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한국천문학회지

1968년 ~ 2023년까지 1,187 건한국천문학회지를 격월간 확인하실 수 있습니다.

  • The Korean Astronomical Society (The Korean Astronomical Society)
  • 계간 (Quarterly)
  • ISSN : 1225-4614 (ISSN : 1225-4614)
  • DB구축현황 : 1,187건 (DB Construction : 1,187 Articles)
안내사항
총 게시글 1,187 페이지 2/119
11
  • Ki-Won Lee
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.1
  • pp.75-89
  • 2023
  • 원문 바로보기
We investigate the astronomical phenomenon records of Sukjong's Chunbang-Ilgi made by Sigangwon (Royal Educational Office of the Crown Prince) at which King Sukjong was the crown prince (i.e., 1667 January 24-1674 September 22). From the daily records of 2,799 days, we extract the astronomical records of 1,443 days and classify them into 14 categories. Then, we group the records of each category into five phenomena (Atmosphere, Eclipse, Daylight Appearance, Apparition, and Appulse) and compare them with the results of modern astronomical computations wherever possible. Except for Atmosphere group comprising records of meteorological events, such as solar halo, lunar halo, and unusual clouds, the significant findings in every other group are as follows: In Eclipse group, the solar eclipse that occurred on 1673 August 12 was unobservable in Korea, which is in contrast to the record of Joseonwangjo-Sillok (Annals of the Joseon Dynasty), which states that the sun was in eclipse around sunset time, as observed at Nam mountain. From the lunar eclipse records, we verify that the Joseon court did not change the date of the events observed after midnight. In Daylight Appearance group, we confirm that this phenomenon was observed during the daytime and not during twilight. We further suggest that if observation conditions are met, a celestial body brighter than -2.3 mag could be seen during the daytime with the naked-eye. In Apparition group, we find the possibilities that the Orionid meteor shower had influence on the meteor records and the seasonality on the aurora records. We also find that the Korean records in which the coma of comet C/1668 E1 was located below the horizon were overlooked in previous studies. Finally, we find that the records of Appulse group generally agree with the results of modern calculations. The records of Beom (trespass in literal) and Sik (eating in literal) events show average angular separations of 1.2° and 1.0°, respectively. In conclusion, we believe this work helps study the astronomical records of other logs of Sigangwon, such as Sukjong's Chunbang-Ilgi.
12
  • Jeong Ae Lee
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.2
  • pp.159-168
  • 2023
  • 원문 바로보기
The main goal of the Korean VLBI Network Calibrator Survey (KVNCS) is to expand the VLBI calibrators catalog for KVN, KaVA (KVN and VERA Array), EAVN (East-Asian VLBI Network), and other extended regions. The second KVNCS (KVNCS2) aimed to detect VLBI fringes of new candidates for calibrators in the K band. Out of the 1533 sources whose single-dish flux density in the K band was measured with KVN telescopes (Lee et al. 2017), 556 sources were observed with KVN in the K band. KVNCS2 confirmed the detection of VLBI fringes of 424 calibrator candidates over a single baseline. All detected sources had a high Signal-to-Noise Ratio (SNR) of >25. Finally, KVNCS2 confirmed 347 new candidates as VLBI calibrators in the K band, resulting in a 5% increase in the sky coverage compared to previous studies. The spatial distribution was quasi-uniform across the observable region (Dec. > -32.5°). In addition, the possibility as calibrator candidates for the detected sources was checked, using an analysis of the flux-flux relationship. Ultimately, the KVNCS catalog will not only become the VLBI calibrator list but is also useful as a database of compact radio sources for astronomical studies.
13
  • Jongil Jung
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.1
  • pp.117-124
  • 2023
  • 원문 바로보기
A Forbush decrease (FD) is a depression of cosmic ray (CR) intensity observed by ground-based neutron monitors (NMs). The CR intensity is thought to be modulated by the heliospheric magnetic structures including the interplanetary coronal mass ejection (ICME) surrounding the Earth. The different magnitude of the decreasing in intensity at each NM was explained only by the geomagnetic cutoff rigidity of the NM station. However, sometimes NMs of almost the same cutoff rigidity in northern and southern hemispheres observe the asymmetric intensity depression magnitudes of FD events. Thus, in this study we intend to see the effects on CR intensity modulation of FD event recorded at different NMs due to different ICME propagation directions as an additional parameter in the model explaining the CR modulation. Fortunately, since 2006 the coronagraphs of twin spacecraft of the STEREO mission allow us to infer the propagation direction of ICME associated with the FD event in 3-dimension with respect to the Earth. We suggest the hypothesis that the asymmetric CR modulations of FD events are determined by the propagation directions of the associated ICMEs.
14
  • Hyosun Kim
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.2
  • pp.149-157
  • 2023
  • 원문 바로보기
The propagation speed of a circumstellar pattern revealed in the plane of the sky is often assumed to represent the expansion speed of the wind matter ejected from a post-main-sequence star at the center. We point out that the often-adopted isotropic wind assumption and the binary hypothesis as the underlying origin for the circumstellar pattern in the shape of multilayered shells are, however, mutually incompatible. We revisit the hydrodynamic models for spiral-shell patterns induced by the orbital motion of a hypothesized binary, of which one star is losing mass at a high rate. The distributions of transverse wind velocities as a function of position angle in the plane of the sky are explored along viewing directions. The variation of the transverse wind velocity is as large as half the average wind velocity over the entire three dimensional domain in the simulated models investigated in this work. The directional dependence of the wind velocity is indicative of the overall morphology of the circumstellar material, implying that kinematic information is an important ingredient in modeling the snapshot monitoring (often in the optical and near-infrared) or the spectral imaging observations for molecular line emissions.
15
  • Bogyeong Kim
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.2
  • pp.187-194
  • 2023
  • 원문 바로보기
The remote sensing technique of measuring the magnetic field was applied first to sunspots by Hale (1908). Later Babcock (1961) showed that the solar surface magnetic field on a global scale is a dipole in first-order approximation and that this dipole field reverses once every solar cycle. The Wilcox Solar Observatory (WSO) supplies the spherical harmonics coefficients of the solar corona magnetic field of each Carrington Rotation, calculated based on the remotely-sensed photospheric magnetic field of the solar surface. To infer the internal current system producing the global solar coronal magnetic field structure and evolution of the Sun, we calculate the multipole components of the solar magnetic field using the WSO data from 1976 to 2019. The prominent cycle components over the last 4 solar activity cycles are axis-symmetric fields of the dipole and octupole. This implies that the current inversion driving the solar magnetic field reversal originates from the equatorial region and spreads to the whole globe. Thus, a more accurate solar dynamo model must include an explanation of the origin and evolution of such solar internal current dynamics.
16
  • Hye-Eun Jang
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.1
  • pp.11-22
  • 2023
  • 원문 바로보기
We report the result of a high-resolution spectroscopic study on seven magnesium (Mg) enhanced stars. The high Mg abundances in these stars imply that they were born in an environment heavily affected by the nucleosynthesis products of massive stars. We measure abundances of 16 elements including Mg and they show various abundance patterns implying their diverse origin. Three of our program stars show a very high Mg to Si ratio ([Mg/Si] &#x2248; 0.18-0.25), which might be well explained by fall-back supernovae or by supernovae with rapid rotating progenitors having an initial mass higher than about 20 M<sub>&#x2299;</sub>. Another three of our program stars have high light to heavy s-process element ratios ([Y/Ba] &#x2248; 0.30-0.44), which are consistent with the theoretical prediction of the nucleosynthesis in rapidly rotating massive stars with an initial mass of about M = 40 M<sub>&#x2299;</sub>. We also report a star having both high Y ([Y/Fe] = 0.2) and Ba ([Ba/Fe] = 0.28) abundance ratios, and it also shows the highest Zn abundance ratio ([Zn/Fe] = 0.27) among our sample, implying the nucleosynthesis by asymmetric supernova explosion induced by very rapid rotation of a massive progenitor having an initial mass between 20 M<sub>&#x2299;</sub> &#x2272; M &#x2272; 40 M<sub>&#x2299;</sub>. A relative deficiency of odd-number elements, which would be a signature of the pair-instability nucleosynthesis, is not found in our sample.
17
  • Minchul Kam
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.1
  • pp.1-9
  • 2023
  • 원문 바로보기
The Crab nebula is widely used as a polarization angle calibrator for single-dish radio observations because of its brightness, high degree of linear polarization, and well-known polarization angle over a wide frequency range. However, the Crab nebula cannot be directly used as a polarization angle calibrator for single-dish observations with the Korean VLBI Network (KVN), because the beam size of the telescopes is smaller than the size of the nebula. To determine the polarization angle of the Crab nebula as seen by KVN, we use 3C 286, a compact polarized extragalactic radio source whose polarization angle is well-known, as a reference target. We observed both the Crab nebula and 3C 286 with the KVN from 2017 to 2021 and find that the polarization angles at the total intensity peak of the Crab nebula (equatorial coordinates (J2000) R.A. = 05<sup>h</sup>34<sup>m</sup>32.3804<sup>s</sup> and Dec = 22&#x00B0;00'44.0982'') are 154.2&#x00B0; &#x00B1; 0.3&#x00B0;, 151.0&#x00B0; &#x00B1; 0.2&#x00B0;, 150.0&#x00B0; &#x00B1; 1.0&#x00B0;, and 151.3&#x00B0; &#x00B1; 1.1&#x00B0; at 22, 43, 86, and 94 GHz, respectively. We also find that the polarization angles at the pulsar position (RA = 05<sup>h</sup>34<sup>m</sup>31.971<sup>s</sup> and Dec = 22&#x00B0;00'52.06'') are 154.4&#x00B0; &#x00B1;0.4&#x00B0;, 150.7&#x00B0; &#x00B1;0.4&#x00B0;, and 149.0&#x00B0; &#x00B1; 1.0&#x00B0; for the KVN at 22, 43, and 86 GHz. At 129 GHz, we suggest to use the values 149.0&#x00B0; &#x00B1; 1.6&#x00B0; at the total intensity peak and 150.2&#x00B0; &#x00B1; 2.0&#x00B0; at the pulsar position obtained with the Institute for Radio Astronomy in the Millimeter Range (IRAM) 30-meter Telescope. Based on our study, both positions within the Crab nebula can be used as polarization angle calibrators for the KVN single-dish observations.
18
  • Jae Sok Oh
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.2
  • pp.169-185
  • 2023
  • 원문 바로보기
The GMT-Consortium Large Earth Finder (G-CLEF) is the first instrument for the Giant Magellan Telescope (GMT). G-CLEF is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. G-CLEF Flexure Control Camera (FCC) is included as a part in G-CLEF Front End Assembly (GCFEA), which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within GCFEA. FCC consists of an optical bench on which five optical components are installed. The order of the optical train is: a collimator, neutral density filters, a focus analyzer, a reimager and a detector (Andor iKon-L 936 CCD camera). The collimator consists of a triplet lens and receives the beam reflected by a fiber mirror. The neutral density filters make it possible a broad range star brightness as a target or a guide. The focus analyzer is used to measure a focus offset. The reimager focuses the beam from the collimator onto the CCD detector focal plane. The detector module includes a linear translator and a field de-rotator. We performed thermoelastic stress analysis for lenses and their mounts to confirm the physical safety of the lens materials. We also conducted the global structure analysis for various gravitational orientations to verify the image stability requirement during the operation of the telescope and the instrument. In this article, we present the opto-mechanical detailed design of G-CLEF FCC and describe the consequence of the numerical finite element analyses for the design.
19
  • Byeong-Cheol Lee
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.2
  • pp.277-286
  • 2023
  • 원문 바로보기
It is difficult to distinguish the pure signal produced by an orbiting planetary companion around giant stars from other possible sources, such as stellar spots, pulsations, or certain activities. Since 2003, we have obtained radial (RV) data from evolved stars using the high-resolution, fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at the Bohyunsan Optical Astronomy Observatory (BOAO). Here, we report the results of RV variations in the binary star HD 135438. We found two significant periods: 494.98 d with eccentricity of 0.23 and 8494.1 d with eccentricity of 0.83. Considering orbital stability, it is impossible to have two companions in such close orbits with high eccentricity. To determine the nature of the changes in the RV variability, we analyzed indicators of stellar spot and stellar chromospheric activity to find that there are no signals related to the significant period of 494.98 d. However, we calculated the upper limits of rotation period of the rotational velocity and found this to be 478-536 d. One possible interpretation is that this may be closely related to the rotational modulation of an orbital inclination at 67-90 degrees. The other signal corresponding to the period of 8494.1 d is probably associated with a stellar companion orbiting the giant star. A Markov Chain Monte Carlo (MCMC) simulation considering a single companion indicates that HD 135438 system hosts a stellar companion with 0.57<sup>+0.017</sup> <sub>-0.017</sub> M<sub>&#x2299;</sub> with an orbital period of 8498 d.
20
  • Byeong-Cheol Lee
  • Journal of the Korean astronomical society = 천문학회지
  • 56, n.1
  • pp.35-40
  • 2023
  • 원문 바로보기
We have been conducting a exoplanet search survey using Bohyunsan Observatory Echelle Spectrograph (BOES) for the last 18 years. We present the detection of exoplanet candidate in orbit around HD 18438 from high-precision radial velocity (RV) mesurements. The target was already reported in 2018 (Bang et al. 2018). They conclude that the RV variations with a period of 719 days are likely to be caused by the pulsations because the Lomb-Scargle periodogram of HIPPARCOS photometric and H<sub>&#x03B1;</sub> EW variations for HD 18438 show peaks with periods close to that of RV variations and there were no correlations between bisectors and RV measurements. However, the data were not sufficient to reach a firm conclusion. We obtained more RV data for four years. The longer time baseline yields a more accurate determination with a revised period of 803 &#x00B1; 5 days and the planetary origin of RV variations with a minimum planetary companion mass of 21 &#x00B1; 1 M<sub>Jup</sub>. Our current estimate of the stellar parameters for HD 18438 makes it currently the largest star with a planetary companion.