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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 19/122
181
- Lee, Yongung
- Journal of the Korean astronomical society = 천문학회지
- 49, n.6
- pp.255-259
- 2016
- 원문 바로보기
We estimate the fractal dimension of the <TEX>${\rho}$</TEX> Ophiuchus Molecular Cloud Complex, associated with star forming regions. We selected a cube (<TEX>${\upsilon}$</TEX>, l, b) database, obtained with J = 1-0 transition lines of <TEX>$^{12}CO$</TEX> and <TEX>$^{13}CO$</TEX> at a resolution of 22' using a multibeam receiver system on the 14-m telescope of the Five College Radio Astronomy Observatory. Using a code developed within IRAF, we identified slice-clouds with two threshold temperatures to estimate the fractal dimension. With threshold temperatures of 2.25 K (<TEX>$3{\sigma}$</TEX>) and 3.75 K (<TEX>$5{\sigma}$</TEX>), the fractal dimension of the target cloud is estimated to be D = 1.52-1.54, where <TEX>$P{\propto}A^{D/2}$</TEX>, which is larger than previous results. We suggest that the sampling rate (spatial resolution) of observed data must be an important parameter when estimating the fractal dimension, and that narrower or wider dispersion around an arbitrary fit line and the intercepts at NP = 100 should be checked whether they relate to firms noise level or characteristic structure of the target cloud. This issue could be investigated by analysing several high resolution databases with different quality (low or moderate sensitivity).
182
- SUH, KYUNG-WON
- Journal of the Korean astronomical society = 천문학회지
- 49, n.4
- pp.127-136
- 2016
- 원문 바로보기
We investigate optical properties of amorphous alumina (Al2O3) dust grains in the envelopes around O-rich asymptotic giant branch (AGB) stars using laboratory measured optical data. We derive the optical constants of amorphous alumina over a wide wavelength range that satisfy the Kramers-Kronig relation and reproduce the laboratory data. Using the amorphous alumina and silicate dust, we compare the radiative transfer model results with the observed spectral energy distributions. Comparing the theoretical models with observations on various IR two-color diagrams for a large sample of O-rich AGB stars, we find that the amorphous alumina dust (about 10-40%) mixed with amorphous silicate better models the observed points for the O-rich AGB stars with thin dust envelopes.
183
- LEE, ENSANG
- Journal of the Korean astronomical society = 천문학회지
- 49, n.2
- pp.59-64
- 2016
- 원문 바로보기
In this study, we investigate the kinetic properties of magnetic decreases observed in the solar wind at ~1 AU using the Cluster observations. We study two different magnetic decreases: one with a short observation duration of ~2.5 minutes and stable structure and the other with a longer observation duration of ~40 minutes and some fluctuations and substructures. Despite the contrast in durations and magnetic structures, the velocity space distributions of ions are similar in both events. The velocity space distribution becomes more anisotropic along the direction parallel to the magnetic field, which differs from observations obtained at high heliographic latitudes. On the other hand, electrons show different features from the ions. The core component of the electrons shows similar anisotropy to the ions, though the anisotropy is much weaker. However, while ions are heated in the magnetic decreases, the core electrons are slightly cooled, especially in the perpendicular direction. The halo component does not change much in the magnetic decreases from the ambient solar wind. The strahl component is observed only in one of the magnetic decreases. The results imply that the ions and electrons in the magnetic decreases can behave differently, which should be considered for the formation mechanism of the magnetic decreases.
184
- Park, Changbom
- Journal of the Korean astronomical society = 천문학회지
- 49, n.6
- pp.233-238
- 2016
- 원문 바로보기
The missing historical record of the Cassiopeia A (Cas A) supernova (SN) event implies a large extinction to the SN, possibly greater than the interstellar extinction to the current SN remnant. Here we investigate the possibility that the guest star that appeared near Cas A in 1592-1593 in Korean history books could have been an 'impostor' of the Cas A SN, i.e., a luminous transient that appeared to be a SN but did not destroy the progenitor star, with strong mass loss to have provided extra circumstellar extinction. We first review the Korean records and show that a spatial coincidence between the guest star and Cas A cannot be ruled out, as opposed to previous studies. Based on modern astrophysical findings on core-collapse SN, we argue that Cas A could have had an impostor and derive its anticipated properties. It turned out that the Cas A SN impostor must have been bright (<TEX>$M_V=-14.7{\pm}2.2mag$</TEX>) and an amount of dust with visual extinction of <TEX>${\geq}2.8{\pm}2.2mag$</TEX> should have formed in the ejected envelope and/or in a strong wind afterwards. The mass loss needs to have been spherically asymmetric in order to see the light echo from the SN event but not the one from the impostor event.
185
- KIM, SEUNG-LEE
- Journal of the Korean astronomical society = 천문학회지
- 49, n.1
- pp.37-44
- 2016
- 원문 바로보기
The Korea Microlensing Telescope Network (KMTNet) is a wide-field photometric system installed by the Korea Astronomy and Space Science Institute (KASI). Here, we present the overall technical specifications of the KMTNet observation system, test observation results, data transfer and image processing procedure, and finally, the KMTNet science programs. The system consists of three 1.6 m wide-field optical telescopes equipped with mosaic CCD cameras of 18k by 18k pixels. Each telescope provides a 2.0 by 2.0 square degree field of view. We have finished installing all three telescopes and cameras sequentially at the Cerro-Tololo Inter-American Observatory (CTIO) in Chile, the South African Astronomical Observatory (SAAO) in South Africa, and the Siding Spring Observatory (SSO) in Australia. This network of telescopes, which is spread over three different continents at a similar latitude of about -30 degrees, enables 24-hour continuous monitoring of targets observable in the Southern Hemisphere. The test observations showed good image quality that meets the seeing requirement of less than 1.0 arcsec in I-band. All of the observation data are transferred to the KMTNet data center at KASI via the international network communication and are processed with the KMTNet data pipeline. The primary scientific goal of the KMTNet is to discover numerous extrasolar planets toward the Galactic bulge by using the gravitational microlensing technique, especially earth-mass planets in the habitable zone. During the non-bulge season, the system is used for wide-field photometric survey science on supernovae, asteroids, and external galaxies.
186
- GOULD, ANDREW
- Journal of the Korean astronomical society = 천문학회지
- 49, n.1
- pp.9-18
- 2016
- 원문 바로보기
Euclid, which is primarily a dark-energy/cosmology mission, may have a microlensing component, consisting of perhaps four dedicated one-month campaigns aimed at the Galactic bulge. We show that such a program would yield excellent auxilliary science, including asteroseismology detections for about 100 000 giant stars, and detection of about 1000 Kuiper Belt Objects (KBOs), down to 2-2.5 mag below the observed break in the KBO luminosity function at I ∼ 26. For the 400 KBOs below the break, Euclid will measure accurate orbits, with fractional period errors ≲ 2.5%.
187
- GOULD, ANDREW
- Journal of the Korean astronomical society = 천문학회지
- 49, n.4
- pp.123-126
- 2016
- 원문 바로보기
Microlensing is generally thought to probe planetary systems only out to a few Einstein radii. Microlensing events generated by bound planets beyond about 10 Einstein radii generally do not yield any trace of their hosts, and so would be classified as free floating planets (FFPs). I show that it is already possible, using adaptive optics (AO), to constrain the presence of potential hosts to FFP candidates at separations comparable to the Oort Cloud. With next-generation telescopes, planets at Kuiper-Belt separations can be probed. Next generation telescopes will also permit routine vetting for all FFP candidates, simply by obtaining second epochs 4-8 years after the event. At present, the search for such hosts is restricted to within the 'confusion limit' of θ<sub>confus</sub> ∼ 0.25′′, but future WFIRST (Wide Field Infrared Survey Telescope) observations will allow one to probe beyond this confusion limit as well.
188
- KANG, HYESUNG
- Journal of the Korean astronomical society = 천문학회지
- 49, n.4
- pp.145-155
- 2016
- 원문 바로보기
The Sausage radio relic is the arc-like radio structure in the cluster CIZA J2242.8+5301, whose observed properties can be best understood by synchrotron emission from relativistic electrons accelerated at a merger-driven shock. However, there remain a few puzzles that cannot be explained by the shock acceleration model with only in-situ injection. In particular, the Mach number inferred from the observed radio spectral index, M<sub>radio</sub> ≈ 4.6, while the Mach number estimated from X-ray observations, M<sub>X−ray</sub> ≈ 2.7. In an attempt to resolve such a discrepancy, here we consider the re-acceleration model in which a shock of M<sub>s</sub> ≈ 3 sweeps through the intracluster gas with a pre-existing population of relativistic electrons. We find that observed brightness profiles at multi frequencies provide strong constraints on the spectral shape of pre-existing electrons. The models with a power-law momentum spectrum with the slope, s ≈ 4.1, and the cutoff Lorentz factor, γ<sub>e,c</sub> ≈ 3−5×10<sup>4</sup>, can reproduce reasonably well the observed spatial profiles of radio fluxes and integrated radio spectrum of the Sausage relic. The possible origins of such relativistic electrons in the intracluster medium remain to be investigated further.
189
- LEE, KI-WON
- Journal of the Korean astronomical society = 천문학회지
- 49, n.4
- pp.163-173
- 2016
- 원문 바로보기
In this paper, we study the lunar eclipse records in the Goryeosa (History of the Goryeo Dynasty), an official history book of the Goryeo dynasty (A.D. 918 - 1392). In the history book, a total of 228 lunar eclipse accounts are recorded, covering the period from 1009 to 1392. However, we find that two accounts are duplications and four accounts correspond to no known lunar eclipses around the dates. For the remaining lunar eclipses, we calculate the magnitude and the time of the eclipse at different phases using the DE406 ephemeris. Of the 222 lunar eclipse accounts, we find that the minimum penumbral magnitude was 0.5583. For eclipses which occurred after midnight, we find that some accounts were recorded on the day before the eclipse, like the astronomical records of the Joseonwangjosillok (Annals of the Joseon Dynasty), while others were on the day of the lunar eclipse. We also find that four accounts show a difference in the Julian dates between this study and that of Ahn et al., even though it is assumed that the Goryeo court did not change the dates in the accounts for lunar eclipses that occurred after midnight. With regard to the contents of the lunar eclipse accounts, we confirm that the accounts recorded as total eclipses are accurate, except for two accounts. However, both eclipses were very close to the total eclipse. We also confirm that all predicted lunar eclipses did occur, although one eclipse happened two days after the predicted date. In conclusion, we believe that this study is very helpful for investigating the lunar eclipse accounts of other periods in Korea, and furthermore, useful for verifying the calendar dates of the Goryeo dynasty.
190
- JEONG, WOONG-SEOB
- Journal of the Korean astronomical society = 천문학회지
- 49, n.5
- pp.225-232
- 2016
- 원문 바로보기
We present an optical imaging survey of AKARI Deep Field South (ADF-S) using the Korea Microlensing Telescope Network (KMTNet), to find optical counterparts of dusty star-forming galaxies. The ADF-S is a deep far-infrared imaging survey region with AKARI covering around 12 deg<sup>2</sup>, where the deep optical imaging data are not yet available. By utilizing the wide-field capability of the KMTNet telescopes (~4 deg<sup>2</sup>), we obtain optical images in B, R and I bands for three regions. The target depth of images in B, R and I bands is ~24 mag (AB) at 5σ, which enables us to detect most dusty star-forming galaxies discovered by AKARI in the ADF-S. Those optical datasets will be helpful to constrain optical spectral energy distributions as well as to identify rare types of dusty star-forming galaxies such as dust-obscured galaxy, sub-millimeter galaxy at high redshift.