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- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 70/123
691
- 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.
692
- 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.
693
- 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.
694
- 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.
695
- 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.
696
- 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.
697
A NEW CHANNEL TO SEARCH FOR EXTRA-SOLAR SYSTEMS WITH MULTIPLE PLANETS VIA GRAVITATIONAL MICROLENSING
- HAN CHEONGHO
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.35-40
- 2002
- 원문 바로보기
Gaudi, Naber & Sackett pointed out that if an event is caused by a lens system containing more than two planets, all planets will affect the central region of the magnification pattern, and thus the existence of the multiple planets can be inferred by detecting additionally deformed anomalies from intensive monitoring of high magnification microlensing events. Unfortunately, this method has important limitations in identifying the existence of multiple planets and determining their parameters (the mass ratio and the instantaneous projected separation) due to the degeneracy of the resulting light curve anomalies from those induced by a single planet and the complexity of multiple planet lensing models. In this paper, we propose a new channel to search for multiple planets via microlensing. The method is based on the fact that the lensing light curve anomalies induced by multiple planets are well approximated by the superposition of those of the single planet systems where the individual planet-primary pairs act as independent lens systems. Then, if the source trajectory passes both of the outer deviation regions induced by the individual planets, one can unambiguously identify the existence of the multiple planets. We illustrate that the probability of successively detecting light curve anomalies induced by two Jovian-mass planets located in the lensing zone through this channel will be substantial. Since the individual anomalies can be well described by much simpler single planet lensing models, the proposed method has an important advantage of allowing one to accurately determine the parameters of the individual planets.
698
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 35, n.1
- pp.29-34
- 2002
- 원문 바로보기
We have conducted UBVI CCD photometry of an intermediate-age open cluster NGC 559 to investigate the effect of dynamical evolution on the stellar distributions in NGC 559. Our photometry allows better estimates of distance and age of the cluster owing to much deeper photometry (V <TEX>$\le$</TEX> 21) than previous ones. It is found that the luminosity function and mass function as well as the spatial stellar distributions are affected by the dynamical evolution. Mass segregation leads to the central concentration of the high mass stars, which results in the flattened mass function inside the half mass radius.
699
- LEE SUNGHO
- Journal of the Korean astronomical society = 천문학회지
- 35, n.3
- pp.111-121
- 2002
- 원문 바로보기
We have measured the correlation functions of the optically selected clusters of galaxies in the Abell and the APM catalogs, and of the X-ray clusters in the X-ray-Brightest Abell-type Clusters of galaxies (XBACs) catalog and the Brightest Clusters Sample (BCS). The same analysis method and the same method of characterizing the resulting correlation functions are applied to all observational samples. We have found that the amplitude of the correlation function of the APM clusters is much higher than what has been previously claimed, in particular for richer subsamples. The correlation length of the APM clusters with the richness R <TEX>$\ge$</TEX> 70 (as defined by the APM team) is found to be <TEX>$r_0 = 25.4_{-3.0}^{+3.1}\;h^{-1}$</TEX> Mpc. The amplitude of correlation function is about 2.4 times higher than that of Croft et al. (1997). The correlation lengths of the Abell clusters with the richness class RC <TEX>$\ge$</TEX> 0 and 1 are measured to be <TEX>$r_0 = 17.4_{-1.1}^{+1.2}$</TEX> and <TEX>$21.0_{-2.8}^{+2.8}\;h^{-1}$</TEX> Mpc, respectively, which is consistent with our results for the APM sample at the similar level of richness. The richness dependence of cluster correlations is found to be <TEX>$r_0= 0.40d_c + 3.2$</TEX> where <TEX>$d_c$</TEX> is the mean intercluster separation. This is identical in slope with the Bahcall & West (1992)'s estimate, but is inconsistent with the weak dependence of Croft et al. (1997). The X-ray bright Abell clusters in the XBACs catalog and the X-ray selected clusters in the BCS catalog show strong clustering. The correlation length of the XBACs clusters with <TEX>$L_x {\ge}0.65{\times} 10^{44}\;h^{-2}erg\;s^{-1}$</TEX> is <TEX>$30.3_{-6.5}^{+8.2}\;h^{-1}$</TEX> Mpc, and that of the BCS clusters with <TEX>$L_x {\ge}0.70{\times} 10^{44}\;h^{-2}erg\;s^{-1}$</TEX> is <TEX>$30.2_{-8.9}^{+9.8}\;h^{-1}$</TEX> Mpc. The clustering strength of the X-ray clusters is much weaker than what is expected from the optical clusters.
700
- LEE C.-W.
- Journal of the Korean astronomical society = 천문학회지
- 34, n.2
- pp.111-117
- 2001
- 원문 바로보기
Recently, we have set up a new digital CCD camera system, MicroMax YHS-1300 manufactured by Roper Scientific for Ha observation by Solar Flare Telescope at Bohyunsan Optical Astronomy Observatory. It has a 12 bit dynamic range, a pixel number of 1300<TEX>$\times$</TEX>1030, a thermoelectric cooler, and an electric shutter. Its readout speed is about 3 frames per second and the dark current is about 0.05 e-/p/s at <TEX>$-10^{\circ}C$</TEX>. We have made a system performance test by confirming the system linearity, system gain, and system noise that its specification requires. We have also developed a data acquisition software which connects a digital camera con-troller to a PC and acquires H<TEX>$\alpha$</TEX> images via Microsoft Visual C++ 6.0 under Windows 98. Comparisons of high quality H<TEX>$\alpha$</TEX> images of AR 9169 and AR 9283 obtained from SOFT with the corresponding images from Learmonth Solar Observatory in Australia confirm that our H<TEX>$\alpha$</TEX> digital observational system is performed properly. Finally, we present a set of H<TEX>$\alpha$</TEX> images taken from a two ribbon flare occurred in AR 9283.