간행물
천문학회지 KCI 등재 SCOPUS Journal of The Korean Astronomical Society
- 발행기관 한국천문학회
- 자료유형 학술지
- 간기 반년간
- ISSN 1225-4614 (Print)2288-890X (Online)
- 수록기간 1968 ~ 2026
- 주제분류 자연과학 > 천문학 자연과학 분류의 다른 간행물
- 십진분류KDC 440DDC 520
권호리스트/논문검색
제59권 제2호 (2026년 7월) 9건
1.
2026.07
구독 인증기관 무료, 개인회원 유료
Younghun Oh, Seo-Won Chang, Jongchul Chae, Juhyung Kang, Soosang Kang, Kyeore Lee, Kyoung-Sun Lee, Eun-Kyung Lim, Hyun-Il Sung
Active M dwarfs exhibit frequent and energetic flares that provide a unique laboratory for studying chromospheric heating processes under extreme magnetic activity. To probe the flare process of M-dwarfs, we present a high-resolution (R ∼ 30,000) spectroscopic case study of a superflare onADLeo, detected on 2023 March 14 using the Bohyunsan Optical Echelle Spectrograph (BOES). Such high-energy events are rarely captured with simultaneous multi-line spectroscopy, allowing us to trace the energy partition and temporal evolution of the chromospheric lines. Based on equivalent width variations, we found that the Hα line radiated 8.8×1030 erg, implying a total bolometric energy (∼1033 erg) comparable to the largest solar flares. The Balmer series dominated the energy budget; the individual Ca ii H and K lines contributed 47.5% and 26.2% of the Hα energy, respectively, while each Ca ii infrared triplet line emitted ∼17–19%. We confirm that the delayed peak emission, previously reported for Ca ii H&K, also occurs in the Ca ii triplet and Na i lines. These delays are consistent with the Neupert effect, suggesting that cumulative heating governs the gradual phase emission. While this superflare resembled solar flares in its general morphology, it also displayed systematic differences in chromospheric emission. It is likely that these differences reflect the distinct atmospheric structure and quiescent chromospheric conditions of M dwarfs, rather than fundamentally different flare physics.
4,500원
2.
2026.07
구독 인증기관 무료, 개인회원 유료
Sang-Hee Kim, Byeong-Cheol Lee, Shenghong Gu, Jae-Rim Koo, Beomdu Lim, Myeong-Gu Park, Huan-Yu Teng, Yeon-Ho Choi, David Mkrtichian, Tae-Yang Bang, Hyeong-Ill Oh, Heon-Young Chang
Detecting planetary companions around evolved stars, particularly asymptotic giant branch (AGB) stars, is challenging due to intrinsic stellar variability such as surface convection, pulsations, and mass loss, which can produce radial velocity (RV) signals that mimic Keplerian motion. We investigate the origin of the long-period, low-amplitude RV variations observed in the AGB star HD 216595 using high-resolution spectroscopic data spanning approximately 16 years obtained with the Bohyunsan Optical Astronomy Observatory Echelle Spectrograph (BOES) and the Las Cumbres Observatory Network of Robotic Echelle Spectrographs (NRES) instruments. The RV measurements reveal a statistically significant periodic signal with a period of 567 days that can be described by a Keplerian model consistent with a substellar companion. However, no strong correlations are found between the RV variations and stellar activity indicators, including line bisectors, chromospheric activity, and photometric variability, although weak signals on similar timescales are present in some diagnostics. Given the stellar properties of HD 216595 and its similarities to previously reported cases, the observed RV variations are likely related to intrinsic stellar processes, although a companion-induced origin cannot be definitively ruled out. Further progress will require improved diagnostics and more sophisticated modeling to disentangle stellar variability from genuine orbital signals.
4,200원
3.
2026.07
구독 인증기관 무료, 개인회원 유료
Jiseop Shin, Mankeun Jeong, Myungshin Im, Seo-Won Chang, Sang-Mok Cha, Seong-Kook Lee
Astronomical CCD images are often affected by bleeding from bright sources, producing column-aligned streaks that degrade source detection and photometry. We present a pixel-level masking algorithm for bleeding in Korea Microlensing Telescope Network (KMTNet) images, in which these streaks extend along detector columns away from the readout register. The algorithm identifies bleed-generating pixels using a conservative bleeding threshold and a bleeding index that quantifies excess signal along the expected bleeding direction. The extent of each bleed trail is then determined by termination criteria based on a backgroundrelative detection threshold and a continuity condition. To optimize these termination parameters, we generate multiple candidate masks and evaluate them with an Fβ-like score that favors high purity while preserving recovery of sources whose photometry is biased by bleeding. Using the final mask, we apply interpolation-based cleaning and assess the performance in terms of completeness and photometric accuracy in a crowded KMTNet field, using Gaia DR3 as a reference. The source completeness improves from 94.08% to 98.61%, primarily by enabling proper aperture placement that was previously hindered by bleeding. For selected bleeding-affected sources, the root-mean-square photometric offset decreases from 0.623 mag to 0.068 mag. These results demonstrate that the algorithm provides a practical framework for mitigating bleeding artifacts in KMTNet images. We further examine the stability of the algorithm across different observing conditions and discuss limitations of the current masking and cleaning procedure.
4,500원
4.
2026.07
구독 인증기관 무료, 개인회원 유료
Young-Bin Shin, Sang-Sung Lee, Sincheol Kang, Whee Yeon Cheong, Chanwoo Song, Jeffrey A. Hodgson
In this study, we estimated the angular diameter distances to two high-redshift active galactic nuclei (AGNs), OJ 248 (z = 0.939) and 4C +38.41 (z = 1.814), using 43 GHz radio light curves. The aim of this work is to extend AGN variability–based distance measurement methods to the high-redshift regime. The distance estimates were analyzed under two assumptions for the maximum intrinsic brightness temperature TB, int: (1) the equipartition temperature, and (2) the sample-averaged TB, int. As a representative result, when adopting the equipartition temperature, the angular diameter distances to OJ 248 and 4C +38.41 are estimated to be 7,592.7±396.7 Mpc and 11,069.8±1,216.9 Mpc, respectively. In addition, Doppler factors were calculated using the inverse-Compton method, and additional distance estimates were obtained based on these values. Our error budget analysis shows that the most significant systematic uncertainty arises from epoch selection. These results indicate that systematic effects have a substantial impact on the derived distance estimates and limit their reliability, particularly in the high-redshift regime. Reducing these uncertainties will require improved observational cadence and reduced post-fit noise. AGN variability provides an alternative approach to distance estimation. However, our results reveal significant limitations in the current methodology and indicate that further methodological and observational improvements are required before its cosmological applicability can be reliably assessed.
4,000원
5.
2026.07
구독 인증기관 무료, 개인회원 유료
Byeong-Cheol Lee, Myeong-Gu Park
We present precise radial-velocity (RV) observations of the K-type red supergiant HD 216946 (V424 Lac) obtained over approximately 22 years with the Bohyunsan Optical Astronomy Observatory Echelle Spectrograph (BOES). TheRVmeasurements reveal significant long-period variability with a period of 1,365 days. To investigate its origin, we analyzed the RV data together with line-profile variations (LPVs), chromospheric activity indicators, and published photometric variability. The LPVs exhibit periods of approximately 1,370–1,380 days, while the Na D lines show a similar periodicity near 1,355 days, both comparable to the RV period. In contrast, the H-line indicators display longer periods of 2,730–2,800 days, approximately twice the RV period. The close correspondence between the RV variations and the activity-related diagnostics strongly suggests that the 1,365-day RV signal is primarily linked to chromospheric activity and extended atmospheric variability rather than arising from purely Keplerian motion. Published photometric studies also report additional long-period variability, including a 1,601-day long secondary-period (LSP)-like variation. The coexistence of multiple non-identical periods indicates that the observed variability of HD 216946 is unlikely to originate from a single physical mechanism. We therefore interpret HD 216946 as a multiperiodic red supergiant in which several intrinsic stellar processes coexist. The observed variability is most likely dominated by chromospheric activity and large-scale atmospheric dynamics, possibly accompanied by rotational modulation and LSP-like variability, although the presence of a low-mass stellar companion cannot be completely excluded.
4,000원
6.
2026.07
구독 인증기관 무료, 개인회원 유료
Junho Song, Hyunmi Song, Hyunjin Shim
Hydrogen recombination lines, one of the strongest emission lines from star-forming galaxies, are used to probe the early Universe as indicators of star formation rates and ionizing photon production rates. Ratios between different recombination lines provide clues for estimating dust attenuation, in addition to the HII region physical diagnostics. To prepare for future near-infrared spectral surveys and optical narrow-band imaging surveys aiming for hydrogen lines at different redshifts, we construct hydrogen recombination line libraries by compiling data from published literature. Our compilation includes 260 galaxies mostly at z ≲ 0.4, of which at least one hydrogen recombination line is observed. The specific hydrogen emission lines under investigation encompass three Balmer lines (Hα, Hβ and Hγ) and the Lyα line. Of the compiled galaxies, we estimated dust extinction for 85 galaxies that have detections of at least two Balmer lines, by assuming Case B recombination and Calzetti extinction curve, based on which Lyα escape fraction is also inferred. For each of the 14 galaxies with detections of all three Balmer lines, we optimized the extinction curve so that it yields consistent E(B − V ) values across the three possible Balmer line ratios, showing the variety in the slope of the dust attenuation curve. We further evaluated the feasibility of studying hydrogen emission line-selected galaxies with future spectral surveys such as SPHEREx by modeling the Paschen lines of our galaxy sample.
4,800원
7.
2026.07
구독 인증기관 무료, 개인회원 유료
Gilgu Kang, Ahra Cho, Yonggi Kim, Jiwon Park
Concept inventories in astronomy are typically organized around curriculum-defined content domains, on the implicit assumption that conceptual understanding partitions along those same lines. This assumption has rarely been examined empirically, in part because probing it requires an instrument both aligned with a specific curriculum and broad enough to capture cross-domain structure. We developed the Astronomy Curriculum-aligned Diagnostic Assessment (AcuDA), a 26-item instrument aligned with the 2022 revised Korean science curriculum and adapted from six established concept inventories, and administered it to 735 Korean university students (114 astronomy majors, 621 non-majors). AcuDA showed strong internal consistency (α = .844, ωtotal = .928). Factor analysis distinguished four content domains whose latent correlations ranged from .86 to .94. Given these high correlations, bifactor modeling, which separates a general factor from domain-specific factors, showed the general factor dominated (ωh= .895, ECV = .830). Cross-group invariance supported comparability between majors and non-majors, while distractor patterns revealed group-specific misconceptions on shared items. Because learner responses were organized primarily along a single latent dimension rather than four separable proficiencies, a single total score provides more interpretable and useful information than separate domain scores. Beyond providing the first astronomy concept inventory developed within and validated against the Korean national science curriculum, these results offer initial evidence that astronomy understanding may not partition cleanly along curriculum-defined content domains, and that its underlying cognitive architecture is better characterized as a shared reasoning dimension than as a set of separable domain abilities.
4,900원
8.
2026.07
구독 인증기관 무료, 개인회원 유료
Bogyeong Kim, Sung-Hong Park, Yu Yi
We investigate subsurface horizontal flow patterns beneath solar active regions (ARs) 12738 and 12673 down to a depth of 13 Mm. The analysis is based on time-distance helioseismology applied to photospheric line-of-sight velocity observations obtained by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). AR 12738 is a relatively simple and stable β-type AR, whereas AR 12673 evolved from an initially simple α-type region into a complex βγδ magnetic configuration through persistent and significant magnetic flux emergence. Despite their distinct magnetic evolution, both ARs exhibit similar depth-dependent subsurface flow patterns. In the shallow layers (0–3 Mm), converging flows are found beneath the umbral region identified from continuum intensity maps, whereas diverging flows dominate beneath the penumbral region. At depths of approximately 5 Mm, strong diverging flows dominate both within and surrounding the umbral region, and the divergence gradually decreases with depth. One notable difference between the two ARs is that the diverging flows below about 5 Mm beneath the umbral region extend to greater depths (up to about 13 Mm) in AR 12673 than in AR 12738. These findings suggest that the overall depth-dependent subsurface flow structure remains similar despite differences in photospheric magnetic complexity and magnetic evolution. The deeper diverging flows observed beneath the umbral region of AR 12673 may reflect a larger and more deeply rooted subsurface magnetic structure.
4,300원
9.
2026.07
구독 인증기관 무료, 개인회원 유료
Yuna Lee, Jongsuk Hong, Beomdu Lim
Open clusters are ideal observational testbeds for understanding the dynamics of stellar systems. We present a dynamical study of the young open cluster NGC 2302. The latest Gaia data and UBV IJHKs photometric data are used in this study. A total of 117 stars are selected as genuine members using the Gaia data. This cluster is, on average, reddened by ⟨E(B − V )⟩ = 0.24 ± 0.06 (s.d.). The ratio of total-to-selective extinction (RV ) in the direction of NGC 2302 is 2.8±0.1. The cluster distance is determined to be 1.16 ± 0.08 kpc using Gaia parallaxes. Theoretical isochrone fitting for Z = 0.008 on color-magnitude diagrams yields an age of 80 ± 20 Myr. The relative proper motions of individual members show no significant radial expansion or contraction. NGC 2302 contains a total stellar mass of 333±48M⊙. The one-dimensional velocity dispersion is approximately 0.26 kms−1, which is comparable to the virial velocity dispersion of 0.27 kms−1 derived from its total mass. Its relaxation time is estimated to be approximately 92 Myr, which is similar to the age of the cluster within the uncertainty in age estimation. Finally, we report a pattern of mass segregation in the radial distribution of stellar masses. Our results suggest that NGC 2302 is virialized and currently approaching a state of dynamical relaxation. However, because no definitive evidence of kinetic energy equipartition is found, the possibility of in-situ formation of high-mass stars within the central region should be carefully considered.
4,200원
