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
제58권 제2호 (2025년 7월) 14건
1.
2025.07
구독 인증기관·개인회원 무료
2.
2025.07
구독 인증기관 무료, 개인회원 유료
We investigate the infrared variability of carbon stars in the Large Magellanic Cloud (LMC). Our sample consists of 11,134 carbon stars identified in both visual and infrared bands. Among these, 1,184 objects are known Mira variables based on the Optical Gravitational Lensing Experiment III (OGLE-III) observations. We study the infrared variability of the entire sample using the Wide-field Infrared Survey Explorer (WISE) photometric data spanning the past 16 years, including the AllWISE multiepoch data and the Near-Earth Object WISE Reactivation (NEOWISE-R) 2024 final data release. We generate light curves using WISE observations in the W1 and W2 bands and compute Lomb-Scargle periodograms for all sample stars. From the WISE light curves, we derive reliable variability parameters for 1,615 objects. Among these, we identify 672 objects exhibiting clear Mira-like variations: 445 of these are previously known Miras from OGLE-III, while 227 are candidates for new Mira variables identified from the WISE data. We establish period-magnitude and period-color relations in both visual and infrared bands for the known Miras and the newly identified candidates from WISE data. We anticipate that these relations will serve as valuable references for studying carbon stars in other galaxies, including the Milky Way.
4,500원
3.
2025.07
구독 인증기관 무료, 개인회원 유료
Atmospheric characterization has become a crucial area of study for exoplanets. The exoplanets known as ultra-hot Jupiters (UHJs) offer a natural laboratory for studying extreme atmospheric physics that cannot be observed in the solar system. One way to analyze their atmospheres is by transmission spectroscopy. However, it can be challenging to obtain such information because a planet’s signal is too weak compared to that of its host star, resulting in the planetary contribution to the observed spectrum being negligible. Therefore, the minimum observational requirements must be assessed first to distinguish the planetary signal from the stellar one to study these planets. In this context, we obtained the transmission spectra of UHJs TOI-1431 b and WASP-189 b by observing each exoplanet for one night with BOAO Echelle Spectrograph (BOES) on the 1.8 m telescope at Bohyunsan Optical Astronomy Observatory (BOAO). We searched for various chemical species by cross-correlating the exoplanetary spectra with model synthetic spectra. Our search for atmospheric signal returned a detection confidence level less than 3 σ for both targets. Therefore, we applied model injection to recover the atmospheric signals of the planets and assessed the minimum signal-to-noise ratio (S/N) to achieve 5 σ detection. During our search, we successfully recovered the planet signals with detection significances of 5.11 σ after a 750% injection of the model signal for TOI-1431 b and 5.02 σ for a 90% injection forWASP-189 b. These signal injection exercises suggest that a higher S/N of the transmission spectra is required to detect the planetary absorption features, and this can be done by stacking data from the observations of more than three cycles of the transit of a planet with a small-scale height such as WASP-189 b at BOAO facilities.
5,100원
4.
2025.07
구독 인증기관 무료, 개인회원 유료
Solar energetic particle (SEP) events, driven by solar flares and coronal mass ejections (CMEs), are occasionally accompanied by ground level enhancements (GLEs), detected by neutron monitors. While GLEs represent only a subset of SEP events, their occurrence may provide insight into the acceleration and propagation mechanisms of SEPs. In this study, we conducted a statistical analysis of 122 SEP events from 1997 to 2023, including 16 events associated with GLE and 106 without, using elemental composition data from the ACE/SIS instrument and X-ray fluence data from GOES/XRS. The results show that SEP events with GLE exhibit significantly higher fluences of SIS elements (He, C, N, O, Ne, Mg, Si) than those without, particularly at high energy channels. Notably, the fluences of carbon and oxygen were particularly enhanced in SEP events associated with GLE, suggesting a potential role for these elements in the generation of GLEs. A strong correlation (average r ≈ 0.75) was observed between the X-ray fluence of associated solar flares and the elemental fluences in SEP events with GLE, whereas a weaker correlation (average r ≈ 0.32–0.40) was found for SEP events without GLE. These findings imply that the presence of a GLE is linked to distinct acceleration conditions and enhanced ion production, particularly of light ions with large charge-to-mass ratios. This study contributes to a better understanding of SEP composition, GLE-associated mechanisms, and their relevance to space weather forecasting and radiation hazard assessments.
4,200원
5.
2025.07
구독 인증기관 무료, 개인회원 유료
Heesu Yang, Maria S. Madjarska, Donguk Song, Hannah Kwak, Sung-Hong Park, Eun-Kyung Lim, Sujin Kim, Su-Chan Bong, Yeon-Han Kim, Seonghwan Choi
The Challan instrument is a solar full-disk imaging spectroscopic telescope planned to be installed at three sites with a 120-degree longitudinal difference, enabling continuous 24-hour observations of the Sun. It will take data every 2.5 min with a spatial resolution of 2–3′′ and a spectral resolving power (R) of >43,000 in Hα and Ca ii 8542 Å bands simultaneously. Challan is composed of two modules, each dedicated to a specific waveband. This modular design is beneficial in minimizing the scattered light and simplifying the structure and engineering. The primary scientific goal of Challan is to investigate solar flares and filament eruptions. It is also expected to detect small-scale events in the solar chromosphere. In 2025, Challan will be installed at the Big Bear Solar Observatory for test observational runs, followed by scientific runs in 2026.
4,000원
6.
2025.07
구독 인증기관 무료, 개인회원 유료
We investigated three fan-shaped jets observed above sunspot light bridges or nearby sunspot regions. The study aimed to explore the dynamics and physical properties of jets’ features that appear as blob-like structures at the tips of the jets, which we call ‘dark blobs’. A transparent region is observed beneath the dark blobs, creating a visible gap between the dark blobs and the trailing body of the jets. These phenomena were studied in chromospheric and transition region imaging and spectral high-resolution co-observations from the Visible Imaging Spectrometer of the Goode Solar Telescope at the Big Bear Solar Observatory and the Interface Region Imaging Spectrograph (IRIS), together with data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We analyzed the jets’ morphology and fine structure. We obtained the spatial scale and the dynamics of the dark blobs that are seen mostly in the wings of the Hα line and have a cross-section of about 0.2′′–0.3′′. The dark blobs and the transparent regions are seen bright (in emission) in the IRIS slit-jaw 1330 Å, 1400 Å, and AIA 304 Å images. The IRIS Si iv 1394 Å spectrum of the brightenings showed blue-shifted emission of about 16 km s−1 with non-thermal velocities of up to 40 km s−1. We also estimated the electron density of the blue-shifted brightenings to be 1012.1±0.2 cm−3. Our findings likely suggest that we detect the observational signatures of shock waves that generate and/or contribute to the evolution of fan-shaped jets.
4,200원
7.
2025.07
구독 인증기관 무료, 개인회원 유료
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.
4,200원
8.
2025.07
구독 인증기관 무료, 개인회원 유료
Young stellar objects (YSOs) can display unpredictable and high-amplitude rises in brightness that can last from a few months to possibly over 100 years. These types of outbursts are explained by large changes in the mass accretion rate from the disk onto the central star. This type of variability has given support to a model of star formation (episodic accretion) where stars would spend most of their lifetimes accreting at low rates, and gain most of their mass through these short-lived accretion outbursts. The universality of episodic accretion, as well as its potential impact on stellar and planetary formation are still under debate. Improvement on the statistics of the members of the eruptive class is needed to better understand the episodic accretion phenomenon and its universality across different mass regimes and environments. In this paper we collect published information on the spectroscopic and photometric characteristics of 174 YSOs confirmed to belong to the eruptive variable class. We classify these objects into five different sub-classes (we find 49 FUor, 20 FUor-like, 16 EX Lupi-type, 81 Peculiar/V1647 Ori-like/MNors and 8 Periodic YSOs). The classification follows what has been done previously in the literature, and it is not an attempt to redefine these classes. In addition, we present a list of 18 embedded, and 6 massive YSOs, as additional categories of eruptive variable YSOs. Due to the complexity and/or faintness of these systems, it is hard to place them into the original classification scheme of this class of variable YSOs. Finally, we present a separate list of 355 candidate eruptive variable YSOs, which either lack spectroscopic information or the available spectroscopic data is not sufficient for an unambiguous classification. The online catalogue of confirmed and candidate eruptive YSOs will be maintained and updated in the future to serve as an important reference for the star formation community.
5,800원
9.
2025.07
구독 인증기관 무료, 개인회원 유료
Time-domain statistical studies of mid-infrared and submm variability in nearby star-forming regions show that at least half of all protostars are variable. In this study, we present a statistical analysis of the mid-infrared variability of Young Stellar Objects (YSOs) in the distant, massive star-forming region W51, based on data from the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) All-Sky Survey. From a catalog of 81 protostars, 527 disk objects, and 37,687 other sources, including diskless pre-main sequence stars (Class III) and likely evolved contaminants such as AGB stars (collectively labeled as PMS+E), we identified significant variability in both the 3.4 μm(W1) and 4.6 μm(W2) bands. Due to the large distance (∼5.4 kpc) and high extinction of W51, our sample primarily includes intermediate- to high-mass YSOs (≥2 M⊙), in contrast to nearby star-forming regions such as Taurus or the Gould Belt, which are dominated by low-mass stars (≤1M⊙). This mass bias may affect the observed variability characteristics and their interpretation. Specifically, 11.1% of protostars, 7.6% of Disk objects, and 0.6% of PMS+E sources exhibited secular variability in the W2, while 8.6% of protostars, 2.3% of Disk objects, and 0.5% of PMS+E sources exhibited stochastic variability. Similar trends were observed in the W1 band. Both the fraction and amplitude of variability increase toward earlier evolutionary stages. Protostars exhibit predominantly stochastic variability with high amplitudes, likely driven by dynamic accretion, and extinction changes. In contrast, disk objects show more secular variability, including linear, curved, and periodic patterns, possibly caused by moderate accretion changes or geometric modulation in the inner disk. Analysis of brightness and color changes revealed that protostars typically become redder as they brighten, while disk objects show more complex behavior: they appear roughly balanced in W1 but more often become bluer in W2. These trends are consistent with enhanced dust emission or extinction in protostars, and reduced extinction or accretion-induced hotspot modulation in disk objects. These trends reflect the distinct physical mechanisms at play across evolutionary stages and demonstrate that mid-infrared variability provides useful insight into the accretion and disk evolution processes in young stars.
4,300원
10.
2025.07
구독 인증기관 무료, 개인회원 유료
Tracing the water snowline in low-mass young stellar objects (YSOs) is important because dust grain growth is promoted and the chemical composition varies at the water snowline, which influences planet formation and its properties. In protostellar envelopes, the water snowline can be estimated as a function of luminosity using a relation derived from radiative transfer models, and these predictions are consistent with observations. However, accurately estimating the water snowline in protoplanetary disks requires new relations that account for the disk structure. We present the relations between luminosity and water snowline using the dust continuum radiative transfer models with various density structures. We adopt two-dimensional density structures for an envelope-only model (Model E), an envelope+disk+cavity model (Model E+D), and a protoplanetary disk model (Model PPD). The relations between the water snowline, where Tdust = 100 K, and the total luminosity, ranging 0.1–1,000 L⊙, are well fitted by a power-law relation, Rsnow = a × (L/L⊙)p au. The factor a decreases with increasing disk density, while the power index p has values around 0.5 in all models. As the disk becomes denser, the water snowline forms at smaller radii even at the same luminosity, since dense dust hinders photon propagation. We also explore the effect of viscous heating on the water snowline. In Model PPD with viscous heating, the water snowline shifts outward by a few au up to 15 au, increasing the factor a and decreasing the power index p. In Model E+D with lower disk mass, the effect of viscous heating is negligible, indicating that the disk mass controls the effect. The discrepancy between our models and direct observations provides insights into the recent outburst event and the presence of a disk structure in low-mass YSOs.
4,300원
11.
2025.07
구독 인증기관 무료, 개인회원 유료
Recent advances in millimeter- and submillimeter-wave astronomy demand heterodyne receivers that simultaneously provide wide intermediate-frequency (IF) bandwidth and low receiver noise temperature. In this work, we present the design, fabrication, and experimental validation of a wide-IF (8–16 GHz) superconductor-insulator-superconductor (SIS) mixer for the 150 GHz band. The device employs a series array of four Nb/AlOx/Nb SIS junctions with a target RF embedding impedance near the optimum impedance of 31 Ω, and it is integrated with a pentagonal probe and a WR 6.5 waveguide for RF broadband coupling. Full-circuit simulations conducted in SuperMix were used to define the layout, and the performance of the fabricated mixer was evaluated in a 4 K test cryogenic receiver using hot/cold-load measurements over the 8–16 GHz IF band in double-sideband (DSB) mode. At a local oscillator (LO) frequency of 154 GHz, the mixer exhibits a maximum DSB conversion gain of 6 dB with a corresponding receiver noise temperature (Trx) ∼ 29 K. Across the IF band, Trx averages 43 K with a range of 25–76 K. These results establish the developed mixer as a promising candidate for next-generation wide-IF astronomical receivers.
4,000원
12.
2025.07
구독 인증기관 무료, 개인회원 유료
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.
4,900원
13.
2025.07
구독 인증기관 무료, 개인회원 유료
The wide-angle Polarimetric Camera (PolCam) onboard South Korea’s first lunar orbiter, Danuri, is a pioneering instrument designed to conduct the first global polarimetric and high-phase-angle survey of the Moon. Precise geometric calibration is critical for this mission, particularly due to PolCam’s highly oblique viewing geometry, which introduces significant topographic distortion. We present a comprehensive on-orbit geometric calibration that relies on 160,256 tie points derived from matching features between PolCam images and the well-orthorectified global map of the Kaguya Multiband Imager (MI). This dataset allows us to address two fundamental challenges: (1) the accurate reconstruction of the observation time for each line of an observation strip via a simple linear model, and (2) the refinement of the precise camera model, geometric model for PolCam optics. Our optimization method for these two challenges transforms the 2D image coordinates of identified features into 3D lunar coordinates and minimizes the reprojection error against the reference coordinates provided by the Kaguya MI map. From the refined observation time and camera model, we compute the precise longitude, latitude, and elevation of each pixel of an observed image. These estimated 3D coordinates are then used to generate orthorectified images, the final product of the geometric calibration. The resulting calibration achieves a geometric precision comparable to that of previous lunar orbiters and establishes the foundational framework necessary to produce geometrically-corrected data products of PolCam.
4,500원
14.
2025.07
구독 인증기관 무료, 개인회원 유료
This paper is intended to demonstrate how to apply an inversion method to one of the observed solar active regions (ARs) generally having complex magnetic structure. The method was developed in our previous work for solving an inverse problem to derive physical properties of a subsurface magnetic field from surface magnetic field evolution. We handled two key issues in the application of the method to the observed AR, one of which is to reconstruct three-dimensional magnetic structure of the AR, while the other is to select a single magnetic flux tube responsible for an X-class flare observed in this AR by isolating closed magnetic-loop structure from the reconstructed AR structure. The isolation of the loop structure is essential for a proper evaluation of unsigned magnetic flux and relative magnetic helicity, which are used to solve the inverse problem. By refining data of the so-called force-free α, we also derived the principal field line representing the axis of the selected flux tube in the AR, which could contribute to a quantitative classification of ARs having full of variety in size, magnetic field strength, and magnetic field configuration.
4,000원
