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1968년 ~ 2025년까지 1,227 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 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 33/123
321
- Deng, Xin-Fa
- Journal of the Korean astronomical society = 천문학회지
- 45, n.3
- pp.59-64
- 2012
- 원문 바로보기
Using the volume-limited Main galaxy sample constructed from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we explore the environmental dependence of the fraction of 'unconventional' galaxies: luminous blue and faint red. It is found that the fraction of faint red increases apparently with increasing local density, and the fraction of luminous blue declines substantially with increasing local density, which shows that there is an environmental dependence for color beyond that for luminosity.
322
- Lee, Sung Hwan
- Journal of the Korean astronomical society = 천문학회지
- 45, n.5
- pp.111-116
- 2012
- 원문 바로보기
We present a mathematical model that predicts the variation of illuminance during a solar eclipse, considering continuous effects of limb darkening. We assume that (1) the Sun and the Moon constitute perfect spheres, (2) the Moon crosses the Sun with a constant apparent velocity, and (3) sunspots, prominences, and coronae can be neglected. We compare predictions of this model with actual measurements made by M<TEX>$\ddot{o}$</TEX>llmann & Vollmer (2006) during a total solar eclipse in Turkey, and with predictions of existing models. The new model is shown to describe the actual phenomenon more accurately than existing models.
323
- Feng, Song
- Journal of the Korean astronomical society = 천문학회지
- 45, n.6
- pp.167-173
- 2012
- 원문 바로보기
Inter-granular Bright Points (igBPs) are small-scale objects in the Solar photosphere which can be seen within dark inter-granular lanes. We present a new algorithm to automatically detect and extract igBPs. Laplacian and Morphological Dilation (LMD) technique is employed by the algorithm. It involves three basic processing steps: (1) obtaining candidate 'seed' regions by Laplacian; (2) determining the boundary and size of igBPs by morphological dilation; (3) discarding brighter granules by a probability criterion. For validating our algorithm, we used the observed samples of the Dutch Open Telescope (DOT), collected on April 12, 2007. They contain 180 high-resolution images, and each has a <TEX>$85{\times}68\;arcsec^2$</TEX> field of view (FOV). Two important results are obtained: first, the identified rate of igBPs reaches 95% and is higher than previous results; second, the diameter distribution is <TEX>$220{\pm}25km$</TEX>, which is fully consistent with previously published data. We conclude that the presented algorithm can detect and extract igBPs automatically and effectively.
324
- Choi, Min-Ho
- Journal of the Korean astronomical society = 천문학회지
- 44, n.5
- pp.201-208
- 2011
- 원문 바로보기
The NGC 1333 IRAS 4B region is observed in the 6.9 mm and 1.3 cm continuum with an angular resolution of about 0.4 arcseconds. IRAS 4BI is detected in both bands, and BII is detected in the 6.9 mm continuum only. The 1.3 cm source of BI seems to be a disk-like flattened structure with a size of about 50 AU. IRAS 4BI does not show any sign of multiplicity. Examinations of archival infrared images show that the dominating emission feature in this region is a bright peak in the southern outflow driven by BI, corresponding to the molecular hydrogen emission source HL 9a. Both BI and BII are undetectable in the mid-IR bands. The upper limit on the far-IR flux of IRAS 4BII suggests that it may be a very low luminosity young stellar object.
325
- Choi, Isaac Yeoun-Gyu
- Journal of the Korean astronomical society = 천문학회지
- 44, n.5
- pp.161-175
- 2011
- 원문 바로보기
We examine the dependence of the morphology of spiral galaxies on the environment using the KIAS Value Added Galaxy Catalog (VAGC) which is derived from the Sloan Digital Sky Survey (SDSS) DR7. Our goal is to understand whether the local environment or global conditions dominate in determining the morphology of spiral galaxies. For the analysis, we conduct a morphological classification of galaxies in 20 X-ray selected Abell clusters up to z~0.06, using SDSS color images and the X-ray data from the Northern ROSAT All-Sky (NORAS) catalog. We analyze the distribution of arm classes along the clustercentric radius as well as that of Hubble types. To segregate the effect of local environment from the global environment, we compare the morphological distribution of galaxies in two X-lay luminosity groups, the low-<TEX>$L_x$</TEX> clusters (<TEX>$L_x$</TEX> < <TEX>$0.15{\times}10^{44}$</TEX>erg/s) and high-<TEX>$L_x$</TEX> clusters (<TEX>$L_x$</TEX> > <TEX>$1.8{\times}10^{44}$</TEX>erg/s). We find that the morphology-clustercentric relation prevails in the cluster environment although there is a brake near the cluster virial radius. The grand design arms comprise about 40% of the cluster spiral galaxies with a weak morphology-clustercentric radius relation for the arm classes, in the sense that flocculent galaxies tend to increase outward, regardless of the X-ray luminosity. From the cumulative radial distribution of cluster galaxies, we found that the low-<TEX>$L_x$</TEX> clusters are fully virialized while the high-<TEX>$L_x$</TEX> clusters are not.
326
- Lee, Hee-Won
- Journal of the Korean astronomical society = 천문학회지
- 44, n.2
- pp.59-65
- 2011
- 원문 바로보기
A small number of active galactic nuclei are known to exhibit prominent double peak emission profiles that are well-fitted by a relativistic accretion disk model. We develop a Monte Carlo code to compute the linear polarization of a double peaked broad emission line arising from Thomson scattering. A Keplerian accretion disk is adopted for the double peak emission line region and the geometry is assumed to be Schwarzschild. Far from the accretion disk where flat Minkowski geometry is appropriate, we place an azimuthally symmetric scattering region in the shape of a spherical shell sliced with <TEX>${\Delta}{\mu}=0.1$</TEX>. Adopting a Monte Carlo method we generate line photons in the accretion disk in arbitrary directions in the local rest frame and follow the geodesic paths of the photons until they hit the scattering region. The profile of the polarized flux is mainly determined by the relative location of the scattering region with respect to the emission source. When the scattering region is in the polar direction, the degree of linear polarization also shows a double peak structure. Under favorable conditions we show that up to 0.6% linear polarization may be obtained. We conclude that spectropolarimetry can be a powerful probe to reveal much information regarding the accretion disk geometry of these active galactic nuclei.
327
- Suh, Kyung-Won
- Journal of the Korean astronomical society = 천문학회지
- 44, n.1
- pp.13-21
- 2011
- 원문 바로보기
We model dust around Herbig Ae/Be stars using a radiative transfer model for multiple isothermal circumstellar dust shells to reproduce the multiple broad peaks in their spectral energy distributions (SEDs). Using the opacity functions for various types of dust grains at different temperatures, we calculate the radiative transfer model SEDs for multiple dust shells. For eight sample stars, we compare the model results with the observed SEDs including the Infrared Space Observatory (ISO) and AKARI data. We present model parameters for the best fit model SEDs that would be helpful to understand the overall structure of dust envelopes around Herbig Ae/Be stars. We find that at least four separate dust components are required to reproduce the observed SEDs. For all the sample stars, two innermost dust components (a hot component of 1000-1500 K and a warm component of 300-600 K) with amorphous silicate and carbon grains are needed. Crystalline dust grains (corundum, forsterite, olivine, and water ice) are needed for some objects. Some crystalline dust grains exist in cold regions as well as in hot inner shells.
328
- Lim, Beom-Du
- Journal of the Korean astronomical society = 천문학회지
- 44, n.2
- pp.39-48
- 2011
- 원문 바로보기
UBV I CCD photometry of NGC 2353 is performed as a part of the 'Sejong Open cluster Survey' (SOS). Using photometric membership criteria we select probable members of the cluster. We derive the reddening and distance to the cluster, i.e., E(B - V ) = 0.10 <TEX>${\pm}$</TEX> 0.02 mag and 1.17 <TEX>${\pm}$</TEX> 0.04 kpc, respectively. We find that the projected distribution of the probable members on the sky is elliptical in shape rather than circular. The age of the cluster is estimated to be log(age)=8.1 <TEX>${\pm}$</TEX> 0.1 in years, older than what was found in previous studies. The minimum value of binary fraction is estimated to be about 48 <TEX>${\pm}$</TEX> 5 percent from a Gaussian function fit to the distribution of the distance moduli of the photometric members. Finally, we also obtain the luminosity function and the initial mass function (IMF) of the probable cluster members. The slope of the IMF is <TEX>${\Gamma}=-1.3{\pm}0.2$</TEX>.
329
- Ryu, Jin-Hyuk
- Journal of the Korean astronomical society = 천문학회지
- 44, n.5
- pp.177-193
- 2011
- 원문 바로보기
We present a photometric study of five open clusters (Czernik 5, Alessi 53, Berkeley 49, Berkeley 84, and Pfleiderer 3) in the Sloan Digital Sky Survey. The position and size of these clusters are determined using the radial number density profiles of the stars, and the member stars of the clusters are selected using the proper motion data in the literature. We estimate the reddening, distance and age of the clusters based on the isochrone fitting in the color-magnitude diagram. The foreground reddenings for these clusters are estimated to be E(B - V ) = 0.71 - 1.55 mag. The distances to these clusters are derived to be 2.0 - 4.4 kpc, and their distances from the Galactic center range from 7.57 kpc to 12.35 kpc. Their ages are in the range from 250 Myr to 1 Gyr. Berkeley 49 and Berkeley 84 are located in the Orion spur, Czernik 5 is in the Perseus arm, and Pfleiderer 3 and Alessi 53 are located beyond the Perseus arm.
330
- Kim, Eun-Bin
- Journal of the Korean astronomical society = 천문학회지
- 44, n.4
- pp.115-123
- 2011
- 원문 바로보기
To perform imaging observations of optically red objects such as high redshift quasars and brown dwarfs, the Center for the Exploration of the Origin of the Universe (CEOU) recently developed an optical CCD camera, Camera for QUasars in EArly uNiverse (CQUEAN), which is sensitive at 0.7-1.1 <TEX>${\mu}m$</TEX>. To enable observations with long exposures, we develop an auto-guiding system for CQUEAN. This system consists of an off-axis mirror, a baffle, a CCD camera, a motor and a differential decelerator. To increase the number of available guiding stars, we design a rotating mechanism for the off-axis guiding camera. The guiding field can be scanned along the 10 arcmin ring offset from the optical axis of the telescope. Combined with the auto-guiding software of the McDonald Observatory, we confirm that a stable image can be obtained with an exposure time as long as 1200 seconds.