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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 27/123
261
OPTICAL MULTI-CHANNEL INTENSITY INTERFEROMETRY - OR: HOW TO RESOLVE O-STARS IN THE MAGELLANIC CLOUDS
- Trippe, Sascha
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.235-253
- 2014
- 원문 바로보기
Intensity interferometry, based on the Hanbury Brown-Twiss effect, is a simple and inexpensive method for optical interferometry at microarcsecond angular resolutions; its use in astronomy was abandoned in the 1970s because of low sensitivity. Motivated by recent technical developments, we argue that the sensitivity of large modern intensity interferometers can be improved by factors up to approximately 25 000, corresponding to 11 photometric magnitudes, compared to the pioneering Narrabri Stellar Interferometer. This is made possible by (i) using avalanche photodiodes (APD) as light detectors, (ii) distributing the light received from the source over multiple independent spectral channels, and (iii) use of arrays composed of multiple large light collectors. Our approach permits the construction of large (with baselines ranging from few kilometers to intercontinental distances) optical interferometers at the cost of (very) long-baseline radio interferometers. Realistic intensity interferometer designs are able to achieve limiting R-band magnitudes as good as <TEX>$m_R{\approx}14$</TEX>, sufficient for spatially resolved observations of main-sequence O-type stars in the Magellanic Clouds. Multi-channel intensity interferometers can address a wide variety of science cases: (i) linear radii, effective temperatures, and luminosities of stars, via direct measurements of stellar angular sizes; (ii) mass-radius relationships of compact stellar remnants, via direct measurements of the angular sizes of white dwarfs; (iii) stellar rotation, via observations of rotation flattening and surface gravity darkening; (iv) stellar convection and the interaction of stellar photospheres and magnetic fields, via observations of dark and bright starspots; (v) the structure and evolution of multiple stars, via mapping of the companion stars and of accretion flows in interacting binaries; (vi) direct measurements of interstellar distances, derived from angular diameters of stars or via the interferometric Baade-Wesselink method; (vii) the physics of gas accretion onto supermassive black holes, via resolved observations of the central engines of luminous active galactic nuclei; and (viii) calibration of amplitude interferometers by providing a sample of calibrator stars.
262
- Li, Xue-Bao
- Journal of the Korean astronomical society = 천문학회지
- 47, n.2
- pp.43-47
- 2014
- 원문 바로보기
Many advanced ground-based solar telescopes improve the spatial resolution of observation images using an adaptive optics (AO) system. As any AO correction remains only partial, it is necessary to use post-processing image reconstruction techniques such as speckle masking or shift-and-add (SAA) to reconstruct a high-spatial-resolution image from atmospherically degraded solar images. In the New Vacuum Solar Telescope (NVST), the spatial resolution in solar images is improved by frame selection and SAA. In order to overcome the burden of massive speckle data processing, we investigate the possibility of using the speckle reconstruction program in a real-time application at the telescope site. The code has been written in the C programming language and optimized for parallel processing in a multi-processor environment. We analyze the scalability of the code to identify possible bottlenecks, and we conclude that the presented code is capable of being run in real-time reconstruction applications at NVST and future large aperture solar telescopes if care is taken that the multi-processor environment has low latencies between the computation nodes.
263
- Minh, Young Chol
- Journal of the Korean astronomical society = 천문학회지
- 47, n.5
- pp.179-185
- 2014
- 원문 바로보기
We study the physical and chemical properties of the molecular clump hosting a young stellar cluster, IRAS 20160+3636, which is believed to have formed via the 'collect and collapse' process. Physical parameters of the UC H II region associated with the embedded cluster are measured from the radio continuum observations. This source is found to be a typical Galactic UC H II region, with a B0.5 type exciting star, if it is ionized by a single star. We derive a CN/HCN abundance ratio larger than 1 over this region, which may suggest that this clump is being affected by the UV radiation from the H II region.
264
- Gould, Andrew
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.279-291
- 2014
- 원문 바로보기
I show that the WFIRST microlensing survey will enable detection and precision orbit determination of Kuiper Belt Objects (KBOs) down to <TEX>$H_{vega}=28.2$</TEX> over an effective area of <TEX>${\sim}17deg^2$</TEX>. Typical fractional period errors will be <TEX>${\sim}1.5%{\times}10^{0.4(H-28.2)}$</TEX> with similar errors in other parameters for roughly 5000 KBOs. Binary companions to detected KBOs can be detected to even fainter limits, <TEX>$H_{vega}=29$</TEX>, corresponding to R~30.5 and effective diameters D~7 km. For KBOs H~23, binary companions can be found with separations down to 10 mas. This will provide an unprecedented probe of orbital resonance and KBO mass measurements. More than a thousand stellar occultations by KBOs can be combined to determine the mean size as a function of KBO magnitude down to H~25. Current ground-based microlensing surveys can make a significant start on finding and characterizing KBOs using existing and soon-to-be-acquired data.
265
- Cho, Il-Hyun
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.255-258
- 2014
- 원문 바로보기
Using sunspot number data from 270 historical stations for the period 1981-2013, we investigate their personal reduction coefficients (k) statistically. Chang & Oh (2012) perform a simulation showing that the k varies with the solar cycle. We try to verify their results using observational data. For this, a weighted mean and weighted standard deviation of monthly sunspot number are used to estimate the error from observed data. We find that the observed error (noise) is much smaller than that used in the simulation. Thus no distinct k-variation with the solar cycle is observed contrary to the simulation. In addition, the probability distribution of k is determined to be non-Gaussian with a fat-tail on the right side. This result implies that the relative sunspot number after 1981 might be overestimated since the mean value of k is less than that of the Gaussian distribution.
266
- Liu, Ying-Bo
- Journal of the Korean astronomical society = 천문학회지
- 47, n.3
- pp.115-122
- 2014
- 원문 바로보기
The New Vacuum Solar Telescope (NVST) is a 1-meter vacuum solar telescope that aims to observe the fine structures of active regions on the Sun. The main tasks of the NVST are high resolution imaging and spectral observations, including the measurements of the solar magnetic field. The NVST has been collecting more than 20 million FITS files since it began routine observations in 2012 and produces maximum observational records of 120 thousand files in a day. Given the large amount of files, the effective archiving and retrieval of files becomes a critical and urgent problem. In this study, we implement a new data archiving system for the NVST based on the Fastbit Not Only Structured Query Language (NoSQL) database. Comparing to the relational database (i.e., MySQL; My Structured Query Language), the Fastbit database manifests distinctive advantages on indexing and querying performance. In a large scale database of 40 million records, the multi-field combined query response time of Fastbit database is about 15 times faster and fully meets the requirements of the NVST. Our slestudy brings a new idea for massive astronomical data archiving and would contribute to the design of data management systems for other astronomical telescopes.
267
- Suh, Kyung-Won
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.219-233
- 2014
- 원문 바로보기
The main site of dust formation is believed to be the cool envelopes around AGB stars. Nearly all AGB stars can be identified as long-period variables (LPVs) with large amplitude pulsation. Shock waves produce by the strong pulsation and radiation pressure on newly formed dust grains drive dusty stellar winds with high mass-loss rates. IR observations of AGB stars identify various dust species in different physical conditions. Radio observations of gas phase materials are helpful to understand the overall properties of the stellar winds. In this paper, we review (i) classification of AGB stars; (ii) IR two-color diagrams of AGB stars; (iii) pulsation of AGB stars; (iv) dust around AGB stars including dusty stellar winds; (v) dust envelopes around AGB stars; (vi) mass-loss and evolution of AGB stars; and (vii) contribution of AGB dust to galactic environments. We discuss various observational evidences and their theoretical interpretations.
268
- Bong, Su-Chan
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.311-317
- 2014
- 원문 바로보기
Solar chromospheric surges are often reported to contain rotational motion. However, the details of the motion and driving mechanism of the surges are not yet fully understood. Recurrent surges with rotational motion at AR 10930 on the west limb are observed by Hinode Solar Optical Telescope (SOT) continuously from 11:21 UT on December 18 to 09:58 UT on December 19, 2006, using the <TEX>$Ca_{II}$</TEX> H broadband filter. We analyze details of the motion including number of turns from the rise of the surge to the fall, axial speed and acceleration. During the observation, rise and fall motion accompanying rotation appears recurrently. There occur a total of 14 surges at AR 10930 over 17 hours. The average duration is 45 minutes, and the average width, and length are 8 Mm, and 39 Mm, respectively. We speculate that the surges occurred by recurrent reconnections between the twisted prominence and large untwisted flux tube.
269
- Shin, Jihye
- Journal of the Korean astronomical society = 천문학회지
- 47, n.3
- pp.87-98
- 2014
- 원문 바로보기
We develop a parallel cosmological hydrodynamic simulation code designed for the study of formation and evolution of cosmological structures. The gravitational force is calculated using the TreePM method and the hydrodynamics is implemented based on the smoothed particle hydrodynamics. The initial displacement and velocity of simulation particles are calculated according to second-order Lagrangian perturbation theory using the power spectra of dark matter and baryonic matter. The initial background temperature is given by Recfast and the temperature uctuations at the initial particle position are assigned according to the adiabatic model. We use a time-limiter scheme over the individual time steps to capture shock-fronts and to ease the time-step tension between the shock and preshock particles. We also include the astrophysical gas processes of radiative heating/cooling, star formation, metal enrichment, and supernova feedback. We test the code in several standard cases such as one-dimensional Riemann problems, Kelvin-Helmholtz, and Sedov blast wave instability. Star formation on the galactic disk is investigated to check whether the Schmidt-Kennicutt relation is properly recovered. We also study global star formation history at different simulation resolutions and compare them with observations.
270
- Woo, Jong-Hak
- Journal of the Korean astronomical society = 천문학회지
- 47, n.5
- pp.167-178
- 2014
- 원문 바로보기
We search for misclassified type 1 AGNs among type 2 AGNs identified with emission line flux ratios, and investigate the properties of the sample. Using 4 113 local type 2 AGNs at 0.02 < z < 0.05 selected from Sloan Digital Sky Survey Data Release 7, we detected a broad component of the <TEX>$H{\alpha}$</TEX> line with a Full-Width at Half-Maximum (FWHM) ranging from 1 700 to <TEX>$19090km\;s^{-1}$</TEX> for 142 objects, based on the spectral decomposition and visual inspection. The fraction of the misclassified type 1 AGNs among type 2 AGN sample is ~3.5%, implying that a large number of missing type 1 AGN population may exist. The misclassified type 1 AGNs have relatively low luminosity with a mean broad <TEX>$H{\alpha}$</TEX> luminosity, log <TEX>$L_{H\alpha}=40.50{\pm}0.35\;erg\;s^{-1}$</TEX>, while black hole mass of the sample is comparable to that of the local black hole population, with a mean black hole mass, log <TEX>$M_{BH}=6.94{\pm}0.51\;M_{\odot}$</TEX>. The mean Eddington ratio of the sample is log <TEX>$L_{bol}/L_{Edd}=-2.00{\pm}0.40$</TEX>, indicating that black hole activity is relatively weak, hence, AGN continuum is too weak to change the host galaxy color. We find that the O III lines show significant velocity offsets, presumably due to outflows in the narrow-line region, while the velocity offset of the narrow component of the <TEX>$H{\alpha}$</TEX> line is not prominent, consistent with the ionized gas kinematics of general type 1 AGN population.