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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of The Korean Astronomical Society
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The Korean Astronomical Society
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Volume & Issues
Volume 49, Issue 4 - Aug 2016
Volume 49, Issue 3 - Jun 2016
Volume 49, Issue 2 - Apr 2016
Volume 49, Issue 1 - Feb 2016
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NON-GREY RADIATIVE TRANSFER IN THE PHOTOSPHERIC CONVECTION : VALIDITY OF THE EDDINGTON APPROXIMATION
BACH, KIEHUNN ;
Journal of The Korean Astronomical Society, volume 49, issue 1, 2016, Pages 1~8
DOI : 10.5303/JKAS.2016.49.1.1
The aim of this study is to describe the physical processes taking place in the solar photosphere. Based on 3D hydrodynamic simulations including a detailed radiation transfer scheme, we investigate thermodynamic structures and radiation fields in solar surface convection. As a starting model, the initial stratification in the outer envelope calculated using the solar calibrations in the context of the standard stellar theory. When the numerical fluid becomes thermally relaxed, the thermodynamic structure of the steady-state turbulent flow was explicitly collected. Particularly, a non-grey radiative transfer incorporating the opacity distribution function was considered in our calculations. In addition, we evaluate the classical approximations that are usually adopted in the onedimensional stellar structure models. We numerically reconfirm that radiation fields are well represented by the asymptotic characteristics of the Eddington approximation (the diffusion limit and the streaming limit). However, this classical approximation underestimates radiation energy in the shallow layers near the surface, which implies that a reliable treatment of the non-grey line opacities is crucial for the accurate description of the photospheric convection phenomenon.
Euclid ASTEROSEISMOLOGY AND KUIPER BELT OBJECTS
GOULD, ANDREW ; HUBER, DANIEL ; STELLO, DENNIS ;
Journal of The Korean Astronomical Society, volume 49, issue 1, 2016, Pages 9~18
DOI : 10.5303/JKAS.2016.49.1.9
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%.
STRUCTURE OF A MAGNETIC DECREASE OBSERVED IN A COROTATING INTERACTION REGION
LEE, ENSANG ; PARKS, GEORGE K. ;
Journal of The Korean Astronomical Society, volume 49, issue 1, 2016, Pages 19~23
DOI : 10.5303/JKAS.2016.49.1.19
Magnetic decreases are often observed in various regions of interplanetary space. Many studies are devoted to reveal the physical nature and generation mechanism of the magnetic decreases, but still we do not fully understand magnetic decreases. In this study, we investigate the structure of a magnetic decrease observed in a corotating interaction region using multi-spacecraft measurements. We use three spacecraft, ACE, Cluster, and Wind, which were widely separated in the x- and y-directions in the geocentric solar ecliptic (GSE) coordinates. The boundaries of the magnetic decrease are the same at the three locations and can be identified as tangential discontinuities. A notable feature is that the magnetic decrease has very large dimension, ≳ R
, along the boundary, which is much larger than the size, ~ 6 R
, along the normal direction. This suggests that the magnetic decrease has a shape of a long, thin rod or a wide slab.
THE INFRARED MEDIUM-DEEP SURVEY. V. A NEW SELECTION STRATEGY FOR QUASARS AT z > 5 BASED ON MEDIUM-BAND OBSERVATIONS WITH SQUEAN
JEON, YISEUL ; IM, MYUNGSHIN ; PAK, SOOJONG ; HYUN, MINHEE ; KIM, SANGHYUK ; KIM, YONGJUNG ; LEE, HYE-IN ; PARK, WOOJIN ;
Journal of The Korean Astronomical Society, volume 49, issue 1, 2016, Pages 25~35
DOI : 10.5303/JKAS.2016.49.1.25
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.
KMTNET: A NETWORK OF 1.6 M WIDE-FIELD OPTICAL TELESCOPES INSTALLED AT THREE SOUTHERN OBSERVATORIES
KIM, SEUNG-LEE ; LEE, CHUNG-UK ; PARK, BYEONG-GON ; KIM, DONG-JIN ; CHA, SANG-MOK ; LEE, YONGSEOK ; HAN, CHEONGHO ; CHUN, MOO-YOUNG ; YUK, INSOO ;
Journal of The Korean Astronomical Society, volume 49, issue 1, 2016, Pages 37~44
DOI : 10.5303/JKAS.2016.49.1.37
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.
A NEW METHOD TO DETERMINE THE TEMPERATURE OF CMES USING A CORONAGRAPH FILTER SYSTEM
CHO, KYUHYOUN ; CHAE, JONGCHUL ; LIM, EUN-KYUNG ; CHO, KYUNG-SUK ; BONG, SU-CHAN ; YANG, HEESU ;
Journal of The Korean Astronomical Society, volume 49, issue 1, 2016, Pages 45~51
DOI : 10.5303/JKAS.2016.49.1.45
The coronagraph is an instrument that enables the investigation of faint features in the vicinity of the Sun, particularly coronal mass ejections (CMEs). So far coronagraphic observations have been mainly used to determine the geometric and kinematic parameters of CMEs. Here, we introduce a new method for the determination of CME temperature using a two filter (4025 Å and 3934 Å) coronagraph system. The thermal motion of free electrons in CMEs broadens the absorption lines in the optical spectra that are produced by the Thomson scattering of visible light originating in the photosphere, which affects the intensity ratio at two different wavelengths. Thus the CME temperature can be inferred from the intensity ratio measured by the two filter coronagraph system. We demonstrate the method by invoking the graduated cylindrical shell (GCS) model for the 3-dimensional CME density distribution and discuss its significance.