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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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1
- Tetsuya Magara
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.2
- pp.305-313
- 2025
- 원문 바로보기
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.
2
- Kyung-Won Suh
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.2
- pp.131-143
- 2025
- 원문 바로보기
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.
3
- Daeil Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.1
- pp.55-61
- 2025
- 원문 바로보기
In this study, we examine the relationships between the National Oceanic and Atmospheric Administration (NOAA) space weather scale frequencies and the maximum monthly sunspot number in each solar cycle: 1975 to 2020 for radio blackouts (R scales) and solar radiation storms (S scales), 1932 to 2020 for geomagnetic storms (G scales). Our main results are as follows. First, we find that NOAA space weather scale frequencies have strong solar cycle dependencies. Second, we propose new linear relationships between the frequency of certain scales (R1 to R4, and G1 to G4) and the maximum monthly sunspot number. T-test results show that R1 to R3 and G1 to G4 relationships are statistically meaningful, but marginal for R4. Third, our results significantly reduce the root-mean-square error (RMSE) between observed and suggested frequencies compared to the NOAA's current frequencies. For example, in the case of solar cycle 24, our new prediction (74) for R3 scale is much more consistent with the observational frequency (74) than the NOAA prediction (175), and our prediction (85) for G3 scale is much closer to the observation (40) than the NOAA prediction (200). Our work may provide a useful guideline for advancing the space weather scales.
4
- Gu Lim
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.1
- pp.31-42
- 2025
- 원문 바로보기
We present optical observations of a nearby Type Ia supernova (SN Ia) 2018kp on January 24 2018, +1.4 days after the estimated first light time. Its host galaxy, NGC 3367, has been under high-cadence monitoring (≲1 day) with the purpose of providing valuable early light curves of supernovae as a primary target of the Intensive Monitoring Survey of Nearby Galaxies (IMSNG; Im et al. 2019). SN 2018kp exhibits the characteristics of a normal SN Ia, with a peak luminosity of M<sub>B</sub> = -19.0 ± 0.4 mag and Δm<sub>15</sub>(B) = 1.19 ± 0.03 mag, derived from our long-term light curve analysis. We estimate the host extinction to be high [E(B - V )<sub>host</sub> = 0.697 ± 0.028 mag], contrasting with its sibling, SN 1986A. We estimate the mass of <sup>56</sup>Ni synthesized in the explosion to be M<sub>Ni</sub> = 0.55±0.14 M<sub>⊙</sub>. A single power-law model (t<sup>α</sup>) describes the rising behavior of the early light curve well, with little evidence of the shock-heated cooling emission. We place upper limits on the radii of the progenitor (R<sub>p</sub> ≤ 1.8 R<sub>⊙</sub>) and the companion star (R<sub>c</sub> ≤ 1.9 R<sub>⊙</sub> at the optimal or R<sub>c</sub> ≤ 19.2 R<sub>⊙</sub> at the common viewing angle, respectively) ruling out a large companion such as a red giant. Based on our data, we derive a distance to the host galaxy of 41.38 ± 2.20 Mpc assuming that SN 2018kp follows the Phillips relation.
5
- Heon-Young Chang
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.2
- pp.281-290
- 2025
- 원문 바로보기
In this study, we have studied properties of solar, interplanetary, and geomagnetic indices for the period from 1976 to 2024 in view of active days and spotless days. Specifically, we have compared the characteristics of monthly spotless days in percent around a solar minimum period for each solar cycle. In addition, we have revisited the slope of the linear relationship between monthly mean sunspot numbers and monthly number of active days and further explored similar relationship with the F10.7 index, solar flare index, mean magnetic field of the Sun, Kp, Ap, Dst, AE indices, as well as the magnitude of interplanetary magnetic field with components of the interplanetary magnetic field. As a result, we have found that the distribution of monthly number of spotless days has a skewed shape in common, yet varies from one solar cycle to another implying that the number of spotless days around the solar minimum can be used as a predictor of the maximum level of solar activity. It is also found that the slope of the linear relationship in solar parameters tends to become steeper as the maximum sunspot number is large. Unlike solar parameters, results from interplanetary and geomagnetic indices reveal a quite dissimilar behavior. We conclude that the study in terms of active (spotless) days assures combination of various solar and interplanetary indices is required to find a more geoeffective parameter.
6
- Jaeyeong Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.1
- pp.111-129
- 2025
- 원문 바로보기
We present the combined 2.5-30 ㎛ spectra of four protostars acquired with the infrared camera and the infrared spectrograph on board the AKARI and Spitzer space telescopes, respectively. To analyze the ice absorption features in the 8-22 ㎛, we first performed a continuum determination process on mid-infrared spectra and applied a method to subtract the silicate absorption. We conducted a global fitting process to the absorption features in the combined infrared spectra using the experimental ice absorbance data to identify the intrinsic absorption of each ice component. We first derived the H<sub>2</sub>O ice column densities of both stretch and libration modes at 3.05 ㎛ and 13.6 ㎛ simultaneously. We also identified the absorption features containing NH<sub>3</sub>, CH<sub>3</sub>OH, CO<sub>2</sub>, and CO and decomposed their mixed components and compared their ice abundances at different evolutionary stages of the protostars. We explored possible absorptions of the organic ice species such as HCOOH, CH<sub>3</sub>CHO, and CH<sub>3</sub>CH<sub>2</sub>OH in the mid-infrared ranges. The ice analysis method developed in this study can be applied to the ice spectra obtained by the James Webb Space Telescope.
7
- Carlos Contreras Pena
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.2
- pp.209-230
- 2025
- 원문 바로보기
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.
8
- Kilho Baek
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.2
- pp.291-303
- 2025
- 원문 바로보기
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.
9
- Heesu Yang
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.2
- pp.185-195
- 2025
- 원문 바로보기
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<sup>-1</sup> with non-thermal velocities of up to 40 km s<sup>-1</sup>. We also estimated the electron density of the blue-shifted brightenings to be 1012.1±0.2 cm<sup>-3</sup>. 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.
10
- Juhyung Kang
- Journal of the Korean Astronomical Society = 천문학회지
- 58, n.1
- pp.63-70
- 2025
- 원문 바로보기
The Fast Imaging Solar Spectrograph (FISS) is a powerful instrument for studying photospheric and chromospheric events by simultaneously recording high-resolution spectrograms in two spectral bands. Recently, because of a change in the optical setup, unexpected fringes have been noticed on the Ca ii 8542 Å band camera, which persist even after the standard flat-fielding. Here, we develop a new data calibration method for the FISS, including a wavelet-based fringe reduction technique. By applying the wavelet transform independently along each axis of the flat data, we successfully isolate the fringes using a low-pass filter and a Gaussian window in the power spectrum. We implement the phase correction to account for temporal phase shifts in the fringes, enabling their effective removal from object frames without altering spectral profiles. This preprocessing pipeline has been integrated into the Python-based FISSpy package for the FISS data analysis. We anticipate that the proposed calibration method will enhance data quality and be utilized for the next generation of the FISS.