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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
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1
- 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.
2
- Kyung-Chan Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.197-210
- 2024
- 원문 바로보기
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.
3
- 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.
4
- Yun-A Jo
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.145-154
- 2024
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In this paper, we investigate asteroseismic scaling-relations of evolved stars in star clusters observed by Kepler/K2, aiming to address the issue of whether observed stellar oscillations are influenced by environmental factors, as there are interesting phenomena relating to the stellar pulsations observed in star clusters. Specifically, we compare statistical properties of distributions including ∆𝜈, 𝜈<sub>max</sub>, H<sub>Gauss</sub>, 𝛿𝜈<sub>env</sub>, and 𝛿𝜈<sub>02</sub> derived from red giant branch (RGB) and red clump (RC) stars in two pairs of star clusters: NGC 2682 - NGC 6819 and NGC 1817 - NGC 6811. We have found that the slopes of relations between 𝜈<sub>max</sub> and ∆𝜈 and between H<sub>Gauss</sub> and 𝜈<sub>max</sub> associated with RC stars in the more compact star clusters, NGC 2682 and NGC 1817, are in common less steep compared with those for NGC 6819 and NGC 6811. It is also found that the slopes of the relation between 𝛿𝜈<sub>env</sub> and 𝜈<sub>max</sub> from RC stars in the more compact star clusters are in common steeper compared with those for the others. For the relation between 𝛿𝜈<sub>02</sub> and ∆𝜈 obtained from RGB stars, the slope resulting from NGC 2682 and NGC 6819 is indistinguishable. The Kolmogorov-Smirnov tests conducted on RC stars in the pairs of NGC 2682 and NGC 6819, as well as NGC 1817 and NGC 6811, indicate that all the seismic quantities considered in this paper are drawn from different distributions. We conclude, therefore, that the properties of star clusters should be considered when asteroseismic data obtained from stars within star clusters are interpreted.
5
- Hyesung Kang
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.155-162
- 2024
- 원문 바로보기
During the formation of large-scale structures in the universe, weak internal shocks are induced within the hot intracluster medium (ICM), while strong accretion shocks arise in the warm-hot intergalactic medium (WHIM) within filaments, and the warm-cold gas in voids surrounding galaxy clusters. These cosmological shocks are thought to accelerate cosmic ray (CR) protons and electrons via diffusive shock acceleration (DSA). Recent advances in particle-in-cell and hybrid simulations have provided deeper insights into the kinetic plasma processes that govern microinstabilities and particle acceleration in collisionless shocks in weakly magnetized astrophysical plasma. In this study, we adopt a thermal-leakage type injection model and DSA power-law distribution functions in the test-particle regime. The CR proton spectrum directly connects to the Maxwellian distribution of protons at the injection momentum p<sub>inj</sub> = Q<sub>p</sub>p<sub>th,p</sub>. On the other hand, the CR electron spectrum extends down to p<sub>min</sub> = Q<sub>e</sub>p<sub>th,e</sub> and is linked to the Maxwellian distribution of electrons. Here, p<sub>th,p</sub> and p<sub>th,e</sub>, are the proton and electron thermal momenta, respectively. Moreover, we propose that the postshock gas temperature and the injection parameters, Q<sub>p</sub> and Q<sub>e</sub> are self-regulated to maintain the test-particle condition, as the thermal energy is gradually transferred to the CR energy. Under these constraints, we estimate the self-regulated values of the temperature reduction factor, R<sub>T</sub>, and the proton injection parameter, Q<sub>p</sub>, along with the resulting CR efficiencies, 𝜂<sub>p</sub> and 𝜂<sub>e</sub>. We then provide analytical fitting functions for these parameters as functions of the shock Mach number, M<sub>s</sub>. These fitting formulas may serve as valuable tools for quantitatively assessing the impact of CR protons and electrons, as well as the resulting nonthermal emissions in galaxy clusters and cosmic filaments.
6
- Jongyeob Park
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.183-196
- 2024
- 원문 바로보기
The Balloon-borne Investigation of Temperature and Speed of Electrons in the corona (BITSE) mission, performed by KASI and NASA, used a high-altitude scientific balloon. The purpose of BITSE was to investigate the scientific feasibility of electron temperature and velocity measurements in the solar corona using wavelength-dependent polarization brightness differences. KASI was responsible for developing the command and data handling (C&DH) system, including the main electronics unit and flight software (FSW). Here, we introduce the development of C&DH system of BITSE and describe the ground integration and test and flight operations. The main electronics unit was built using an industrial-grade modular system in customized enclosures that withstood the operating environment. The FSW was developed using the core Flight System (cFS), an open-source software framework developed by NASA and used in several successful space missions. BITSE was launched at Fort Sumner, New Mexico, USA, on September 18, 2019. It observed the solar corona for approximately 4 hours at an altitude of approximately 40 km and collected 16,000 solar corona images. This study could provide guidelines for developing the C&DH system for future balloon missions.
7
- 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.
8
- 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.
9
- 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.
10
- Jiwon Park
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.223-237
- 2024
- 원문 바로보기
This study employs a range of AI-based bibliometric methods to examine trends among astronomical research publications. Astronomy is a field with a long history of research and a wide variety of fields, so there are many areas in which quantitative bibliometric studies can be used to categorize topics, summarize research trends, and explore future research directions. For our first attempt we chose the oldest astronomical instrument, the sundial. We collected a total of 172 sundial and gnomon research papers from 1909 to 2024 from Web of Science and Scopus databases. A bibliometric analysis of the astronomical research papers was performed using the bibliometrix package in R. Topics were categorized and discussed using the Structural Topic Model (STM) method. Productivity, citation counts, and other metrics were compared across countries and journals and the global network of researchers engaged in the study of sundials was analyzed. Results emphasize the need for greater international collaboration and interdisciplinary integration. Current trends in sundial and gnomon research were reviewed, identifying eight research topics through the use of STM, demonstrating the evolution of this field into various applications. The article concludes by discussing future research directions for sundials and gnomons, demonstrating the applicability of AI-assisted bibliometric analysis in various fields of astronomy research.