모달창 닫기
- 홈으로 이동
1968년 ~ 2024년까지 1,211 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 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 68/122
671
- OH SU YEON
- Journal of the Korean astronomical society = 천문학회지
- 35, n.3
- pp.151-157
- 2002
- 원문 바로보기
From the data of solar wind observation by ACE spacecraft orbiting the Earth-Sun Lagrangian point, we selected 48 forward interplanetary shocks(IPSs) occurred in 2000, maximum solar activity period. Examining the profiles of solar wind parameters, the IPSs are classified by their shock drivers. The significant shock drivers are the interplanetary coronal mass ejection(ICME) and the high speed stream(HSS). The IPSs driven by the ICMEs are classified into shocks driven by magnetic clouds and by ejectas based on the existence of magnetic flux rope structure and magnetic field strength. Some IPSs could be formed as the blast wave by the smaller energy and shorter duration of shock drivers such as type II radio burst. Out of selected 48 forward IPSs, <TEX>$56.2\%$</TEX> of the IPSs are driven by ICME, <TEX>$16.7\%$</TEX> by HSS, and <TEX>$16.7\%$</TEX> of the shocks are classified into blast-wave type shocks. However, the shock drivers of remaining <TEX>$10\%$</TEX> of the IPSs are unidentified. The classification of the IPSs by their driver is a first step toward investigating the critical magnitudes of the IPS drivers commencing the magnetic storms in each class.
672
- LEE CHANG WON
- Journal of the Korean astronomical society = 천문학회지
- 35, n.4
- pp.187-196
- 2002
- 원문 바로보기
A spectral line survey is performed from 159.7 to 164.7 GHz toward Orion-KL, as an extension of our previous line survey from 138.3 to 150.7 GHz with the same 14 m radio telescope of Taeduk Radio Astronomy Observatory. Typical system temperatures were 260 - 1000 K to achieve a sensitivity of about 0.02 - 0.04 K in TA unit. A total of 63 line spectra are detected in this survey. Among them, 54 lines lines are found to be the first detections towards an astronomical source and only 9 spectral lines have been previously identified from other observations. Forty-eight of 54 lines are believed to be from the known transitions of the known molecules, while 6 lines are 'unidentified'. All detected lines are found to be from a total of 10 molecular species and their isotopic variants. The molecular species with most numerous detected transitions are <TEX>$HCOOCH_3$</TEX> (22), followed by <TEX>$CH_3OCH_3$</TEX> (7), <TEX>$C_2H_5CN$</TEX> (7), and <TEX>$SO_2$</TEX> (6). The LTE rotation diagram analysis using all homogeneous data with those from previous survey gives more reliable determination of physical quantities. The derived values of the rotation temperatures and column densities for <TEX>$HCOOCH_3$</TEX>, <TEX>$CH_3OCH_3$</TEX>, and <TEX>$SO_2$</TEX> are are 75 <TEX>$\~$</TEX> 197 K and <TEX>$1.5 {\~}18 {\times} 10^{15}\;cm^{-2}$</TEX>, respectively.
673
- KIM SANG CHUL
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.9-28
- 2002
- 원문 바로보기
We present UBVI CCD photometry of the stellar contents and globular cluster(GC) candidates in the spiral galaxy NGC 300 in the Sculptor group. Color-magnitude diagrams for 18 OB associations having more than 30 member stars are presented. The slope of the initial mass function for the bright stars in NGC 300 is estimated to be <TEX>${\Gamma}= -2.6{\pm} 0.3$</TEX>. Assuming the distance to NGC 300 of (m - M)o = 26.53 <TEX>$\pm$</TEX> 0.07, the mean absolute magnitude of three brightest blue stars is obtained to be < <TEX>$M_v^{BSG}$</TEX> (3) > = -8.95 mag. We have performed search for GCs in NGC 300 and have found 17 GC candidates in this galaxy. Some characteristics of these GC candidates are discussed.
674
- CHANG HEON-YOUNG
- Journal of the Korean astronomical society = 천문학회지
- 35, n.3
- pp.123-130
- 2002
- 원문 바로보기
An elliptical accretion disk may be formed by tidally disrupted debris of a flying-by star in an active galactic nucleus (AGN) or by tidal perturbation due to a companion in a binary black hole system. We investigate the iron K<TEX>$\alpha$</TEX> line profiles expecting from a geometrically thin, relativistic, elliptical disk in terms of model parameters, and find that a broad and skewed line profile can be reproduced well. Its shape is variable to the model parameters, such as, the emissivity power-law index, the ellipticity of the disk, and the major axis orientation of the elliptical accretion disk. We suggest that our results may be useful to search for such an elliptical disk and consequently the tidal disruption event.
675
- KIM KANG-MIN
- Journal of the Korean astronomical society = 천문학회지
- 35, n.4
- pp.221-227
- 2002
- 원문 바로보기
Cassegrain interface module (CIM) of the fiber-fed high resolution echelle spectrograph has been designed and manufactured for the 1.8 m reflector at the Bohynsan Optical Astronomy Observatory. We also constructed a long slit spectrograph attached to this CIM, which would replace the earlier rather inefficient medium dispersion spectrometer. We present detailed description for design and manufacturing concepts of the CIM which consists of a slit assembly, slit monitoring system, calibration lamp system and a long slit spectrograph, in order to provide how the overall system and each part. are constructed. The preliminary performance test carried out so far seems to indicate a successful result.
676
- PARK BYEONG-GON
- Journal of the Korean astronomical society = 천문학회지
- 35, n.4
- pp.197-208
- 2002
- 원문 바로보기
Five contemporary pre-main sequence (PMS) evolution model grids are compared with the photo-metric data for a nearly complete sample of low-mass members in NGC 2264. From amongst the grids compared, the models of Baraffe et al. (1998) prove to be the most reliable in mass-age distribution. To overcome the limited mass range of the models of Baraffe et al. we derived a simple transformation relation between the mass of a PMS star from Swenson et al. (1994) and that from Baraffe et al., and applied it to the PMS stars in NGC 2264 and the Orion nebula cluster (ONC). The resulting initial mass function (IMF) of the ONC shows that the previous interpretation of the IMF is not a real feature, but an artifact caused by the evolution models adopted. The IMFs of both clusters are in a good agreement with the IMF of the field stars in the solar neighborhood. This result supports the idea proposed by Lada, Strom, & Myers (1993) that the field stars originate from the stars that are formed in clusters and spread out as a result of dynamical dissociation. Nevertheless, the IMFs of OB associations and young open clusters show diverse behavior. For the low-mass regime, the current observations suffer from difficulties in membership assignment and sample incompleteness. From this, we conclude that a more thorough study of young open clusters is necessary in order to make any definite conclusions on the existence of a universal IMF.
677
- LEE Ho-GYU
- Journal of the Korean astronomical society = 천문학회지
- 35, n.2
- pp.105-110
- 2002
- 원문 바로보기
We present the results of VLA <TEX>$NH_3$</TEX> (1,1) and (2,2) line observations of the young-stellar object (YSO) IRAS 19550+3248. The integrated intensity map of the <TEX>$NH_3$</TEX> (1,1) line shows that there are two ammonia cores in this region; core A which is associated with the YSO, and core B which is diffuse and located at the northeast of core A. Core A is compact and elongated along the east-west direction (0.07 pc<TEX>$\times$</TEX>0.05 pc) roughly perpendicular to the molecular outflow axis. Core B is diffuse and extended (0.18 pc<TEX>$\times$</TEX>0.07 pc). <TEX>$NH_3$</TEX> (2,2) line is detected only toward core A, which indicates that it is hotter (~ 15 K), presumably due to the heating by the YSO. The <TEX>$NH_3$</TEX> (1,1) line toward core A is wide (<TEX>${\Delta}v{\ge} 3 km s^{-l}$</TEX>) and appears to have an anomalous intensity ratio of the inner satellite hyperfine lines. The large line width may be attributed to the embedded YSO, but the hyperfine anomaly is difficult to explain. We compare the results of <TEX>$NH_3$</TEX> observations with those of previous CS observations and find that the CS emission is detected only toward core A and is much more extended than the <TEX>$NH_3$</TEX> emission.
678
- AHN SANG-HYEON
- Journal of the Korean astronomical society = 천문학회지
- 35, n.4
- pp.175-185
- 2002
- 원문 바로보기
Almost half of primeval galaxies show P-Cygni type profiles in the Ly<TEX>$\alpha$</TEX> emission line. The main underlying mechanism for the profile formation in these systems is thought to be the frequency re-distribution of the line photons in expanding scattering media surrounding the emission source. A Monte Carlo code is developed to investigate the Ly<TEX>$\alpha$</TEX> line transfer in an optically thick and moving medium with a careful consideration of the scattering in the damping wings. Typical column densities and expansion velocities of neutral hydrogen investigated in this study are <TEX>$N_{H1}{\~}10^{17-20}\;cm^{-2}$</TEX> and <TEX>${\Delta}V{\~} 100 km\;s^{-1}$</TEX>. We investigate the dependence of the emergent profiles on the kinematics and on the column density. Our numerical results are applied to show that the damped Ly<TEX>$\alpha$</TEX> absorbers may possess an expanding H I supershell with bulk flow of <TEX>${\~}200 km\;s^{-l}$</TEX> and H I column density <TEX>$N_{H1}{\~}10^{19}\;cm^{-2}$</TEX>. We briefly discuss the observational implications.
679
- PARK CHAN-GYUNG
- Journal of the Korean astronomical society = 천문학회지
- 35, n.2
- pp.67-73
- 2002
- 원문 바로보기
We have made a topological study of cosmic microwave background (CMB) polarization maps by simulating the AMiBA experiment results. A ACDM CMB sky is adopted to make mock interferometric observations designed for the AMiBA experiment. CMB polarization fields are reconstructed from the AMiBA mock visibility data using the maximum entropy method. We have also considered effects of Galactic foregrounds on the CMB polarization fields. The genus statistic is calculated from the simulated Q and U polarization maps, where Q and U are Stokes parameters. Our study shows that the Galactic foreground emission, even at low Galactic latitude, is expected to have small effects on the CMB polarization field. Increasing survey area and integration time is essential to detect non-Gaussian signals of cosmological origin through genus measurement.
680
- CHOI CHUL-SUNG
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.1-7
- 2002
- 원문 바로보기
We have studied the long-term X-ray light curve (2-10 keV) of the luminous Seyfert 1 galaxy MCG-2-58-22 by compiling data, from various X-ray satellites, which together cover more than 20 years. We have found two distinct types of time variations in the light curve. One is a gradual and secular decrease of the X-ray flux, and the other is the episodic increase of X-ray flux (or flare) by a factor of 2-4 compared with the level expected from the secular variation. We detected 3 such flares in total; a representative duration for the flares is <TEX>$\~$</TEX>2 years, with intervening quiescent intervals lasting <TEX>$\~$</TEX>6-8 years. We discuss a few possible origins for these variabilities. Though a standard disk instability theory may explain the displayed time variability in the X-ray light curve, the subsequent accretions of stellar debris, from a tidal disruption event caused by a supermassive black hole in MCG-2-58-22, cannot be ruled out as an alternative explanation.