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1968년 ~ 2023년까지 1,187 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 102/119
1011
- YUN HONG SIK
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.89-98
- 1993
- 원문 바로보기
Magnetostatic models of starspots of late type main sequence stars<TEX>$(G5V\~K5V)$</TEX> have been constructed to investigate their physical characteristics by using the similarity law suggested by Schluter and Temesvary(1958) and later employed by Deinzer(1965) and Yun(1968). The starspots are assumed to be single, circular and in horizontal magnetostatic equilibrium. In the present study we considered only those model spots whose area covers less than <TEX>$12\%$</TEX> of the entire stellar surface as suggested by observations. The computed surface field strength of our model spots ranges from <TEX>$10^3$\;to\;several\;10^3$</TEX> gauss and their magnetic flux is found to be <TEX>$10\~100$</TEX> times that of sunspots. The field strength is sensitive to spectral type, which increases with later spectral type. In contrast to the field strength, the area of starspots depends strongly on the total magnetic flux. Finally, it is noted that the computed field strength of model spots belonging to <TEX>$G0V\~G5V$</TEX> falls below the equipartition field strength at their parent stellar surface unless the coverage is less than <TEX>$2\%$</TEX>. This suggests that the observed spot on <TEX>$G0V\~G5V$</TEX> stars is likely to be a group of small starspots.
1012
- KIM CHULHEE
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.115-134
- 1993
- 원문 바로보기
The light curve and radial velocity curve of multiperiodic dwarf cepheid VI719 Cyg (HD200925) with peculiar light curve have been reanalyzed in order to identify the oscillation modes to confirm the helium settling within the envelope. To do these, through the period search for the photometric and radial velocity data from the literature, two different periods were determined and the oscillation modes corresponding to the first and second periods were identified as the fundamental and first radial overtones. Hence the helium settling within the envelope was confirmed from the period ratio. The color excess, metallicity, effective temperature, and surface gravity corresponding to two different modes were determined and it was found that these parameters almost do not depend upon different oscillation mode. By utilizing the surface brightness method, we investigated the variation of angular diameter and radial displacement and it was found that the angular variation is very peculiar. Also by referring to the stellar models, mass and age were determined as <TEX>$2.7M_{\bigodot}$</TEX> and 0.42 Gyr respectively which make this variable star heavier and younger than other multimode dwarf cepheids. Preliminary spectroscopic CCD observations were carried out and it was found that Mg in VI719 Cygni is nearly solar abundent according to the analysis of <TEX>$5172.68{\AA}MgI$</TEX> line which is inconsistent with the photometric result. It was suggested that VI719 Cyg may be classified as a <TEX>$\rho$</TEX> Pup stars according to the photometric characteristics.
1013
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.13-32
- 1993
- 원문 바로보기
We have conducted BVI photographic surface photometry of four spiral galaxies NGC1087, NGC2715, NGC2844 and NGC3593, by making use of the Kiso Schmidt plates. Detailed examination of the morphological properties of the galaxies using isophotal maps and luminosity profiles showed that all the program galaxies have some peculiarities in their luminosity distributions. NGC1087 and NGC2715 have extremely small nuclei with inner rings which contain several bright HII regions. NGC2844 has a very large bulge whose luminosity dominates over the disk luminosity in all the radii. The I-band luminosity profile of NGC3593 shows shallower gradient than B- and V-band profiles. We were able to successfully decompose the luminosity profile into a bulge following de Vaucouleurs <TEX>$\gamma^{1/4}-law$</TEX> and an exponential disk only for NGC 3953. Other galaxies have more complicated luminosit profiles.
1014
- KIL HYO SUB
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.103-114
- 1993
- 원문 바로보기
We have analyzed a set of high resolution photographic line profiles of a Zeeman sensitive Fe I <TEX>$\lambda$</TEX> 6302.5 line taken with the Universal Birefringent Filter over a single round sunspot (SPO 5007) at the Sacramento Peak Solar Observatory. The observed spectra recorded on films are traced by PDS and the traced densities are converted to relative intensity by means of IRAF. The Stokes I and V profiles are then constructed by adding together and subtracting from each other the left and right handed circular polarizations, respectively. The reduced I and V profiles are analyzed by means of the coarse analysis(Auer et al.(1977), Skumanich and Lites(1987)) with the use of inversion technique. It is found that the umbral field strength is about 3000 gauss and the field distribution follows closely the emperical model proposed by Wittmann(1974).
1015
- LEE SEE-WOO
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.47-64
- 1993
- 원문 바로보기
The photometric evolution of cluster stars are examined for six synthetic clusters in the age range from <TEX>$2.4\times10^6\;yr\;to\;7.6\times10^8yr$</TEX> by using the detailed evolutionary model calculation, and their results are compared with the observed integrated absolute magnitude and colors of 47 clusters. The reasonable agreements of the observed photometric parameters with the synthetic evolutionary sequences imply that there is a general form of time-dependent IMF including the noncoeval formation of stars and its detailed function is changed slightly with various environmental conditions of each primordial cloud.
1016
- CHOI JEONG TAE
- Journal of the Korean astronomical society = 천문학회지
- 26, n.1
- pp.33-45
- 1993
- 원문 바로보기
We have conducted surface photometry of a spiral galaxy NGC4419, by making use of photographic plates in U, B, V and R-bands taken by 105cm Schmidt Camera at Kiso Observatory. Two dimensional surface brightness distributions as well as luminosity profiles along the major axis are examined in detail to decipher the morphological properties of the galaxy. Analysis of the color distributions of NGC4419 shows that B-V and U-B colors remain constant throughout the galaxy with a weak trend of blue bulge in B-V color. The blue bulge might indicate an active star formation in the nucleus of NGC4419. For a quantitative analysis of the luminosity distribution of NGC4419, the observed luminosity profiles are decomposed into bulge and disk components, assuming the bulge component to follow de Vaucouleurs <TEX>$\gamma^{1/4}-law$</TEX> while the disk component is assumed to be exponential. The fitting generally fails at the central part and at the shoulder near r = 15' where bulge and disk components overlap. The failure at the central part cannot be attributed wholly by the seeing disk since the core-radius of the central plateau is much larger than the width of point spread function. The failure at shoulder could be due to the luminosities from the spiral arms.
1017
- MINH Y. C.
- Journal of the Korean astronomical society = 천문학회지
- 26, n.2
- pp.99-101
- 1993
- 원문 바로보기
We have searched for the 2 mm transitions of <TEX>$H_2COH^+(2_{02}-1_{01})$</TEX> and <TEX>$H_2\;^{13}CO(2_{02} - 1_{01},\; 2_{12}-1_{11},\;and\;2_{11}-1_{10})$</TEX> toward the dense interstellar molecular clouds Orion A, TMC-1 and L134N using the FCRAO 14 m telescope. None of the transitions have been detected except the <TEX>$H_2\;^{13}CO$</TEX> transitions toward Orion-KL. We set upper limits for the abundances of the protonated formaldehyde ion <TEX>$(H_2COH^+)$</TEX>, which are close to the abundances expected from ion-molecule chemistry.
1018
- Lee, Hyung-Mok
- 天文學會誌 = The journal of the Korean Astronomical Society
- 25, n.2
- pp.111-128
- 1992
- 원문 바로보기
Infrared emissions from spherical dust, clouds are calculated using quasi-diffusion method. We have employed graphite-silicate mixture with power-law size distribution for the dust model. The grains are assumed to be heated and cooled by radiative processes only. The primary heating source is diffuse interstellar radiation field. hut the cases with an embedded source are also considered. Since graphite grains have higher temperature than silicate grains, the observed IR emission is mainly due to graphite grains, unless the fraction of graphite grains is negligibly small. The color temperature of Bok globules obtained from IRAS 60 and <TEX>$100{\mu}m$</TEX> data are found to be consistent with the dust cloud with graphite-silicate mixture exposed to average interstellar radiation field. The color temperature is sensitive to the external radiation field, but rather insensitive to the size distribution of the grains. We found that the density distribution can be recovered outside the beam size using the inversion technique that assumes negligible optical depth. However, the information within the beam size is lost for if beam convolved intensity distributions are used in deriving density profile.
1019
- Hong, S.S.
- 天文學會誌 = The journal of the Korean Astronomical Society
- 25, n.1
- pp.23-46
- 1992
- 원문 바로보기
The electrical, mechanical and optical capabilities have been tested of the microdensitometer PDS 1010GMS at the Korea Astronomy Observatory. The highest stage of scan speed 255 csu (conventional speed unit) is measured to be 47 mm/s. At this speed the position is displaced by <TEX>$4{\mu}m$</TEX> to the direction of scanning and the density is underestimated by <TEX>$0.4{\sim}0.7D$</TEX>. Standard deviation in the measured density is proportional to <TEX>$A^{-0.46}$</TEX>, where A is the area of scan aperture. The accuracy of position repeatability is <TEX>${\pm}1{\mu}m$</TEX>, and that of density repeatability is <TEX>${\pm}(0.003{\sim}0.03)D$</TEX>. Callier coefficient is determined to be 1.37; the semispecular density is directly proportional to the diffuse density up to 3.5D. Because the logarithmic amplifier has a finite response time, the densities measured at high scan speeds are underestimated to the degree that speeds higher than 200 csu are inadequate for making an accurate astronomical photometry. After power is on, an about 5 hour period of warming is required to stabilize the system electrically and mechanically as well. On the basis of this performance test, we have determined the followings as the optimum scan parameters for the astronomical photometry: For the scan aperture <TEX>$10\;\sim\;20{\mu}m$</TEX> is optimal, and for the scan speed. <TEX>$20\;{\sim}\;50$</TEX> csu is appropriate. These parameter values are chosen in such a way that they may keep the density repeatability within <TEX>${\pm}0.01D$</TEX>, the position displacement under <TEX>$1{\mu}m$</TEX>, and the density underestimation below 0.1D even in high density regions.
1020
BLUE STRAGGLERS, CATACLYSMIC VARIABLES, X-RAY BINARIES, AND MILLISECOND PULSARS IN GLOBULAR CLUSTERS
- Lee, Hyung-Mok
- 天文學會誌 = The journal of the Korean Astronomical Society
- 25, n.1
- pp.47-64
- 1992
- 원문 바로보기
Cores of globular clusters are an ideal place for close encounters between stars. The outcome of tidal capture can be stellar mergers, close binaries between normal stars (W UMa type), cataclysmic variables composed of white dwarf and normal star pairs, or low-mass X-ray binaries consisting of a neutron star and a normal star pairs. Stellar mergers can be the origin of blue stragglers in dense globular clusters although they are hard to observe. Low mass X-ray binaries would eventually become binary pulsars with short pulse periods after the neutron stars accrete sufficient amount of matter from the companion. However, large number of recently discovered, isolated millisecond pulsars (as opposed to binary pulsars) in globular clusters may imply that they do not have to gain angular speeds during the X-ray binary phase. We propose that these isolated millisecond pulsars may have formed through the disruptive encounters, which lead to the formation of accretion disk without Roche lobe filling companion, between a neutron star and a main-sequence star. Based on recently developed multicomponent models for the dynamical evolution of globular clusters, we compute the expected numbers of various systems formed by tidal capture as a function of time.