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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 26/122
251
- 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.
252
- 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.
253
- 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.
254
- 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.
255
- Nwaffiah, J.U.
- Journal of the Korean astronomical society = 천문학회지
- 47, n.4
- pp.147-152
- 2014
- 원문 바로보기
We present measurements of the Fe <TEX>$K{\alpha}$</TEX> emission line of the intermediate polar V1223 Sagittarii observed with the Suzaku satellite. The spectrum is modeled with an absorbed thermal bremsstrahlung spectrum and three Gaussians for the three components of the Fe <TEX>$K{\alpha}$</TEX> lines. We resolve the neutral or low-ionized (6.41keV), He-like (6.70keV), and H-like (7.00keV) iron lines. We also obtain a thermal continuum temperature of 25 keV, which supports a thermal origin of the hard X-rays observed from the shock heated layers of gas between the white dwarf and the shock front. Hence, we believe that the He-like and H-like lines are from the collisional plasma. On the origin of the Fe <TEX>$K{\alpha}$</TEX> fluorescence line, we find that it could be partly from reflections of hard X-rays from the white dwarf surface and the <TEX>$N_H$</TEX> absorption columns. We also discuss the Fe <TEX>$K{\alpha}$</TEX> emission line as veritable tool for the probe of some astrophysical sites.
256
- Kim, Jae-Young
- Journal of the Korean astronomical society = 천문학회지
- 47, n.5
- pp.195-199
- 2014
- 원문 바로보기
We present a GUI-based interactive Python program, VIMAP, which generates radio spectral index maps of active galactic nuclei (AGN) from Very Long Baseline Interferometry (VLBI) maps obtained at different frequencies. VIMAP is a handy tool for the spectral analysis of synchrotron emission from AGN jets, specifically of spectral index distributions, turn-over frequencies, and core-shifts. In general, the required accurate image alignment is difficult to achieve because of a loss of absolute spatial coordinate information during VLBI data reduction (self-calibration) and/or intrinsic variations of source structure as function of frequency. These issues are overcome by VIMAP which in turn is based on the two-dimensional cross-correlation algorithm of Croke & Gabuzda (2008). In this paper, we briefly review the problem of aligning VLBI AGN maps, describe the workflow of VIMAP, and present an analysis of archival VLBI maps of the active nucleus 3C 120.
257
- Lee, Byeong-Cheol
- Journal of the Korean astronomical society = 천문학회지
- 47, n.2
- pp.69-76
- 2014
- 원문 바로보기
We report the detection of an exoplanet candidate in orbit around <TEX>${\sigma}$</TEX> Persei from a radial velocity (RV) survey. The system exhibits periodic RV variations of <TEX>$579.8{\pm}2.4$</TEX> days. The purpose of the survey is to search for low-amplitude and long-period RV variations in giants and examine the origin of the variations using the fiber-fed Bohyunsan Observatory Echelle Spectrograph installed at the 1.8-m telescope of Bohyunsan Optical Astronomy Observatory in Korea. We present high-accuracy RV measurements of <TEX>${\sigma}$</TEX> Per made from December 2003 to January 2014. We argue that the RV variations are not related to the surface inhomogeneities but instead a Keplerian motion of the planetary companion is the most likely explanation. Assuming a stellar mass of <TEX>$2.25{\pm}0.5$</TEX> <TEX>$M_{\odot}$</TEX>, we obtain a minimum planetary companion mass of <TEX>$6.5{\pm}1.0$</TEX> <TEX>$M_{Jup}$</TEX>, with an orbital semi-major axis of <TEX>$1.8{\pm}0.1$</TEX> AU, and an eccentricity of <TEX>$0.3{\pm}0.1$</TEX> around <TEX>${\sigma}$</TEX> Per.
258
- Kwon, Young-Joo
- Journal of the Korean astronomical society = 천문학회지
- 47, n.4
- pp.123-135
- 2014
- 원문 바로보기
A silicate carbon star is a carbon star which shows circumstellar silicate dust features. We collect a sample of 44 silicate carbon stars from the literature and investigate the validity of the classification. For some objects, it is uncertain whether the central star is a carbon star. We confirm that 29 objects are verified silicate carbon stars. We classify the confirmed objects into three subclasses based on the evolution phase of the central star. To investigate the effect of the chemical transition phase from O to C, we use the radiative transfer models for the detached silicate dust shells. The spectral energy distributions and the infrared two-color diagrams of the silicate carbon stars are compared with the theoretical model results. For the chemical transition model without considering the effect of a disk, we find that the life time of the silicate feature is about 50 to 400 years depending on the initial dust optical depth.
259
- Yang, Dan
- Journal of the Korean astronomical society = 천문학회지
- 47, n.3
- pp.105-113
- 2014
- 원문 바로보기
We apply differential affine velocity estimator (DAVE) to the Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) 12-min line-of-sight magnetograms, and separately calculate the injected magnetic helicity for the leading and the following polarities of nine emerging bipolar active regions (ARs). Comparing magnetic helicity flux of the leading polarity with the following polarity, we find that six ARs studied in this paper have the following polarity that injected more magnetic helicity flux than that of the leading polarity. We also measure the mean area of each polarity in all the nine ARs, and find that the compact polarity tend to possess more magnetic helicity flux than the fragmented one. Our results confirm the previous studies on asymmetry of magnetic helicity that emerging bipolar ARs have a polarity preference in injecting magnetic helicity. Based on the changes of unsigned magnetic flux, we divide the emergence process into two evolutionary stages: (1) an increasing stage before the peak flux and (2) a constant or decreasing stage after the peak flux. Obvious changes on magnetic helicity flux can be seen during transition from one stage to another. Seven ARs have one or both polarity that changed the sign of magnetic helicity flux. Additionally, the prevailing polarity of the two ARs, which injects more magnetic helicity, changes form the following polarity to the leading one.
260
- Yun, Youngjoo
- Journal of the Korean astronomical society = 천문학회지
- 47, n.6
- pp.201-207
- 2014
- 원문 바로보기
We report the development of solar flux receivers operating at 2.8 GHz to monitor solar radio activity. Radio waves from the sun are amplified, filtered, and then transmitted to a power meter sensor without frequency down-conversion. To measure solar flux, a calibration scheme is designed with a noise source, an ambient load, and a hot load at <TEX>$100^{\circ}C$</TEX>. The receiver is attached to a 1.8 m parabolic antenna in Icheon, owned by National Radio Research Agency, and observation is being conducted during day time on a daily basis. We compare the solar fluxes measured for last seven months with solar fluxes obtained by DRAO in Penticton, Canada, and by the Hiraiso solar observatory in Japan, and finally establish equations to convert observed flux to the so-called Penticton flux with an accuracy better than 3.2 sfu.