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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
- Kyung-Won Suh
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.123-134
- 2024
- 원문 바로보기
We investigate the properties of AGB and post-AGB (PAGB) stars, planetary nebulae, and young stellar objects (YSOs) in our Galaxy through an analysis of observational data covering visual and infrared (IR) wavelengths. Utilizing datasets from IRAS, 2MASS, AllWISE, Gaia DR3, and the SIMBAD object database, we perform an in-depth comparison between observational data and theoretical models. For this comparison, we present various color-magnitude diagrams (CMDs) in visual and IR bands, as well as IR two-color diagrams (2CDs). Our results demonstrate that the CMDs, incorporating the latest distance and extinction data from Gaia DR3 for a majority of sample stars, are effective in distinguishing different classes of stars. To improve the precision of our analysis, we apply theoretical radiative transfer models for dust shells around AGB and PAGB stars. A thorough comparison of the theoretical models with observations across various IR 2CDs and CMDs shows a significant agreement. We find that AGB and PAGB stars are among the brightest classes in visual and IR bands. Furthermore, most YSOs are clearly distinguishable from AGB stars on various IR CMDs, exhibiting fainter absolute magnitudes in IR bands.
12
- So-Myoung Park
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.211-221
- 2024
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We investigate the evolution of initial fractal clusters at 3 kpc from the Galactic Center (GC) of the Milky Way and show how red supergiant clusters (RSGCs)-like objects, which are considered to be the result of active star formation in the Scutum complex, can form by 16 Myr. We find that initial tidal filling and tidal over-filling fractals are shredded by the tidal force, but some substructures can survive as individual subclusters, especially when the initial virial ratio is ≤0.5. These surviving subclusters are weakly mass segregated and show a top-heavy mass function. This implies the possibility that a single substructured star cluster can evolve into multiple 'star clusters'.
13
- Hyojun Lee
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.1-9
- 2024
- 원문 바로보기
Korean historical literatures offer numerous records on astronomical phenomena such as eclipses, comets, and close approaches, etc. Records of close approaches often use specific terms to describe the angular distance, which lack translation into modern numerical values. We study the usage of the five commonly used terms, namely, Entry (入, En), Invasion (犯, In), Occultation (掩, Oc), Eclipse (食, Ec), as well as the unit Chi (尺). Our analysis is based on more than 2,300 records from Goryeo (918-1392 CE) and Joseon (1392-1910 CE) Dynasties. Through statistical analysis, we determine their quantitative definitions. We convert the lunisolar calendar to the Julian and Gregorian date and utilize the modern ephemeris DE431 to calculate the angular distance between celestial bodies. We find that the angular distances of the terms En, In, Oc, and Ec correspond to respectively 1.78°<sup>+2.36</sup><sub>-1.11</sub>, 0.89°<sup>+3.54</sup><sub>-0.51</sub>, 0.44°<sup>+1.15</sup><sub>-0.31</sub>, and 0.29°<sup>+2.61</sup><sub>-0.16</sub> for the Goryeo Dynasty and 1.36°<sup>+1.15</sup><sub>-0.64</sub>, 0.51°<sup>+1.11</sup><sub>-0.32</sub>, 0.25°<sup>+0.27</sup><sub>-0.17</sub>, and 0.21°<sup>+0.25</sup><sub>-0.11</sub> for the Joseon Dynasty. Additionally, we determine the angular size of the unit Chi by using the records from Korean chronicles along with the drawings of comets' tails in the Daily Log (天變謄錄). We estimate the unit Chi to be 1.11°<sup>+0.46</sup><sub>-0.40</sub> and find that the numerical definition was consistent throughout the two dynasties in Korea. Furthermore, we find that the terms were used to describe the closest approach and that there is no observational bias in the angular distances against the apparent magnitudes of the objects. We show that the terms En, In, Oc, and Ec represent decreasing angular distance in that order and this ordering was consistent in both dynasties.
14
- Gwangeon Seong
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.115-122
- 2024
- 원문 바로보기
Carbon fusion is important to understand the late stages in the evolution of a massive star. Astronomically interesting energy ranges for the <sup>12</sup>C+<sup>12</sup>C reactions have been, however, poorly constrained by experiments. Theoretical studies on stellar evolution have relied on reaction rates that are extrapolated from those measured in higher energies. In this work, we update the carbon fusion reaction rates by fitting the astrophysical S-factor data obtained from direct measurements based on the Fowler, Caughlan, & Zimmerman (1975) formula. We examine the evolution of a 20 M<sub>⊙</sub> star with the updated <sup>12</sup>C+<sup>12</sup>C reaction rates performing simulations with the MESA (Modules for Experiments for Stellar Astrophysics) code. Between 0.5 and 1 GK, the updated reaction rates are 0.35 to 0.5 times less than the rates suggested by Caughlan & Fowler (1988). The updated rates result in the increase of core temperature by about 7% and of the neutrino cooling by about a factor of three. Moreover, the carbon-burning lifetime is reduced by a factor of 2.7. The updated carbon fusion reaction rates lead to some changes in the details of the stellar evolution model, their impact seems relatively minor compared to other uncertain physical factors like convection, overshooting, rotation, and mass-loss history. The astrophysical S-factor measurements in lower energies have large errors below the Coulomb barrier. More precise measurements in lower energies for the carbon burning would be useful to improve our study and to understand the evolution of a massive star.
15
- Kyung-Chan Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.197-210
- 2024
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The Earth's radiation belts, which extend from near the Earth to approximately geosynchronous orbit, contain highly energetic particles that actively interact with various plasma waves. This study reviews two numerical approaches to studying wave-particle interactions in the Earth's radiation belts and discusses their respective advantages and limitations. The first approach involves diffusion simulations based on quasi-linear theory, which is well-suited for describing the collective dynamics of many particles from a statistical perspective. The second approach, test particle simulation, focuses on the detailed motion of individual particles, revealing nonlinear phenomena such as phase trapping and bunching. Both methods allow for the derivation of diffusion coefficients, which quantify the timescale of wave-particle interactions and help explain how particles either precipitate into the atmosphere or accelerate to higher energies in the Earth's radiation belts. Additionally, these methodologies can be adapted to study the dynamics of planetary radiation belts, such as those around Jupiter and Saturn, by adjusting for the specific environmental parameters of each planet.
16
- Sungshil Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.173-182
- 2024
- 원문 바로보기
Forbush decreases (FDs), as the transient event of decreasing cosmic ray (CR) intensity, show the main phase of a sudden decrease within approximately one day and the recovery phase over several days. FDs are associated with abrupt solar wind events such as interplanetary shocks (IP shocks) and magnetic clouds. FD generation is explained by drift due to the magnetic field strength and by diffusion caused by magnetic turbulence. The FDs and the IP shocks from 1998 to 2004 in the solar maximum period were chosen to determine a more effective generation of FD between drift and diffusion. Seventy FDs with a CR variation of more than 3.0% and a minimum value of less than -1.5% were selected using Oulu neutron monitor data. The Advanced Composition Explorer satellite identified 292 IP shocks and we divided them into two sections: the pre-sheath region ahead of the shock front and the post-sheath region behind the shock front. The magnetic field strength, magnetic turbulence, solar wind speed, and solar wind turbulence of the post-sheath regions were analyzed. Most (62/70) of the FDs were associated with the post-sheath regions of the IP shocks. The important factors that generated the FDs were drift by the large physical properties in the post-sheath regions and diffusion by the strong turbulence in the post-sheath regions. The increase in the magnitude of interplanetary magnetic field (IMF) shows larger in the IP shocks associated with FD (2.33 times) than in those not associated with an FD (1.70 times) between the pre-sheath and post-sheath regions. On the other hand, the increase in turbulence of IMF was the same for IP shocks associated with an FD and not associated with an FD. Although it was difficult to determine the dominant factor for the generation of FDs, the present study suggested that the drift by the magnetic field strength may play a more significant role than the diffusion by the magnetic turbulence.
17
- Tetsuya Magara
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.239-247
- 2024
- 원문 바로보기
We investigated dynamic interaction between adjacent magnetic loops in the solar atmosphere, which is a process of volume shrinkage with nonuniform acceleration caused by Lorentz force. When these loops locally have different thermal and dynamic properties, a significant discrepancy between their translational motions driven by means of that force may arise, leading to the dynamic interaction. We use both numerical simulation and analytic model of magnetic piston-driven wave to evaluate how much a single event of the interaction contributes to increasing the temperature in the upper chromosphere. The model shows a possibility that a chromospheric plasma is heated by the single event to have transition region temperature, which is typically several tens of times higher than chromospheric temperature. The model also provides an insight into the formation height of the transition region.
18
- Hyesung Kang
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.55-66
- 2024
- 원문 바로보기
This study investigates the impact of magnetic turbulence on cosmic ray (CR) electrons through Fermi-II acceleration behind merger-driven shocks in the intracluster medium and examines how the ensuing synchrotron radio emission is influenced by the decay of magnetic energy through dissipation in the postshock region. We adopt simplified models for the momentum diffusion coefficient, specifically considering transit-time-damping resonance with fast-mode waves and gyroresonance with Alfvén waves. Utilizing analytic solutions derived from diffusive shock acceleration theory, at the shock location, we introduce a CR spectrum that is either shock-injected or shock-reaccelerated. We then track its temporal evolution along the Lagrangian fluid element in the time domain. The resulting CR spectra are mapped onto a spherical shell configuration to estimate the surface brightness profile of the model radio relics. Turbulent acceleration proves to be a significant factor in delaying the aging of postshock CR electrons, while decaying magnetic fields have marginal impacts due to the dominance of inverse Compton cooling over synchrotron cooling. However, the decay of magnetic fields substantially reduces synchrotron radiation. Consequently, the spatial distribution of the postshock magnetic fields affects the volume-integrated radio spectrum and its spectral index. We demonstrate that the Mach numbers estimated from the integrated spectral index tend to be higher than the actual shock Mach numbers, highlighting the necessity for accurate modeling of postshock magnetic turbulence in interpreting observations of radio relics.
19
- 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.
20
- Eunjin Cho
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.83-94
- 2024
- 원문 바로보기
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.