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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
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11
- Daye Lim
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.2
- pp.197-207
- 2025
- 원문 바로보기
We present a comprehensive solar flare forecast model with a probability and a statistically significant range of daily peak X-ray flux. For this, we consider 𝜇-corrected total unsigned radial magnetic fluxes from the SOHO/MDI and SDO/HMI, and flare lists from GOES from 1996 to 2021. Our model predicts two types of forecast results when a magnetic flux of an active region (AR) is given. First, using a relationship between magnetic fluxes and flaring rates, a probability of C1.0 or greater flares and a probability of M1.0 or greater flares within a day are predicted respectively. Second, a mean (𝜇) and standard deviation (𝜎) of daily peak X-ray fluxes are given from a historical distribution between magnetic fluxes and daily peak X-ray fluxes. Using the mean and standard deviation, we provide the statistical range of possible flare sizes. We verify two forecast results by using various performance metrics and investigate the performance depending on the climatology event rate. Based on the metric values, our model can give a better performance than the climatology forecast. Solar flares are considered to be caused by specific triggers and physical mechanisms that have not yet been precisely identified. In addition, there is another perspective that the size of the flare that will occur due to a trigger is close to random because the flaring loop is in a self-organized critical state. Our model can give the simplest forecasting results considering these two perspectives.
12
- Jae Woo Lee
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.1
- pp.99-110
- 2025
- 원문 바로보기
Photometric and spectroscopic observations of GV Leo were performed from 2017 to 2024. The light curves show a flat bottom at the primary eclipse and the conventional O'Connell effect. The echelle spectra reveal that the effective temperature and rotation velocity of the more massive secondary are T<sub>eff,2</sub> = 5220 ± 120 K and v<sub>2</sub> sin i = 223 ± 40 km s<sup>-1</sup>, respectively. Our binary modeling indicates that the program target is a W-subclass contact binary with a mass ratio of q = 5.48, an inclination angle of i = 81.°68, a temperature difference of (T<sub>eff,1</sub> - T<sub>eff,2</sub>) = 154 K, and a filling factor of f = 36%. The light asymmetries were reasonably modeled by a dark starspot on the secondary's photosphere. Including our 26 minimum epochs, 84 times of minimum light were used to investigate the orbital period of the system. We found that the eclipse times of GV Leo have varied by a sinusoid with a period of 14.9 years and a semi-amplitude of 0.0076 days superimposed on a downward parabola. The periodic modulation is interpreted as a light time effect produced by an unseen outer tertiary with a minimum mass of 0.26 M<sub>⊙</sub>, while the parabolic component is thought to be a combination of mass transfer (secondary to primary) and angular momentum loss driven by magnetic braking. The circumbinary tertiary would have caused the eclipsing pair of GV Leo to evolve into its current short-period contact state by removing angular momentum from the primordial widish binary.
13
- Dongwook Lim
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.1
- pp.81-92
- 2025
- 원문 바로보기
Recent advancements in near-infrared (NIR) spectroscopy have opened new opportunities for studying multiple stellar populations in globular clusters (GCs), particularly for newly discovered clusters in the inner Milky Way. While optical spectroscopy has traditionally played a primary role in detailed chemical abundance studies of GCs, the increasing discovery of GCs in highly reddened environments underscores the need for robust NIR spectroscopic methods. To evaluate the utility of high-resolution NIR spectroscopy for studying multiple stellar populations, we observed six stars in M5, a well-studied halo GC, using the recently commissioned IGRINS-2 spectrograph on the Gemini-North telescope. Our chemical abundance measurements in the NIR wavelength range show good agreement with those derived from high-resolution optical spectroscopy, with minor systematic offsets in elements such as Na and Mg. In addition, the measured chemical abundance ratios clearly reproduce the distinctive patterns of multiple stellar populations, including the Na-O anti-correlation. The ability of NIR spectroscopy to measure C, N, and O abundances with high precision further enhances its utility for studying chemical properties of stars and GCs. Our findings demonstrate that IGRINS-2 and similar instruments have significant potential to advance our understanding of GC formation, stellar chemical evolution, and the evolutionary history of the Milky Way.
14
- Sung-Moon Yoo
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.2
- pp.265-280
- 2025
- 원문 바로보기
This study introduces a refined method for accurately determining the Invariant Point (IVP) of Very Long Baseline Interferometry (VLBI) antennas through constrained optimization, emphasizing the critical role of axis-offset sign conditions. Optical surveying techniques, commonly used to determine IVPs, inherently involve measurement limitations and observational errors, which may lead to biased estimations of the Azimuth (AZ) and Elevation (EL) axes. To mitigate these biases, we implement physical geometric constraints, including equal-radius conditions for target circles and equal inter-circle distances to ensure consistency across multiple Azimuth positions. Our method specifically incorporates a novel approach for determining the axis-offset sign, which significantly influences VLBI delay estimations. To validate the effectiveness of our method, we conducted numerical simulations using a virtual model with a predefined IVP and axis configuration. Realistic measurement noise was introduced to generate synthetic observational data. Simulation results clearly show that our constrained optimization approach substantially reduces bias and variance in IVP estimation compared to the geometric method proposed in our previous work. Specifically, the proposed method reduced the 3D RMSE of IVP estimation by approximately 40% (e.g., from 1.239 mm to 0.736 mm at 50 m observation distance) and the Interquartile Range (IQR) Error Norm by over 60% (e.g., from 0.949 mm to 0.343 mm at 50 m observation distance). The proposed method's explicit handling of axis-offset sign conditions demonstrates originality and practical applicability, providing robust and reliable antenna reference point determination. Furthermore, we successfully applied this refined method to the Korean VLBI Network (KVN) Pyeongchang VLBI antenna, demonstrating practical effectiveness in operational geodetic VLBI environments. This advancement contributes to enhanced precision in International Terrestrial Reference Frame (ITRF) realization through improved VLBI station positioning.
15
- Hosung Lim
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.1
- pp.43-53
- 2025
- 원문 바로보기
Galaxy evolution studies require the measurement of the physical properties of galaxies at different redshifts. In this work, we build supervised machine learning models to predict the redshift and physical properties (gas-phase metallicity, stellar mass, and star formation rate) of star-forming galaxies from the broad-band and medium-band photometry covering optical to near-infrared wavelengths, and present an evaluation of the model performance. Using 55 magnitudes and colors as input features, the optimized model can predict the galaxy redshift with an accuracy of σ<sub>(Δz/1+z)</sub> = 0.008 for a redshift range of z < 0.4. The gas-phase metallicity [12 + log(O/H)], stellar mass [log(M<sub>star</sub>)], and star formation rate [log(SFR)] can be predicted with the accuracies of σ<sub>NMAD</sub> = 0.081, 0.068, and 0.19 dex, respectively. When magnitude errors are included, the scatter in the predicted values increases, and the range of predicted values decreases, leading to biased predictions. Near-infrared magnitudes and colors (H, K, and H - K), along with optical colors in the blue wavelengths (m425-m450), are found to play important roles in the parameter prediction. Additionally, the number of input features is critical for ensuring good performance of the machine learning model. These results align with the underlying scaling relations between physical parameters for star-forming galaxies, demonstrating the potential of using medium-band surveys to study galaxy scaling relations with large sample of galaxies.
16
- Daya Nidhi Chhatkuli
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.1
- pp.93-98
- 2025
- 원문 바로보기
Scaling relations are fundamental tools for exploring the morphological properties of galaxies and understanding their formation and evolution. Typically, galaxies follow a scaling relation between mass and size, measured by effective radius. However, a compact class of galaxies exists as outliers from this relation, and the origin of these compact galaxies in the local universe remains unclear. In this study, we investigate the compact dwarf galaxy SDSS J134313.15+364457.5 (J1343+3644), which is the result of a merger. Our analysis reveals that J1343+3644 has a half-light radius of 482 pc, significantly smaller than typical galaxies with the same brightness (M<sub>r</sub> = -19.17 mag). With a high star-formation rate (SFR) of 0.87 M<sub>⊙</sub> year<sup>-1</sup>, J1343+3644 is expected to evolve into a compact elliptical galaxy in a few million years. J1343+3644 could, therefore, be a progenitor of a compact elliptical galaxy. The phenomenon happened in early universe, where compact galaxies were common.
17
- 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.
18
- 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.
19
- 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.
20
- Yun-A Jo
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.145-154
- 2024
- 원문 바로보기
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.