모달창 닫기
- 홈으로 이동
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 5/122
41
- Kwang-Il Seon
- Journal of the Korean astronomical society = 천문학회지
- 56, n.2
- pp.287-292
- 2023
- 원문 바로보기
This paper investigates the number of scatterings a photon undergoes in random walks before escaping from a medium. The number of scatterings in random walk processes is commonly approximated as τ + τ<sup>2</sup> in the literature, where τ is the optical thickness measured from the center of the medium. However, it is found that this formula is not accurate. In this study, analytical solutions in sphere and slab geometries are derived for both optically thin and optically thick limits, assuming isotropic scattering. These solutions are verified using Monte Carlo simulations. In the optically thick limit, the number of scatterings is found to be 0.5 τ<sup>2</sup> and 1.5 τ<sup>2</sup> in a sphere and slab, respectively. In the optically thin limit, the number of scatterings is ≈ τ in a sphere and ≈ τ (1 - γ - ln τ + τ) in a slab, where γ ≃ 0.57722 is the Euler-Mascheroni constant. Additionally, we present approximate formulas that reasonably reproduce the simulation results well in intermediate optical depths. These results are applicable to scattering processes that exhibit forward and backward symmetry, including both isotropic and Thomson scattering.
42
- Myoung-Seok Nam
- Journal of the Korean astronomical society = 천문학회지
- 56, n.2
- pp.231-252
- 2023
- 원문 바로보기
We present the analysis results of the simultaneous multifrequency observations of the blazar 4C +28.07. The observations were conducted by the Interferometric Monitoring of Gamma-ray Bright Active Galactic Nuclei (iMOGABA) program, which is a key science program of the Korean Very Long Baseline Interferometry (VLBI) Network (KVN). Observations of the iMOGABA program for 4C +28.07 were conducted from 16 January 2013 (MJD 56308) to 13 March 2020 (MJD 58921). We also used γ-ray data from the Fermi Large Array Telescope (Fermi-LAT) Light Curve Repository, covering the energy range from 100 MeV to 100 GeV. We divided the iMOGABA data and the Fermi-LAT data into five periods from 0 to 4, according to the prosody of the 22 GHz data and the presence or absence of the data. In order to investigate the characteristics of each period, the light curves were plotted and compared. However, a peak that formed a hill was observed earlier than the period of a strong γ-ray flare at 43-86 GHz in period 3 (MJD 57400-58100). Therefore, we assumed that the minimum total CLEANed flux density for each frequency was quiescent flux (S<sub>q</sub>) in which the core of 4C +28.07 emitted the minimum, with the variable flux (S<sub>var</sub>) obtained by subtracting S<sub>q</sub> from the values of the total CLEANed flux density. We then compared the variability of the spectral indices (α) between adjacent frequencies through a spectral analysis. Most notably, α<sub>22-43</sub> showed optically thick spectra in the absence of a strong γ-ray flare, and when the flare appeared, α<sub>22-43</sub> became optically thinner. In order to find out the characteristics of the magnetic field in the variable region, the magnetic field strength in the synchrotron self-absorption (B<sub>SSA</sub>) and the equipartition magnetic field strength (B<sub>eq</sub>) were obtained. We found that B<sub>SSA</sub> is largely consistent with B<sub>eq</sub> within the uncertainty, implying that the SSA region in the source is not significantly deviated from the equipartition condition in the γ-ray quiescent periods.
43
- Sang-Hyeon Ahn
- Journal of the Korean astronomical society = 천문학회지
- 56, n.2
- pp.201-212
- 2023
- 원문 바로보기
The inscription of Cheonsang Yeolcha Bunyajido (天象列次分野之圖) has the sun's locations at the equinoxes, which must have been copied from the astronomical treatises in Chinese historical annals, Songshu (宋書) and Jinshu (晉書). According to the treatises, an astronomer Wang Fan (王蕃, 228-266 CE) referred those values from a calendrical system called Qianxiangli (乾象曆, 223 CE), from which it is confirmed that it adopted the sun's location at the winter solstice of the <TEX>$(21{\frac{1}{4}})^{th}$</TEX> du of the 8th lunar lodge Dou (斗) as the reference direction for equatorial lodge angles. This indicates that the sun's locations at equinoxes and solstices in the calendrical system are the same as those in Jingchuli (景初曆, 237 CE). Hence, we propose that the sun's location at the autumnal equinox in Cheonsang Yeolcha Bunyajido should be corrected from 'wu du shao ruo' (五度少弱), meaning the <TEX>$(5{\frac{1}{6}})^{th}$</TEX> du, to 'wu du ruo' (五度弱), meaning the <TEX>$(4{\frac{11}{12}})^{th}$</TEX> du, of the first lunar lodge Jiao (角), as seen in Jingchuli. We reconstruct the polar coordinate system used in circular star charts, assuming that the mean motion rule was applied and its reference direction was the sun's location at the winter solstice. Considering the precession, we determined the observational epoch of the sun's location at the winter solstice to be t<sub>o</sub> = -18.3 ± 43.0 adopting the observational error of the so-called archaic determinatives (古度). It is noteworthy that the sun's locations at equinoxes inscribed in Cheonsang Yeolcha Bunyajido originated from Houhan Sifenli (後漢 四分曆) of the Latter Han dynasty (85 CE), while the coordinate origin in the star chart is related to Taichuli (太初曆) of the Former Han dynasty (104 BCE).
44
- Minsup Jeong
- Journal of the Korean astronomical society = 천문학회지
- 56, n.2
- pp.293-299
- 2023
- 원문 바로보기
The Wide-Angle Polarimetric Camera (PolCam) is installed on the Korea's lunar orbiter, Danuri, which launched on August 5, 2022. The mission objectives of PolCam are to construct photometric maps at a wavelength of 336 nm and polarization maps at 461 and 748 nm, with a phase angle range of 0°-135° and a spatial resolution of less than 100 m. PolCam is an imager using the push-broom method and has two cameras, Cam 1 and Cam 2, with a viewing angle of 45° to the right and left of the spacecraft's direction of orbit. We conducted performance tests in a laboratory setting before installing PolCam's flight model on the spacecraft. We analyzed the CCD's dark current, flat-field frame, spot size, and light flux. The dark current was obtained during thermal / vacuum test with various temperatures and the flat-field frame data was also obtained with an integrating sphere and tungsten light bulb. We describe the calibration method and results in this study.
45
- 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°00'44.0982'') are 154.2° ± 0.3°, 151.0° ± 0.2°, 150.0° ± 1.0°, and 151.3° ± 1.1° 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°00'52.06'') are 154.4° ±0.4°, 150.7° ±0.4°, and 149.0° ± 1.0° for the KVN at 22, 43, and 86 GHz. At 129 GHz, we suggest to use the values 149.0° ± 1.6° at the total intensity peak and 150.2° ± 2.0° 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.
46
- 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] ≈ 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>⊙</sub>. Another three of our program stars have high light to heavy s-process element ratios ([Y/Ba] ≈ 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>⊙</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>⊙</sub> ≲ M ≲ 40 M<sub>⊙</sub>. A relative deficiency of odd-number elements, which would be a signature of the pair-instability nucleosynthesis, is not found in our sample.
47
- 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.
48
- 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.
49
- Jiwoo Seo
- Journal of the Korean astronomical society = 천문학회지
- 56, n.1
- pp.41-57
- 2023
- 원문 바로보기
We measured temporal and emission properties of quiescent magnetars using archival Chandra and XMM-Newton data, produced a list of the properties for 17 magnetars, and revisited previously suggested correlations between the properties. Our studies carried out with a larger sample, better spectral characterizations, and more thorough analyses not only confirmed previously-suggested correlations but also found new ones. The observed correlations differ from those seen in other neutron-star populations but generally accord with magnetar models. Specifically, the trends of the intriguing correlations of blackbody luminosity (L<sub>BB</sub>) with the spin-inferred dipole magnetic field strength (B<sub>S</sub>) and characteristic age (τ<sub>c</sub>) were measured to be L<sub>BB</sub> ∝ B<sup>1.5</sup><sub>S</sub> and L<sub>BB</sub> ∝ τ<sup>-0.6</sup><sub>c</sub>, supporting the twisted magnetosphere and magnetothermal evolution models for magnetars. We report the analysis results and discuss our findings in the context of magnetar models.
50
- 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.