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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
페이지 4/123
31
- 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.
32
- 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.
33
- 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.
34
- Dohyeong Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.95-103
- 2024
- 원문 바로보기
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.
35
- Changmin Kim
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.11-11
- 2024
- 원문 바로보기
The following sentence was erroneously dropped from the acknowledgment: This work was supported by Chungnam National University. The corrected text is listed below; it should replace the Acknowledgements section.
36
- Yong-Jae Moon
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.35-44
- 2024
- 원문 바로보기
The Sun-Earth Lagrange point L4, which is called a parking space of space, is considered one of the unique places where solar activity and the heliospheric environment can be observed continuously and comprehensively. The L4 mission affords a clear and wide-angle view of the Sun-Earth line for the study of Sun-Earth connections from remote-sensing observations. The L4 mission will significantly contribute to advancing heliophysics science, improving space weather forecasting capability, extending space weather studies far beyond near-Earth space, and reducing risk from solar radiation hazards on human missions to the Moon and Mars. Our paper outlines the importance of L4 observations by using remote-sensing instruments and advocates comprehensive and coordinated observations of the heliosphere at multi-points including other planned L1 and L5 missions. We mainly discuss scientific perspectives on three topics in view of remote sensing observations: (1) solar magnetic field structure and evolution, (2) source regions of geoeffective solar energetic particles (SEPs), and (3) stereoscopic views of solar corona and coronal mass ejections (CMEs).
37
- Sanghyeon Han
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.249-259
- 2024
- 원문 바로보기
We examine whether the radial acceleration relation (RAR) of dwarf galaxies can be explained by Verlinde's emergent gravity. This is the extension of Yoon et al. (2023), which examine the RAR of typical spiral galaxies, to less massive systems. To do this, we compile the line-of-sight velocity dispersion profiles of 30 dwarf galaxies in the Local Group from the literature. We then calculate the expected gravitational acceleration from the stellar component in the framework of the emergent gravity, and compare it with that from observations. The calculated acceleration with the emergent gravity under the assumption of a quasi-de Sitter universe agrees with the observed one within the uncertainty. Our results suggest that the emergent gravity can explain the kinematics of galaxies without introducing dark matter, even for less massive galaxies where dark matter is expected to dominate. This sharply contrasts with MOND, where a new interpolating function has to be introduced for dwarf galaxies to explain their kinematics without dark matter.
38
- Kim Dachan
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.1
- pp.45-54
- 2024
- 원문 바로보기
The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) will provide all-sky spectral survey data covering optical to mid-infrared wavelengths with a spatial resolution of 6.'2, which can be widely used to study galaxy formation and evolution. We investigate the galaxy-galaxy blending in SPHEREx datasets using the mock galaxy catalogs generated from cosmological simulations and observational data. Only ~0.7% of the galaxies will be blended with other galaxies in all-sky survey data with a limiting magnitude of 19 AB mag. However, the fraction of blended galaxies dramatically increases to ~7-9% in the deep survey area around the ecliptic poles, where the depth reaches ~22 AB mag. We examine the impact of the blending in the number count and luminosity function analyses using the SPHEREx data. We find that the number count can be overestimated by up to 10-20% in the deep regions due to the flux boosting, suggesting that the impact of galaxy-galaxy blending on the number count is moderate. However, galaxy-galaxy blending can marginally change the luminosity function by up to 50% over a wide range of redshifts. As we only employ the magnitude limit at K<sub>s</sub>-band for the source detection, the blending fractions determined in this study should be regarded as lower limits.
39
- Kyung-Won Suh
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.123-134
- 2024
- 원문 바로보기
We investigate the properties of AGB and post-AGB (PAGB) stars, planetary nebulae, and young stellar objects (YSOs) in our Galaxy through an analysis of observational data covering visual and infrared (IR) wavelengths. Utilizing datasets from IRAS, 2MASS, AllWISE, Gaia DR3, and the SIMBAD object database, we perform an in-depth comparison between observational data and theoretical models. For this comparison, we present various color-magnitude diagrams (CMDs) in visual and IR bands, as well as IR two-color diagrams (2CDs). Our results demonstrate that the CMDs, incorporating the latest distance and extinction data from Gaia DR3 for a majority of sample stars, are effective in distinguishing different classes of stars. To improve the precision of our analysis, we apply theoretical radiative transfer models for dust shells around AGB and PAGB stars. A thorough comparison of the theoretical models with observations across various IR 2CDs and CMDs shows a significant agreement. We find that AGB and PAGB stars are among the brightest classes in visual and IR bands. Furthermore, most YSOs are clearly distinguishable from AGB stars on various IR CMDs, exhibiting fainter absolute magnitudes in IR bands.
40
- So-Myoung Park
- Journal of the Korean Astronomical Society = 천문학회지
- 57, n.2
- pp.211-221
- 2024
- 원문 바로보기
We investigate the evolution of initial fractal clusters at 3 kpc from the Galactic Center (GC) of the Milky Way and show how red supergiant clusters (RSGCs)-like objects, which are considered to be the result of active star formation in the Scutum complex, can form by 16 Myr. We find that initial tidal filling and tidal over-filling fractals are shredded by the tidal force, but some substructures can survive as individual subclusters, especially when the initial virial ratio is ≤0.5. These surviving subclusters are weakly mass segregated and show a top-heavy mass function. This implies the possibility that a single substructured star cluster can evolve into multiple 'star clusters'.