Pub Date : 2021-08-01DOI: 10.5303/JKAS.2021.54.4.121
Ki-beom Kim, Heon-Young Chang
{"title":"DO THE OBSERVED RELATIONS OF THE GLOBAL SEISMIC PARAMETERS DEPEND ON THE MAGNETIC ACTIVITY LEVEL","authors":"Ki-beom Kim, Heon-Young Chang","doi":"10.5303/JKAS.2021.54.4.121","DOIUrl":"https://doi.org/10.5303/JKAS.2021.54.4.121","url":null,"abstract":"","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45187731","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-08-01DOI: 10.5303/JKAS.2021.54.4.129
Ki-beom Kim, Heon-Young Chang
{"title":"TEMPORAL VARIATIONS OF THE GLOBAL SEISMIC PARAMETERS OF HD 49933 OVER A MAGNETIC CYCLE","authors":"Ki-beom Kim, Heon-Young Chang","doi":"10.5303/JKAS.2021.54.4.129","DOIUrl":"https://doi.org/10.5303/JKAS.2021.54.4.129","url":null,"abstract":"","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43788930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-06-16DOI: 10.5303/JKAS.2021.54.3.103
Hyesung Kang
The intracluster medium (ICM) is expected to experience on average about three passages of weak shocks with low sonic Mach numbers, M ≲ 3, during the formation of galaxy clusters. Both protons and electrons could be accelerated to become high energy cosmic rays (CRs) at such ICM shocks via diffusive shock acceleration (DSA). We examine the effects of DSA by multiple shocks on the spectrum of accelerated CRs by including in situ injection/acceleration at each shock, followed by repeated re-acceleration at successive shocks in the test-particle regime. For simplicity, the accelerated particles are assumed to undergo adiabatic decompression without energy loss and escape from the system, before they encounter subsequent shocks. We show that in general the CR spectrum is flattened by multiple shock passages, compared to a single episode of DSA, and that the acceleration efficiency increases with successive shock passages. However, the decompression due to the expansion of shocks into the cluster outskirts may reduce the amplification and flattening of the CR spectrum by multiple shock passages. The final CR spectrum behind the last shock is determined by the accumulated effects of repeated re-acceleration by all previous shocks, but it is relatively insensitive to the ordering of the shock Mach numbers. Thus multiple passages of shocks may cause the slope of the CR spectrum to deviate from the canonical DSA power-law slope of the current shock.
{"title":"Diffusive Shock Acceleration by Multiple Weak Shocks","authors":"Hyesung Kang","doi":"10.5303/JKAS.2021.54.3.103","DOIUrl":"https://doi.org/10.5303/JKAS.2021.54.3.103","url":null,"abstract":"The intracluster medium (ICM) is expected to experience on average about three passages of weak shocks with low sonic Mach numbers, M ≲ 3, during the formation of galaxy clusters. Both protons and electrons could be accelerated to become high energy cosmic rays (CRs) at such ICM shocks via diffusive shock acceleration (DSA). We examine the effects of DSA by multiple shocks on the spectrum of accelerated CRs by including in situ injection/acceleration at each shock, followed by repeated re-acceleration at successive shocks in the test-particle regime. For simplicity, the accelerated particles are assumed to undergo adiabatic decompression without energy loss and escape from the system, before they encounter subsequent shocks. We show that in general the CR spectrum is flattened by multiple shock passages, compared to a single episode of DSA, and that the acceleration efficiency increases with successive shock passages. However, the decompression due to the expansion of shocks into the cluster outskirts may reduce the amplification and flattening of the CR spectrum by multiple shock passages. The final CR spectrum behind the last shock is determined by the accumulated effects of repeated re-acceleration by all previous shocks, but it is relatively insensitive to the ordering of the shock Mach numbers. Thus multiple passages of shocks may cause the slope of the CR spectrum to deviate from the canonical DSA power-law slope of the current shock.","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70738622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-01DOI: 10.5303/JKAS.2021.54.2.71
Jeong-Sun Hwang, Changbom Park, Soo-hyeon Nam, Haeun Chung
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-planner galaxy-galaxy encounters and study the evolution of disk spins of interacting galaxies. Specifically, we consider the cases where the late-type target galaxy encounters an equally massive companion galaxy, which has either a late or an early-type morphology, with the 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 find 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 deflection 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 insufficient to increase the overall galactic spin under the conditions we set. It is found that the spin angular momentum of the target galaxy disk decreases by 15 - 20% after a prograde collision. We conclude that the accumulated effects of galaxy-galaxy interactions will play an important role in determining the total angular momentum of late-type galaxies at current stage.
{"title":"EVOLUTION OF THE SPIN OF LATE-TYPE GALAXIES CAUSED BY GALAXY-GALAXY INTERACTIONS","authors":"Jeong-Sun Hwang, Changbom Park, Soo-hyeon Nam, Haeun Chung","doi":"10.5303/JKAS.2021.54.2.71","DOIUrl":"https://doi.org/10.5303/JKAS.2021.54.2.71","url":null,"abstract":"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-planner galaxy-galaxy encounters and study the evolution of disk spins of interacting galaxies. Specifically, we consider the cases where the late-type target galaxy encounters an equally massive companion galaxy, which has either a late or an early-type morphology, with the 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 find 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 deflection 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 insufficient to increase the overall galactic spin under the conditions we set. It is found that the spin angular momentum of the target galaxy disk decreases by 15 - 20% after a prograde collision. We conclude that the accumulated effects of galaxy-galaxy interactions will play an important role in determining the total angular momentum of late-type galaxies at current stage.","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42086555","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-01DOI: 10.5303/JKAS.2021.54.2.49
Jae-Ok Lee, Kyoung-Sun Lee, J. Seough, Kyungsuk Cho
{"title":"Comparison of LOS Doppler Velocities and Non-thermal Line Widths in the Off-limb Solar Corona Measured Simultaneously by CoMP and Ninode/EIS","authors":"Jae-Ok Lee, Kyoung-Sun Lee, J. Seough, Kyungsuk Cho","doi":"10.5303/JKAS.2021.54.2.49","DOIUrl":"https://doi.org/10.5303/JKAS.2021.54.2.49","url":null,"abstract":"","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42135306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-01DOI: 10.5303/JKAS.2021.54.2.61
Jae-Ok Lee, Kyungsuk Cho, V. Nakariakov, Harim Lee, R. Kim, S. 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 find 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 km s − 1 . Among 19 blobs, 10 blobs have experienced at least two cycles of radial speed oscillations with different 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 fluid dynamic experiments. We find that the observed Strouhal numbers range from 0.2 to 2.1, consistent with those (0.15–3.0) from fluid dynamic experiments of bluff spheres, while they are higher than those (0.15–0.25) from MHD simulations of cylindrical shapes. We thus find that blobs formed in a post-CME CS undergo kinematic oscillations caused by fluid dynamic vortex shedding. The vortex shedding is driven by the interaction of the outward-moving blob having a bluff spherical shape with the background plasma in the post-CME CS.
{"title":"KINEMATIC OSCILLATIONS OF POST-CME BLOBS DETECTED BY K-COR ON 2017 SEPTEMBER 10","authors":"Jae-Ok Lee, Kyungsuk Cho, V. Nakariakov, Harim Lee, R. Kim, S. Jang, Heesu Yang, Sujin Kim, Yeon-Han Kim","doi":"10.5303/JKAS.2021.54.2.61","DOIUrl":"https://doi.org/10.5303/JKAS.2021.54.2.61","url":null,"abstract":": 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 find 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 km s − 1 . Among 19 blobs, 10 blobs have experienced at least two cycles of radial speed oscillations with different 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 fluid dynamic experiments. We find that the observed Strouhal numbers range from 0.2 to 2.1, consistent with those (0.15–3.0) from fluid dynamic experiments of bluff spheres, while they are higher than those (0.15–0.25) from MHD simulations of cylindrical shapes. We thus find that blobs formed in a post-CME CS undergo kinematic oscillations caused by fluid dynamic vortex shedding. The vortex shedding is driven by the interaction of the outward-moving blob having a bluff spherical shape with the background plasma in the post-CME CS.","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41780297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-02-01DOI: 10.5303/JKAS.2021.54.1.9
Nuri Park, E. Hwang, Yeonjung Kim, Yeongju Park, Deokhun Kang, Jonghoon Kim, I. Hong, G. Jo, Hosub Song, K. W. Min, Y. Yi
{"title":"Conceptual Structural Design and Comparative Power System Analysis of Ozone Dynamics Investigation Nano-satellite (ODIN)","authors":"Nuri Park, E. Hwang, Yeonjung Kim, Yeongju Park, Deokhun Kang, Jonghoon Kim, I. Hong, G. Jo, Hosub Song, K. W. Min, Y. Yi","doi":"10.5303/JKAS.2021.54.1.9","DOIUrl":"https://doi.org/10.5303/JKAS.2021.54.1.9","url":null,"abstract":"","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47797743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-02-01DOI: 10.5303/JKAS.2021.54.1.1
Minjun Kim, H. An
{"title":"X-RAY PROPERTIES OF THE PULSAR PSR J0205+6449 IN 3C 58","authors":"Minjun Kim, H. An","doi":"10.5303/JKAS.2021.54.1.1","DOIUrl":"https://doi.org/10.5303/JKAS.2021.54.1.1","url":null,"abstract":"","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48700212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.5303/JKAS.2021.54.3.89
M. Im, Yonggi Kim, Chung-Uk Lee, Hee-Won Lee, S. Pak, Hyunjin Shim, H. Sung, W. Kang, Taewoo Kim, Jeong-Eun Heo, T. Hinse, M. Ishiguro, G. Lim, Cuc T. K. Lý, G. S. Paek, Jinguk Seo, Joh-Na Yoon, J. Woo, Hojae Ahn, Hojin Cho, Changsu Choi, Jimin Han, Sungyong Hwang, Tae-Geun Ji, Seong-Kook Lee, Sumin Lee, Sunwoo Lee, Chang-Gone Kim, Dohoon Kim, Joonho Kim, S. Kim, M. Jeong, Bomi Park, I. Paek, Dohyeong Kim, Changbom Park
Even in an era where 8-meter class telescopes are common, small telescopes are considered very valuable research facilities since they are available for rapid follow-up or long term monitoring observations. To maximize the usefulness of small telescopes in Korea, we established the SomangNet, a network of 0.4-1.0 m class optical telescopes operated by Korean institutions, in 2020. Here, we give an overview of the project, describing the current participating telescopes, its scientific scope and operation mode, and the prospects for future activities. SomangNet currently includes 10 telescopes that are located in Australia, USA, and Chile as well as in Korea. The operation of many of these telescopes currently relies on operators, and we plan to upgrade them for remote or robotic operation. The latest SomangNet science projects include monitoring and follow-up observational studies of galaxies, supernovae, active galactic nuclei, symbiotic stars, solar system objects, neutrino/gravitational-wave sources, and exoplanets.
{"title":"Somangnet: Small Telescope Network of Korea","authors":"M. Im, Yonggi Kim, Chung-Uk Lee, Hee-Won Lee, S. Pak, Hyunjin Shim, H. Sung, W. Kang, Taewoo Kim, Jeong-Eun Heo, T. Hinse, M. Ishiguro, G. Lim, Cuc T. K. Lý, G. S. Paek, Jinguk Seo, Joh-Na Yoon, J. Woo, Hojae Ahn, Hojin Cho, Changsu Choi, Jimin Han, Sungyong Hwang, Tae-Geun Ji, Seong-Kook Lee, Sumin Lee, Sunwoo Lee, Chang-Gone Kim, Dohoon Kim, Joonho Kim, S. Kim, M. Jeong, Bomi Park, I. Paek, Dohyeong Kim, Changbom Park","doi":"10.5303/JKAS.2021.54.3.89","DOIUrl":"https://doi.org/10.5303/JKAS.2021.54.3.89","url":null,"abstract":"Even in an era where 8-meter class telescopes are common, small telescopes are considered very valuable research facilities since they are available for rapid follow-up or long term monitoring observations. To maximize the usefulness of small telescopes in Korea, we established the SomangNet, a network of 0.4-1.0 m class optical telescopes operated by Korean institutions, in 2020. Here, we give an overview of the project, describing the current participating telescopes, its scientific scope and operation mode, and the prospects for future activities. SomangNet currently includes 10 telescopes that are located in Australia, USA, and Chile as well as in Korea. The operation of many of these telescopes currently relies on operators, and we plan to upgrade them for remote or robotic operation. The latest SomangNet science projects include monitoring and follow-up observational studies of galaxies, supernovae, active galactic nuclei, symbiotic stars, solar system objects, neutrino/gravitational-wave sources, and exoplanets.","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70738848","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-01DOI: 10.5303/JKAS.2020.53.3.69
H. Barbier, E. Lopez, Bryan Tipan, C. Vásconez
{"title":"Sun Flux Variations due to Orbiting Planets: The Solar System as a Non-compact Planetary System","authors":"H. Barbier, E. Lopez, Bryan Tipan, C. Vásconez","doi":"10.5303/JKAS.2020.53.3.69","DOIUrl":"https://doi.org/10.5303/JKAS.2020.53.3.69","url":null,"abstract":"","PeriodicalId":49994,"journal":{"name":"Journal of the Korean Astronomical Society","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45719850","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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