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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
- 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.
2
- 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.
3
- Jongyeob Park
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.183-196
- 2024
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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.
4
- 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.
5
- 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.
6
- 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.
7
- Dohyeong Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.95-103
- 2024
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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.
8
- 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.
9
- 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.
10
- 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.