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 ~ 2024
- 주제분류 자연과학 > 천문학 자연과학 분류의 다른 간행물
- 십진분류KDC 440DDC 520
권호리스트/논문검색
제54권 제2호 (2021년 4월) 4건
1.
2021.04
구독 인증기관 무료, 개인회원 유료
Minjin Kim, Woong-Seob Jeong, Yujin Yang, Jiwon Son, Luis C. Ho, Jong-Hak Woo, Myungshin Im, Woowon Byun
Reverberation mapping (RM) is an ecient method to investigate the physical sizes of the broad line region (BLR) and dusty torus in an active galactic nucleus (AGN). The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission will provide multi-epoch spectroscopic data at optical and near-infrared wavelengths. These data can be used for RM experiments with bright AGNs. We present results of a feasibility test using SPHEREx data in the SPHEREx deep regions for torus RM measurements. We investigate the physical properties of bright AGNs in the SPHEREx deep eld. Based on this information, we compute the eciency of detecting torus time lags in simulated light curves. We demonstrate that, in combination with complementary optical data with a depth of 20 mag in Bband, lags of 750 days for tori can be measured for more than 200 bright AGNs. If high signal-to-noise ratio photometric data with a depth of 21{22 mag are available, RM measurements are possible for up to 900 objects. When complemented by well-designed early optical observations, SPHEREx can provide a unique dataset for studies of the physical properties of dusty tori in bright AGNs.
4,200원
2.
2021.04
구독 인증기관 무료, 개인회원 유료
Observations of line of sight (LOS) Doppler velocity and non-thermal line width in the o -limb solar corona are often used for investigating the Alfven wave signatures in the corona. In this study, we compare LOS Doppler velocities and non-thermal line widths obtained simultaneously from two di erent instruments, Coronal Multichannel Polarimeter (CoMP) and Hinode/EUV Imaging Spectrometer (EIS), on various o -limb coronal regions: aring and quiescent active regions, equatorial quiet region, and polar prominence and plume regions observed in 2012{2014. CoMP provides the polarization at the Fe xiii 10747 A coronal forbidden lines which allows their spectral line intensity, LOS Doppler velocity, and line width to be measured with a low spectral resolution of 1.2 A in 2-D o limb corona between 1.05 and 1.40 RSun, while Hinode/EIS gives us the EUV spectral information with a high spectral resolution (0.025 A) in a limited eld of view raster scan. In order to compare them, we make pseudo raster scan CoMP maps using information of each EIS scan slit time and position. We compare the CoMP and EIS spectroscopic maps by visual inspection, and examine their pixel to pixel correlations and percentages of pixel numbers satisfying the condition that the di erences between CoMP and EIS spectroscopic quantities are within the EIS measurement accuracy: 3 kms1 for LOS Doppler velocity and 9 kms1 for non-thermal width. The main results are summarized as follows. By comparing CoMP and EIS Doppler velocity distributions, we nd that they are consistent with each other overall in the active regions and equatorial quiet region (0.25 CC 0.7), while they are partially similar to each other in the overlying loops of prominences and near the bottom of the polar plume (0.02 CC 0.18). CoMP Doppler velocities are consistent with the EIS ones within the EIS measurement accuracy in most regions ( 87% of pixels) except for the polar region (45% of pixels). We nd that CoMP and EIS non-thermal width distributions are similar overall in the active regions (0.06 CC 0.61), while they seem to be di erent in the others (0:1 CC 0.00). CoMP non-thermal widths are similar to EIS ones within the EIS measurement accuracy in a quiescent active region (79% of pixels), while they do not match in the other regions ( 61% of pixels); the CoMP observations tend to underestimate the widths by about 20% to 40% compared to the EIS ones. Our results demonstrate that CoMP observations can provide reliable 2-D LOS Doppler velocity distributions on active regions and might provide their non-thermal width distributions.
4,300원
3.
2021.04
구독 인증기관 무료, 개인회원 유료
Jae-Ok Lee, Kyung-Suk Cho, Valery M. Nakariakov, Harim Lee, Rok-Soon Kim, Soojeong Jang, Heesu Yang, Sujin Kim, Yeon-Han Kim
We investigate 20 post-coronal mass ejection (CME) blobs formed in the post-CME current sheet (CS) that were observed by K-Cor on 2017 September 10. By visual inspection of the trajectories and projected speed variations of each blob, we nd that all blobs except one show irregular \zigzag" trajectories resembling transverse oscillatory motions along the CS, and have at least one oscillatory pattern in their instantaneous radial speeds. Their oscillation periods are ranging from 30 to 91 s and their speed amplitudes from 128 to 902 kms1. Among 19 blobs, 10 blobs have experienced at least two cycles of radial speed oscillations with di erent speed amplitudes and periods, while 9 blobs undergo one oscillation cycle. To examine whether or not the apparent speed oscillations can be explained by vortex shedding, we estimate the quantitative parameter of vortex shedding, the Strouhal number, by using the observed lateral widths, linear speeds, and oscillation periods of the blobs. We then compare our estimates with theoretical and experimental results from MHD simulations and uid dynamic experiments. We nd that the observed Strouhal numbers range from 0.2 to 2.1, consistent with those (0.15{3.0) from uid dynamic experiments of blu spheres, while they are higher than those (0.15{0.25) from MHD simulations of cylindrical shapes. We thus nd that blobs formed in a post-CME CS undergo kinematic oscillations caused by uid dynamic vortex shedding. The vortex shedding is driven by the interaction of the outward-moving blob having a blu spherical shape with the background plasma in the post-CME CS.
4,000원
4.
2021.04
구독 인증기관 무료, 개인회원 유료
We use N-body/hydrodynamic simulations to study the evolution of the spin of a Milky Way-like galaxy through interactions. We perform a controlled experiment of co-planar galaxy-galaxy encounters and study the evolution of disk spins of interacting galaxies. Speci cally, we consider cases where the late-type target galaxy encounters an equally massive companion galaxy, which has either a late or an early-type morphology, with a closest approach distance of about 50 kpc, in prograde or retrograde sense. By examining the time change of the circular velocity of the disk material of the target galaxy from each case, we nd that the target galaxy tends to lose the spin through prograde collisions but hardly through retrograde collisions, regardless of the companion galaxy type. The decrease of the spin results mainly from the de ection of the orbit of the disk material by tidal disruption. Although there is some disk material which gains the circular velocity through hydrodynamic as well as gravitational interactions or by transferring material from the companion galaxy, it turns out that the amount of the material is generally insucient to increase the overall galactic spin under the conditions we set. We nd that the spin angular momentum of the target galaxy disk decreases by 15{20% after a prograde collision. We conclude that the accumulated e ects of galaxy-galaxy interactions will play an important role in determining the total angular momentum of late-type galaxies.
5,200원
