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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 32/122
311
- 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.
312
- 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>.
313
- 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.
314
- 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.
315
- Deng, Lin-Hua
- Journal of the Korean astronomical society = 천문학회지
- 44, n.6
- pp.209-215
- 2011
- 원문 바로보기
In this paper, the long-term hemispheric variation of the polar faculae is investigated. It is found that, (1) both the N-S asymmetry and N-S asynchrony of the polar faculae exhibit a long-term persistence, which suggests that they should not be regarded as a stochastic phenomenon; (2) both the N-S asynchrony and N-S asymmetry of the polar faculae are functions of the latitude, implying that the N-S asynchrony of the polar faculae is related to the N-S asymmetry of the polar faculae; (3) from a long-term view, the dominant hemisphere of the polar faculae seems to have close connection with the phase-leading hemisphere of the polar faculae.
316
- Kim, Ju-Han
- Journal of the Korean astronomical society = 천문학회지
- 44, n.6
- pp.217-234
- 2011
- 원문 바로보기
We present two large cosmological N-body simulations, called Horizon Run 2 (HR2) and Horizon Run 3 (HR3), made using <TEX>$6000^3$</TEX> = 216 billions and <TEX>$7210^3$</TEX> = 374 billion particles, spanning a volume of <TEX>$(7.200\;h^{-1}Gpc)^3$</TEX> and <TEX>$(10.815\;h^{-1}Gpc)^3$</TEX>, respectively. These simulations improve on our previous Horizon Run 1 (HR1) up to a factor of 4.4 in volume, and range from 2600 to over 8800 times the volume of the Millennium Run. In addition, they achieve a considerably finer mass resolution, down to <TEX>$1.25{\times}10^{11}h^{-1}M_{\odot}$</TEX>, allowing to resolve galaxy-size halos with mean particle separations of <TEX>$1.2h^{-1}$</TEX>Mpc and <TEX>$1.5h^{-1}$</TEX>Mpc, respectively. We have measured the power spectrum, correlation function, mass function and basic halo properties with percent level accuracy, and verified that they correctly reproduce the CDM theoretical expectations, in excellent agreement with linear perturbation theory. Our unprecedentedly large-volume N-body simulations can be used for a variety of studies in cosmology and astrophysics, ranging from large-scale structure topology, baryon acoustic oscillations, dark energy and the characterization of the expansion history of the Universe, till galaxy formation science - in connection with the new SDSS-III. To this end, we made a total of 35 all-sky mock surveys along the past light cone out to z = 0.7 (8 from the HR2 and 27 from the HR3), to simulate the BOSS geometry. The simulations and mock surveys are already publicly available at http://astro.kias.re.kr/Horizon-Run23/.
317
- Le, Huynh Anh Nguyena
- Journal of the Korean astronomical society = 천문학회지
- 44, n.4
- pp.125-134
- 2011
- 원문 바로보기
We present medium resolution (R = 5000 - 6000) spectra in the near-infrared band, 1.4 - 1.8 <TEX>${\mu}m$</TEX>, for template stars in G, K, and M types observed by the echelle spectrometer, IRCS, at the SUBARU 8.2 m telescope. The identification of lines is based on the spectra of Arcturus (K2 III) in the literature. We measured the equivalent of widths and compared our results to those of Meyer et al. (1998). We conclude that our spectral resolution (R = 6000) data can investigate more accurately the properties of lines in stellar spectra. The library of the template stellar spectra in ASCII format are available for download on the World Wide Web.
318
- 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.
319
- 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.
320
- Kim, Jae-Yeong
- Journal of the Korean astronomical society = 천문학회지
- 44, n.4
- pp.135-142
- 2011
- 원문 바로보기
A <TEX>$200'{\times}200'$</TEX> region around 30 Doradus in the Large Magellanic Cloud (LMC) is observed and analyzed in the near-infrared. We obtain polarimetry data in the J, H, and Ks bands using the SIRIUS polarimeter SIRPOL at the Infrared Survey Facility 1.4 m telescope. We measure the Stokes parameters of 2562 point-like sources to derive the degree of polarization and the polarization position angles. We discuss the statistics of the groups classified by color-magnitude diagram and proper motions of the sources, in order to separate the Galactic foreground sources from those present in the LMC. We notice that groups classified by the proper motion data show a tendency towards different polarimetric properties.