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1968년 ~ 2025년까지 1,227 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 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 3/123
21
- 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.
22
- 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.
23
- 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.
24
- 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.
25
- 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.
26
- 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.
27
- Jeongwhan Han
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.25-33
- 2024
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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.
28
- 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.
29
- 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.
30
- Shan Li
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.67-82
- 2024
- 원문 바로보기
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.