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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 2/122
11
- Jeongwhan Han
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.25-33
- 2024
- 원문 바로보기
In order to attract students to the radio universe, we have constructed a three-element radio interferometer in the National Youth Space Center, Goheung, Korea. It consists of three 1.8 m off-axis parabola antennas with driving systems, sideband separation receivers operating in 12 GHz, a narrow band digitizer, and correlation software. We have used as many commercial products as possible to reduce development costs. The maximum separation of 20 m gives an angular resolution of ~4', and the shortest baseline of 3.8 m prevents a serious missing flux. Fringes are detected for several radio sources, including the sun and Cas A. After a rough relative calibration, we have derived visibilities for the sun, whose amplitudes are decreasing for longer baselines. We have made a solar image using the visibility amplitudes and closure phases, referring to the 17 GHz image by Nobeyama Radioheliograph. Developing a flexible real-time correlator seems most crucial if this kind of the system is to be used for more rigorous scientific studies.
12
- Eunjin Cho
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.83-94
- 2024
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The Jupiter Trojans are believed to have originated from the primordial trans-Neptunian disk, which also gave rise to the dynamically hot Kuiper Belt Objects (KBOs). Unlike the Centaurs, which were derived from the KBOs and exhibit comet-like activities, the current Trojans do not display any such behavior. However, due to their orbital history, it is possible that the Trojans experienced Centaur-like behaviors just after being captured. This paper employs numerical simulations to investigate whether the Trojans had comet-like activities in the early stage. The model results show that if the Trojans contained initially amorphous water ice, sporadic outbursts of gas and dust would have occurred at the surface, resulting in the ejection of unirradiated, less-red dust grains from near the crystallization front. These grains may have covered the surface and altered the surface colors, indicating that the crystallization process may have changed the colors of some Trojans, including the very-red ones, to a more neutral color during the early stages after they came into the current Trojan location. Our results suggest the potential influence of internal dust ejections by ancient outbursts of some Trojans on their color distribution.
13
- Sibaek Yi
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.13-24
- 2024
- 원문 바로보기
A force-free field (FFF) is determined solely by the normal components of magnetic field and current density on the entire boundary of the domain. Methods employing three components of magnetic field suffer from overspecification of boundary conditions and/or a nonzero divergence-B problem. A vector potential formulation eliminates the latter issue, but introduces difficulties in imposing the normal component of current density at the boundary. This paper proposes four different boundary treatment methods within the vector potential formulation. We conduct a comparative analysis of the vector potential FFF solvers that we have developed incorporating these methods against other FFF codes in different magnetic field representations. Although the vector potential solvers with the new boundary treatments do not outperform our poloidal-toroidal formulation code, they demonstrate comparable or superior performance compared to the optimization code in SolarSoftWare. The methods developed here are expected to be readily applied not only to force-free field computations but also to time-dependent data-driven simulations.
14
- Yun-A Jo
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.135-143
- 2024
- 원문 바로보기
Much effort has been carried out to calibrate and revise asteroseismic relations, given their importance of relations in asteroseismology in determining fundamental parameters of stars. In this study, we statistically explore asteroseismic relations with partial correlation coefficients to determine the most fundamental parameters, separately analyzing asteroseismic data based on the evolutionary status of stars from main sequence up to core helium-burning red-clump stars. We have found that regardless of the evolutionary status of the sampled stars the surface gravity and density of stars strongly influence the observed correlations. More importantly, it is found that indirect correlations derived considering the influence of confounding parameters are subject to the evolutionary status. For example, the observed correlation of the large frequency separation ∆𝜈 with the central frequency 𝜈<sub>max</sub> is influenced by the stellar mass, radius, and luminosity only for main sequence stars. The observed correlation of the width of the Gaussian envelope 𝛿𝜈<sub>env</sub> with 𝜈<sub>max</sub> is influenced by the stellar mass, effective temperature, radius, and luminosity for main-sequence and subgiant stars. The observed relation between ∆𝜈 and the small frequency separation 𝛿𝜈<sub>02</sub> is influenced by the stellar mass, radius, and luminosity for main-sequence and subgiant stars. In contrast, effective temperature, metallicity, and age do not seem to significantly affect the observed correlations. Finally, we conclude by discussing implication of our findings.
15
- Shan Li
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.67-82
- 2024
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In this study, we conduct a multi-frequency analysis of the gamma-ray bright blazar 1308+326 from February 2013 to March 2020, using the Korean VLBI Network at 22 and 43 GHz and gamma-ray data from the Fermi Large Area Telescope (LAT). Our findings reveal spectral variations around the 2014 gamma-ray flare, aligning with the shock-in-jet model. A strong correlation is observed between gamma-ray and 43 GHz emissions, with a 27-day lag in the VLBI core light curve, indicating a 50-day delay from the beginning of a specific radio flare to the gamma-ray peak. This radio flare correlates with a new jet component, suggesting the 2014 gamma-ray flare resulted from its interaction with a stationary component. Our analysis indicates the 2014 gamma-ray flare originated 40-63 parsecs from the central engine, with seed photons for the gamma-ray emission unlikely from the broad-line region.
16
- Seonjae Lee
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.163-171
- 2024
- 원문 바로보기
Hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) are isomers with similar chemical properties. However, HNC can be converted into other molecules by reactions with atomic hydrogen (H) and atomic oxygen (O), resulting in a variation of the HCN/HNC abundance ratio. These reaction rates are sensitive to gas temperature, resulting in different abundance ratios in different temperature environments. The emission of HCN and HNC was found to distribute along ring structures in the protoplanetary disk of V883 Ori. HCN exhibits a multi-ring structure consisting of inner and outer rings. The outer ring represents a genuine chemical structure, whereas the inner ring appears to display such characteristics due to the high dust continuum optical depth at the center. However, HNC is entirely depleted in the warmer inner ring, while its line intensity is similar to that of HCN in the colder outer ring. In this study, we present a chemical calculation that reproduces the observed HCN/HNC abundance ratio in the inner and outer rings. This calculation suggests that the distinct emission distribution between HCN and HNC results from a currently ongoing outburst in V883 Ori. The sublimation of HCN and HNC from grain surfaces and the conversion of HNC to HCN determine their chemical distribution in the heated, warm inner disk.
17
- Joon Hyeop Lee
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.105-114
- 2024
- 원문 바로보기
Full spectrum fitting is a powerful tool for estimating the stellar populations of galaxies, but the fitting results are often significantly influenced by internal dust attenuation. For understanding how the choice of the internal dust correction method affects the detailed stellar populations estimated from the full spectrum fitting, we analyze the Sydney-Australian Astronomical Observatory Multi-object Integral field spectrograph (SAMI) galaxy survey data using the Penalized PiXel-Fitting (PPXF) package. Three choices are compared: (Choice-1) using the PPXF reddening option, (Choice-2) using the multiplicative Legendre polynomial, and (Choice-3) using none of them (no dust correction). In any case, the total mean stellar populations show reasonable mass-age and mass-metallicity relations (MTR and MZR), although the correlations appear to be strongest for Choice-1 (MTR) and Choice-2 (MZR). When we compare the age-divided mean stellar populations, the MZR of young (<10<sup>9.5</sup> yr ≈ 3.2 Gyr) stellar components in Choice-2 is consistent with the gas-phase MZR, whereas those in the other two choices hardly are. On the other hand, the MTR of old (≥10<sup>9.5</sup> yr) stellar components in Choice-1 seems to be more reasonable than that in Choice-2, because the old stellar components in low-mass galaxies tend to be relatively younger than those in massive galaxies. Based on the results, we provide empirical guidelines for choosing the optimal options for dust correction.
18
- Dohyeong Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.95-103
- 2024
- 원문 바로보기
In the merger-driven galaxy evolution scenario, dust-obscured quasars are considered to be an intermediate population between merger-driven star-forming galaxies and unobscured quasars; however, this scenario is still controversial. To verify this, it is necessary to investigate whether dust-obscured quasars have higher Eddington ratio (λ<sub>Edd</sub>) values than those of unobscured quasars, as expected in the merger-driven galaxy evolution scenario. In this study, we derive black hole (BH) masses of 10 dust-obscured quasars at z ~ 2, during the peak period of star-formation and BH growth in the Universe, using a newly derived mid-infrared (MIR) continuum luminosity (L<sub>MIR</sub>)-based estimator that is highly resistant to dust extinction. Then, we compare the λ<sub>Edd</sub> values of these dust-obscured quasars to those of unobscured type-1 quasars at similar redshifts. We find that the measured log (λ<sub>Edd</sub>) values of the dust-obscured quasars, -0.06 ± 0.10, are significantly higher than those of the unobscured quasars, -0.86 ± 0.01. This result remains consistent across the redshift range from 1.5 to 2.5. Our results show that the dust-obscured quasars are at their maximal growth, consistent with the expectation from the merger-driven galaxy evolution scenario at the epoch quasar activities were most prominent in the cosmic history.
19
- Changmin Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.11-11
- 2024
- 원문 바로보기
The following sentence was erroneously dropped from the acknowledgment: This work was supported by Chungnam National University. The corrected text is listed below; it should replace the Acknowledgements section.
20
- Yong-Jae Moon
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.35-44
- 2024
- 원문 바로보기
The Sun-Earth Lagrange point L4, which is called a parking space of space, is considered one of the unique places where solar activity and the heliospheric environment can be observed continuously and comprehensively. The L4 mission affords a clear and wide-angle view of the Sun-Earth line for the study of Sun-Earth connections from remote-sensing observations. The L4 mission will significantly contribute to advancing heliophysics science, improving space weather forecasting capability, extending space weather studies far beyond near-Earth space, and reducing risk from solar radiation hazards on human missions to the Moon and Mars. Our paper outlines the importance of L4 observations by using remote-sensing instruments and advocates comprehensive and coordinated observations of the heliosphere at multi-points including other planned L1 and L5 missions. We mainly discuss scientific perspectives on three topics in view of remote sensing observations: (1) solar magnetic field structure and evolution, (2) source regions of geoeffective solar energetic particles (SEPs), and (3) stereoscopic views of solar corona and coronal mass ejections (CMEs).