLOBULAR CLUSTER M13
PYO TAE SOO ; LEE SEE-WOO ;
Journal of The Korean Astronomical Society, volume 27, issue 2, 1994, Pages 119~132
The BVR CCD photometry was performed for the globular cluster M13 down to
over the region from the center to the west 13 arcmin and the CMD of M13 is investigated. The major photometric error in the crowded field which is due to the variation in the sky background was corrected by the median filtering method and the direct sky method. Some characteristics of the CMD of M13 obtained in the present study are as follows: Firstly, the distribution of stars on the CMD is well consistent with the mean lines of Sandage(1970) along the red giant branch(RGB), horizontal branch(HB) and asymtotic giant branch(AGB). Secondly, some gaps exists along the RGB and blue horizontal branch(BHB). Thirdly, the UV-bright stars are more concentrated at the inner region of the cluster.
TIME VARIATION OF SiO (v=1, J=2-1) MASERS OF LONG PERIOD VARIABLES
LEE SANG GAK ; KIM EUNHYEUK ; LEE HYUNG MOK ;
Journal of The Korean Astronomical Society, volume 27, issue 2, 1994, Pages 133~146
We have detected a SiO maser line (v=1, J=2- 1) for 15 stars out of about 80 long period variables in the wide range of period. No new sources are detected; all detected sources are variables with period longer than 300 days; no evidence is found that the dust grains in the outer envelope have influenced on this line. The time variation of this maser line for 7 stars, T Cep,
, U Her, R Leo, R Lmi, U Ori, and R Ser is observed and compared with optical light curve at the same epoch of maser observation. No universial relation between the time variation and the optical light curve is found. It implies that the radiation from a central star does not much play an important role for the direct pumping of the SiO maser line.
A HIGHLY DISTURBED MOLECULAR CLOUD S287: I. CO OBSERVATIONS AND KINEMATICS
LEE YOUNGUNG ;
Journal of The Korean Astronomical Society, volume 27, issue 2, 1994, Pages 147~158
We have obtained high angular resolution maps toward a molecular cloud associated with an HII region S287 and studied mainly kinematics of the cloud. The mapped region is 1.5 square degrees of the cloud in the transitions of
. We have obtained a large range of mass,
using three different techniques. The S287 molecular cloud shows a very disturbed feature: velocity field of the cloud is very complicated, and shows several arcs. It is likely that the southern part of cloud is being disrupted by the residing HII region S287 as well as external perturbing sources. In addition to an HII region, five bipolar outflows are also disturbing the molecular gas significantly. The large virial mass and the very disturbed morphology may reflect the fact that the cloud is not gravitationally bound system, as in the case of nearby giant molecular cloud (GMC) G216-2.5. The several arc structure and the filamentary features are possibly driven by external strong stellar winds, and these external perturbing sources may be driving the second generation of star-forming activities on the edges of the S287 molecular cloud.
A STUDY OF LYNDS 1251 DARK CLOUD: I. STRUCTURE AND KINEMATICS
LEE YOUNGUNG ;
Journal of The Korean Astronomical Society, volume 27, issue 2, 1994, Pages 159~175
We have mapped the whole extent of a dark cloud Lynds 1251 in the emission of the J=1-0 transitions of
using FCRAO's fifteen-beam array receiver in high angular resolution of 50'. We have derived physical parameters of L1251, discussed three different mass estimate techniques, and obtained a large range of mass, 600 to
, depending on the techniques. The factor of 10 discrepancy between the virial and LTE masses is much larger than expected based on the uncertainties residing in two methods. The large virial mass may reflect the fact that L1251 is not gravitationally bound system as in the case of dark clouds in solar neighborhood. Two outflows are affecting the dynamics of cloud significantly but not enough to reshape the whole extent of the cloud. The small cloud, 'Stripe', which is apparently connected with main cloud, is not likely to be associated with L1251. The velocity gradient composed on this small cloud may be driven by other unknown sources. It is found that L1251 cloud itself is very quiescent except the two bipolar outflow regions.
PHOTOMETRIC EVOLUTION OF ELLIPTICAL GALAXIES
JUNG HEE ; LEE SEE-WOO ;
Journal of The Korean Astronomical Society, volume 27, issue 2, 1994, Pages 177~190
We have examined the photometric evolution of elliptical galaxies, using stellar evolutionary models covering the wide ranges of metallicity and mass, and the different IMFs (simple IMP & time-dependent bimodal IMF). The model with a time-dependent bimodal IMF can reproduce the observed integrated magnitudes and colors at all wavelengths. The computed model shows that the star formation in elliptical galaxies is still going on, although the number of newly born stars is very small. The chemical evolutionary effect is clearly seen in the C-M diagram of computed elliptical galaxies.
MAXIMUM POWER ENTROPY METHOD FOR LOW CONTRAST IMAGES
CHAE JONG-CHUL ; YUN HONG SIK ;
Journal of The Korean Astronomical Society, volume 27, issue 2, 1994, Pages 191~201
We propose to use the entropy of power spectra defined in the frequency domain for the deconvolution of extended images. Spatial correlations requisite for extended sources may be insured by increasing the role of power entropy because the power is just a representation of spatial correlations in the frequency domain. We have derived a semi-analytical solution which is found to severely reduce computing time compared with other iteration schemes. Even though the solution is very similar to the well-known Wiener filter, the regularizingng term in the new expression is so insensitive to the noise characteristics as to assure a stable solution. Applications have been made to the IRAS
images of the dark cloud B34 and the optical CCD image of a solar active region containing a circular sunspot and a small pore.