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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 15/123
141
- Seo, Hyunjong
- Journal of the Korean astronomical society = 천문학회지
- 51, n.3
- pp.49-63
- 2018
- 원문 바로보기
We carry out a study of Sub-Millimeter Galaxies (SMGs) in the AKARI NEP-Deep field using the James Clerk Maxwell Telescope (JCMT) SCUBA-2 <TEX>$850{\mu}m$</TEX> source catalog, released as part of the SCUBA-2 Cosmology Legacy Survey (S2CLS) program. The SCUBA-2 <TEX>$850{\mu}m$</TEX> map has a root mean square (rms) noise of <TEX>$1.2mJy\;beam^{-1}$</TEX> and covers an area of <TEX>$0.60degree^2$</TEX>. We find four SMGs which have counterparts to Herschel sources with spectroscopic redshifts in the literature. In addition, three dust obscured galaxies (DOGs) detected in Herschel bands are selected as a comparison sample. We derive IR luminosities of SMGs using the CIGALE code, which are similar to those of high redshift SMGs from previous studies. The contribution of AGN to the total IR luminosity in SMGs (2%-11%) is smaller than the lower limit for the one in DOGs (19%-35%), which is consistent with the expectation from the evolutionary scenario of massive galaxies. We search for SMGs in overdense regions as protocluster candidates and investigate four regions, including candidates around three DOGs. Finally, we argue that follow-up spectroscopic observation for the NEP-Deep field will provide crucial information to understand the role of SMGs in the evolution of massive galaxies.
142
- Hui, Chung-Yue
- Journal of the Korean astronomical society = 천문학회지
- 51, n.6
- pp.171-183
- 2018
- 원문 바로보기
To celebrate the tenth anniversary since the launch of Fermi Gamma-ray Space Telescope, we take a retrospect to a series of breakthroughs Fermi has contributed to pulsar astronomy in the last decade. Apart from significantly enlarging the population of <TEX>${\gamma}$</TEX>-ray pulsars, observations with the Large Area Telescope onboard Fermi also show the population is not homogeneous. Instead, many classes and sub-classes have been revealed. In this paper, we will review the properties of different types of <TEX>${\gamma}$</TEX>-ray pulsars, including radio-quiet <TEX>${\gamma}$</TEX>-ray pulsars, millisecond pulsars, <TEX>${\gamma}$</TEX>-ray binaries. Also, we will discuss the prospects of pulsar astronomy in the high energy regime.
143
- Yoo, Sung-Moon
- Journal of the Korean astronomical society = 천문학회지
- 51, n.5
- pp.143-153
- 2018
- 원문 바로보기
We present the first results of the invariant point (IVP) coordinates of the KVN Ulsan and Tamna radio telescopes. To determine the IVP coordinates in the geocentric frame (ITRF2014), a coordinate transformation method from the local frame, in which it is possible to survey using the optical instrument, to the geocentric frame was adopted. The least-square circles are fitted in three dimensions using the Gauss-Newton method to determine the azimuth and elevation axes in the local frame. The IVP in the local frame is defined as the mean value of the intersection points of the azimuth axis and the orthogonal vector between the azimuth and elevation axes. The geocentric coordinates of the IVP are determined by obtaining the seven transformation parameters between the local frame and the east-north-up (ENU) geodetic frame. The axis-offset between the azimuth and elevation axes is also estimated. To validate the results, the variation of coordinates of the GNSS station installed at KVN Ulsan was compared to the movement of the IVP coordinates over 9 months, showing good agreement in both magnitude and direction. This result will provide an important basis for geodetic and astrometric applications.
144
- Kang, Juhyung
- Journal of the Korean astronomical society = 천문학회지
- 51, n.6
- pp.207-214
- 2018
- 원문 바로보기
A coelostat is often used for solar observations, because it corrects the image rotation automatically by guiding sunlight into a fixed telescope with two plane mirrors. For the purposes of education and spectroscopic observation, the solar group at Seoul National University (SNU) plans to develop the SNU coelostat (SNUC) and install it in the SNU Astronomical Observatory (SAO). Requirements of the SNUC are < 1' positioning accuracy with 30 cm beam size on the entrance pupil in the compact dome. To allow for installation in the small dome, we design a compact slope type coelostat with a 45 cm primary plane mirror and a 39 cm secondary plane mirror. The motion of the SNUC is minimized by fixing the position of the slope frame. Numerical simulations of the available observational time of the designed coelostat shows that the sun can be observed ay all times from June to early August and at least three hours in other months. Since the high accuracy driving motors installed in the SNUC can be affected by external environment factors such as humidity and temperature variations, we design a prototype to test the significance of these effects. The prototype consists of a 20 cm primary plane mirror, a 1 m slope rail, a direct drive motor, a ballscrew, a linear motion guide, an AC servo motor, a reduction gear and a linear encoder. We plan to control and test the accuracy of the prototype with varying atmospheric conditions in early 2019. After testing the prototype, the SNUC will be manufactured and installed in SAO by 2020.
145
- Kang, Hyesung
- Journal of the Korean astronomical society = 천문학회지
- 51, n.6
- pp.185-195
- 2018
- 원문 바로보기
Galaxy clusters are known to host many active galaxies (AGNs) with radio jets, which could expand to form radio bubbles with relativistic electrons in the intracluster medium (ICM). It has been suggested that fossil relativistic electrons contained in remnant bubbles from extinct radio galaxies can be re-accelerated to radio-emitting energies by merger-driven shocks via diffusive shock acceleration (DSA), leading to the birth of radio relics detected in clusters. In this study we assume that such bubble consist primarily of thermal gas entrained from the surrounding medium and dynamically-insignificant amounts of relativistic electrons. We also consider several realistic models for magnetic fields in the cluster outskirts, including the ICM field that scales with the gas density as <TEX>$B_{ICM}{\infty}n^{0.5}_{ICM}$</TEX>. Then we perform time-dependent DSA simulations of a spherical shock that runs into a lower-density but higher-temperature bubble with the ratio <TEX>$n_b/n_{ICM}{\approx}T_{ICM}/T_b{\approx}0.5$</TEX>. We find that inside the bubble the shock speed increases by about 20 %, but the Mach number decreases by about 15% in the case under consideration. In this re-acceleration model, the observed properties of a radio relic such as radio flux, spectral index, and integrated spectrum would be governed mainly by the presence of seed relativistic electrons and the magnetic field profile as well as shock dynamics. Thus it is crucial to understand how fossil electrons are deposited by AGNs in the ICM and how the downstream magnetic field evolves behind the shock in detailed modeling of radio relics.
146
- Zheng, Yanfang
- Journal of the Korean astronomical society = 천문학회지
- 51, n.3
- pp.65-71
- 2018
- 원문 바로보기
The near real-time speckle masking reconstruction technique has been developed to accelerate the processing of solar images to achieve high resolutions for ground-based solar telescopes. However, the reconstruction of solar subimages in such a speckle reconstruction is very time-consuming. We design and implement a new parallel speckle masking reconstruction algorithm based on the Compute Unified Device Architecture (CUDA) on General Purpose Graphics Processing Units (GPGPU). Tests are performed to validate the correctness of our program on NVIDIA GPGPU. Details of several parallel reconstruction steps are presented, and the parallel implementation between various modules shows a significant speed increase compared to the previous serial implementations. In addition, we present a comparison of runtimes across serial programs, the OpenMP-based method, and the new parallel method. The new parallel method shows a clear advantage for large scale data processing, and a speedup of around 9 to 10 is achieved in reconstructing one solar subimage of <TEX>$256{\times}256pixels$</TEX>. The speedup performance of the new parallel method exceeds that of OpenMP-based method overall. We conclude that the new parallel method would be of value, and contribute to real-time reconstruction of an entire solar image.
147
- Li, Lin-Sen
- Journal of the Korean astronomical society = 천문학회지
- 51, n.1
- pp.1-4
- 2018
- 원문 바로보기
We study the pseudo-synchronous orbital motion of a binary system on the main sequence. The equations of the pseudo-synchronous orbit are derived up to <TEX>$O(e^4)$</TEX> where e is the eccentricy of the orbit. We integrate the equations to present their solutions. The theoretical results are applied to the evolution of the orbit and spin of the binary star Y Cygni, which has a current eccentricity of <TEX>$e_0\;=\;0.142$</TEX>. We tabulate our numerical results for the evolution of the orbit and spin per century. The numerical results for the semi-major axes and rotational angular velocities in the evolutional time scales of three stages (synchronization, circularization, and collapse time scale) are also tabulated. Synchronization is achieved in about <TEX>$5{\times}10^3\;years$</TEX> followed by circularization lasting about <TEX>$1{\times}10^5\;years$</TEX> before decaying in <TEX>$2{\times}10^5\;years$</TEX>.
148
- Ann, Hong Bae
- Journal of the Korean astronomical society = 천문학회지
- 51, n.4
- pp.73-88
- 2018
- 원문 바로보기
We present a sample of 54 disk galaxies which have well developed extraplanar structures. We selected them using visual inspections from the color images of the Sloan Digital Sky Survey. Since the sizes of the extraplanar structures are comparable to the disks, they are considered as prominent stellar halos rather than large bulges. A single <TEX>$S{\acute{e}}rsic$</TEX> profile fitted to the surface brightness along the minor-axis of the disk shows a luminosity excess in the central regions for the majority of sample galaxies. This central excess is considered to be caused by the central bulge component. The mean <TEX>$S{\acute{e}}rsic$</TEX> index of the single component model is <TEX>$1.1{\pm}0.9$</TEX>. A double <TEX>$S{\acute{e}}rsic$</TEX> profile model that employs n = 1 for the inner region, and varying n for the outer region, provides a better fit than the single <TEX>$S{\acute{e}}rsic$</TEX> profile model. For a small fraction of galaxies, a <TEX>$S{\acute{e}}rsic$</TEX> profile fitted with n = 4 for the inner region gives similar results. There is a weak tendency of increasing n with increasing luminosity and central velocity dispersion, but there is no dependence on the local background density.
149
- Suh, Kyung-Won
- Journal of the Korean astronomical society = 천문학회지
- 51, n.5
- pp.155-164
- 2018
- 원문 바로보기
We present various infrared two-color diagrams (2CDs) using WISE data for asymptotic giant branch (AGB) stars and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use the sample of 5036 AGB stars, 660 post-AGB stars, and 2748 PNe in our Galaxy. For each object, we cross-identify the IRAS, AKARI, WISE, and 2MASS counterparts. To investigate the spectral evolution from AGB stars to PNe, we compare the theoretical model tracks of AGB stars and post-AGB stars with the observations on the IR 2CDs. We find that the theoretical dust shell model tracks can roughly explain the observations of AGB stars, post-AGB stars, and PNe on the various IR 2CDs. WISE data are useful in studying the evolution of AGB stars and PNe, especially for dim objects. We find that most observed color indices generally increase during the evolution from AGB stars to PNe. We also find that <TEX>$Fe_{0.9}Mg_{0.1}O$</TEX> dust is useful to fit the observed WISE W3-W4 colors for O-rich AGB stars with thin dust shells.
150
- Seo, Jeongbhin
- Journal of the Korean astronomical society = 천문학회지
- 51, n.2
- pp.37-48
- 2018
- 원문 바로보기
Massive stars blow powerful stellar winds throughout their evolutionary stages from the main sequence to Wolf-Rayet phases. The amount of mechanical energy deposited in the interstellar medium by the wind from a massive star can be comparable to the explosion energy of a core-collapse supernova that detonates at the end of its life. In this study, we estimate the kinetic energy deposition by massive stars in our Galaxy by considering the integrated Galactic initial mass function and modeling the stellar wind luminosity. The mass loss rate and terminal velocity of stellar winds during the main sequence, red supergiant, and Wolf-Rayet stages are estimated by adopting theoretical calculations and observational data published in the literature. We find that the total stellar wind luminosity due to all massive stars in the Galaxy is about <TEX>${\mathcal{L}}_w{\approx}1.1{\times}10^{41}erg\;s^{-1}$</TEX>, which is about 1/4 of the power of supernova explosions, <TEX>${\mathcal{L}}_{SN}{\approx}4.8{\times}10^{41}erg\;s^{-1}$</TEX>. If we assume that ~ 1 - 10 % of the wind luminosity could be converted to Galactic cosmic rays (GCRs) through collisonless shocks such as termination shocks in stellar bubbles and superbubbles, colliding-wind shocks in binaries, and bow-shocks of massive runaway stars, stellar winds might be expected to make a significant contribution to GCR production, though lower than that of supernova remnants.