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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 30/119
291
- Lee, Jeong-Eun
- Journal of the Korean astronomical society = 천문학회지
- 44, n.2
- pp.67-72
- 2011
- 원문 바로보기
We report the results of our high resolution optical spectroscopic monitoring campaign (<TEX>${\lambda}$</TEX> = 3800 ~ 8800 <TEX>${\AA}$</TEX>, R = 30000 - 45000) of the new FU Orionis-type object HBC 722. We observed HBC 722 with the BOES 1.8-m telescope between November 26 and December 29, 2010, and FU Orionis itself on January 26, 2011. We detect a number of previously unreported high-resolution K I and Ca II lines beyond 7500 <TEX>${\AA}$</TEX>. We resolve the H<TEX>${\alpha}$</TEX> and Ca II line profiles into three velocity components, which we attribute to both disk and outflow. The increased accretion during outburst can heat the disk to produce the relatively narrow absorption feature and launch outflows appearing as high velocity blue and red-shifted broad features.
292
- Tadross, A.L.
- Journal of the Korean astronomical society = 천문학회지
- 44, n.1
- pp.1-11
- 2011
- 원문 바로보기
A sample of 145 JHK-2MASS observations of NGC open star clusters is studied, of which 132 have never been studied before. Twelve are classified as non-open clusters and 13 are re-estimated self-consistently, after applying the same methods in order to compare and calibrate our reduction procedures. The fundamental and structural parameters of the 120 new open clusters studied here are derived using color-magnitude diagrams of JHK Near-IR photometry with the fitting of solar metallicity isochrones. We provide here, for the first time, a catalog of the main parameters for these 120 open clusters, namely, diameter, distance, reddening and age.
293
- 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.
294
- 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.
295
- 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.
296
- 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>.
297
- 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.
298
- 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.
299
- Andronov, Ivan L.
- Journal of the Korean astronomical society = 천문학회지
- 44, n.3
- pp.89-96
- 2011
- 원문 바로보기
We present results of two-color VR photometry of the intermediate polar RXS J1803. The data were aquired using the Korean 1-m telescope located at Mt. Lemmon, USA. Different 'high' and 'low' luminosity states, similar to other intermediate polars, were discovered. No statistically significant variability of the color index with varying luminosity was detected. The orbital variability was found to be not statistically significant. Spin maxima timings were determined, as well as the photometric ephemeris for the time interval of our observations. The spin period variations, caused by interaction of the accretion structure with the rotating magnetic white dwarf, were also detected. These variations are of complicated character, and their study requires further observations. We determine the color transformation coefficients for our photometric systems, and improve on the secondary photometric standards.
300
- Kang, Hye-Sung
- Journal of the Korean astronomical society = 천문학회지
- 44, n.2
- pp.49-58
- 2011
- 원문 바로보기
We calculate the energy spectra of cosmic ray (CR) protons and electrons at a plane shock with quasi-parallel magnetic fields, using time-dependent, diffusive shock acceleration (DSA) simulations, including energy losses via synchrotron emission and Inverse Compton (IC) scattering. A thermal leakage injection model and a Bohm type diffusion coefficient are adopted. The electron spectrum at the shock becomes steady after the DSA energy gains balance the synchrotron/IC losses, and it cuts off at the equilibrium momentum <TEX>$p_{eq}$</TEX>. In the postshock region the cutoff momentum of the electron spectrum decreases with the distance from the shock due to the energy losses and the thickness of the spatial distribution of electrons scales as <TEX>$p^{-1}$</TEX>. Thus the slope of the downstream integrated spectrum steepens by one power of p for <TEX>$p_{br}$</TEX> < p < <TEX>$p_{eq}$</TEX>, where the break momentum decreases with the shock age as <TEX>$p_{br}\;{\infty}\;t^{-1}$</TEX>. In a CR modified shock, both the proton and electron spectrum exhibit a concave curvature and deviate from the canonical test-particle power-law, and the upstream integrated electron spectrum could dominate over the downstream integrated spectrum near the cutoff momentum. Thus the spectral shape near the cutoff of X-ray synchrotron emission could reveal a signature of nonlinear DSA.