본문 바로가기 메뉴바로가기
통합검색

통합검색

한국천문학회지

1968년 ~ 2018년까지 1,081 건한국천문학회지를 격월간 확인하실 수 있습니다.

  • The Korean Astronomical Society (The Korean Astronomical Society)
  • 계간 (Quarterly)
  • ISSN : 1225-4614 (ISSN : 1225-4614)
  • DB구축현황 : 1,081건 (DB Construction : 1,081 Articles)
안내사항
총 게시글 1,081 페이지 5/109
41
  • 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 ( $M_V=-14.7{\pm}2.2mag$ ) and an amount of dust with visual extinction of ${\geq}2.8{\pm}2.2mag$ 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.
42
  • 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.
43
  • JEON, YISEUL
  • Journal of the Korean astronomical society = 천문학회지
  • 49, n.1
  • pp.25-35
  • 2016
  • 원문 바로보기
Multiple color selection techniques are successful in identifying quasars from wide-field broadband imaging survey data. Among the quasars that have been discovered so far, however, there is a redshift gap at 5 ? z ? 5.7 due to the limitations of filter sets in previous studies. In this work, we present a new selection technique of high redshift quasars using a sequence of medium-band filters: nine filters with central wavelengths from 625 to 1025 nm and bandwidths of 50 nm. Photometry with these medium-bands traces the spectral energy distribution (SED) of a source, similar to spectroscopy with resolution R ~ 15. By conducting medium-band observations of high redshift quasars at 4.7 ≤ z ≤ 6.0 and brown dwarfs (the main contaminants in high redshift quasar selection) using the SED camera for QUasars in EArly uNiverse (SQUEAN) on the 2.1-m telescope at the McDonald Observatory, we show that these medium-band filters are superior to multi-color broad-band color section in separating high redshift quasars from brown dwarfs. In addition, we show that redshifts of high redshift quasars can be determined to an accuracy of Δz/(1 + z) = 0.002 - 0.026. The selection technique can be extended to z ~ 7, suggesting that the medium-band observation can be powerful in identifying quasars even at the re-ionization epoch.
44
  • 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%.
45
  • KANG, HYESUNG
  • Journal of the Korean astronomical society = 천문학회지
  • 49, n.3
  • pp.83-92
  • 2016
  • 원문 바로보기
The Toothbrush radio relic associated with the merging cluster 1RXS J060303.3 is presumed to be produced by relativistic electrons accelerated at merger-driven shocks. Since the shock Mach number inferred from the observed radio spectral index, M radio ? 2.8, is larger than that estimated from X-ray observations, M X ? 1.5, we consider the re-acceleration model in which a weak shock of M s ? 1.2 - 1.5 sweeps through the intracluster plasma with a preshock population of relativistic electrons. We find the models with a power-law momentum spectrum with the slope, s ? 4.6, and the cutoff Lorentz factor, γ e,c ? 7-8×10 4 can reproduce reasonably well the observed profiles of radio uxes and integrated radio spectrum of the head portion of the Toothbrush relic. This study confirms the strong connection between the ubiquitous presence of fossil relativistic plasma originated from AGNs and the shock-acceleration model of radio relics in the intracluster medium.
46
  • TADROSS, A.L.
  • Journal of the Korean astronomical society = 천문학회지
  • 49, n.2
  • pp.53-57
  • 2016
  • 원문 바로보기
We present an optical UBVRI photometric analysis of the poorly studied open star cluster IC 2156 using Sloan Digital Sky Survey data in order to estimate its astrophysical properties. We compare these with results from our previous studies that relied on the 2MASS JHK near-infrared photometry. The stellar density distributions and color-magnitude diagrams of the cluster are used to determine its geometrical structure, real radius, core and tidal radii, and its distance from the Sun, the Galactic plane, and the Galactic center. We also estimate, the age, color excesses, reddening-free distance modulus, membership, total mass, luminosity function, mass function, and relaxation time of the cluster.
47
  • 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 radio ? 4.6, while the Mach number estimated from X-ray observations, M X?ray ? 2.7. In an attempt to resolve such a discrepancy, here we consider the re-acceleration model in which a shock of M s ? 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 e,c ? 3?5×10 4 , 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.
48
  • 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 confus ∼ 0.25′′, but future WFIRST (Wide Field Infrared Survey Telescope) observations will allow one to probe beyond this confusion limit as well.
49
  • HE, MATTHIAS YANG
  • Journal of the Korean astronomical society = 천문학회지
  • 49, n.5
  • pp.209-223
  • 2016
  • 원문 바로보기
We present analyses of ~1250 variable sources identified in a 20 square degree field toward NGC 2784 by the KMTNet Supernova Program. We categorize the variable sources into three groups based on their B-band variability. The first group consists of 31 high variability sources with their B-band RMS variability greater than 0.3 magnitudes. The second group of medium variability contains 265 sources with RMS variability between 0.05 and 0.3 magnitudes. The remaining 951 sources belong to the third group of low variability with an RMS variability smaller than 0.05 magnitudes. Of the entire ~1250 sources, 4 clearly show periods of variability greater than 100 days, while the rest have periods shorter than ~51 days or no reliable periods. The majority of the sources show either rather irregular variability or short periods faster than 2 days. Most of the sources with reliable period determination between 2 and 51 days belong to the low-variability group, although a few belong to the medium-variability group. All the variable sources with periods longer than 35 days appear to be very red with B - V > 1.5 and V - I > 2.1 magnitudes. We classify candidates of 51 Cepheids, 17 semi-regular variables, 3 Mira types, 2 RV(B) Tauri stars, 26 eclipsing binary systems and 1 active galactic nucleus. The majority of long-term variables in our sample belong to either Mira or semi-regular types, indicating that long-term variability may be more prominent in post-main sequence phases of late-type stars. The depth of the eclipsing dips of the 26 candidates for eclipsing binaries is equivalent to ~0.61 as the average relative size of the two stars in the binary system. Our results illustrate the power of the KMTNet Supernova Program for future studies of variable objects.
50
  • TRIPPE, SASCHA
  • Journal of the Korean astronomical society = 천문학회지
  • 49, n.5
  • pp.193-198
  • 2016
  • 원문 바로보기
Early-type galaxies (ETGs) are supposed to follow the virial relation $M=k_e{\sigma}^2R_e/G$ , with M being the mass, σ * being the stellar velocity dispersion, R e being the effective radius, G being Newton's constant, and k e being the virial factor, a geometry factor of order unity. Applying this relation to (a) the ATLAS 3D sample of Cappellari et al. (2013) and (b) the sample of Saglia et al. (2016) gives ensemble-averaged factors 〈k e 〉 = 5.15 ± 0.09 and 〈k e 〉 = 4.01 ± 0.18, respectively, with the difference arising from different definitions of effective velocity dispersions. The two datasets reveal a statistically significant tilt of the empirical relation relative to the theoretical virial relation such that $M{\propto}({\sigma}^2_*R_e)^{0.92}$ . This tilt disappears when replacing R e with the semi-major axis of the projected half-light ellipse, a. All best-fit scaling relations show zero intrinsic scatter, implying that the mass plane of ETGs is fully determined by the virial relation. Whenever a comparison is possible, my results are consistent with, and confirm, the results by Cappellari et al. (2013). The difference between the relations using either a or R e arises from a known lack of highly elliptical high-mass galaxies; this leads to a scaling (1 - ϵ ) ∝ M 0.12 , with ϵ being the ellipticity and $R_e=a\sqrt[]{1-{\epsilon}}$ . Accordingly, a, not R e , is the correct proxy for the scale radius of ETGs. By geometry, this implies that early-type galaxies are axisymmetric and oblate in general, in agreement with published results from modeling based on kinematics and light distributions.