Pub Date : 2020-02-24DOI: 10.5140/JASS.2021.38.1.39
Uicheol Jang, Hongsu Kim, Y. Yi
In the general accretion disk model theory, the accretion disk surrounding an astronomical object comprises fluid rings obeying Keplerian motion. However, we should consider relativistic and rotational effects as we close in toward the center of accretion disk surrounding spinning compact massive objects such as a black hole or a neutron star. In this study, we explore the geometry of the inner portion of the accretion disk in the context of Mukhopadhyay’s pseudo-Newtonian potential approximation for the full general relativity theory. We found that the shape of the accretion disk “puffs up” or becomes thicker and the luminosity of the disk could exceed the Eddington luminosity near the surface of the compact spinning black hole.
{"title":"Thick Accretion Disk and Its Super Eddington Luminosity around a Spinning Black\u0000 Hole","authors":"Uicheol Jang, Hongsu Kim, Y. Yi","doi":"10.5140/JASS.2021.38.1.39","DOIUrl":"https://doi.org/10.5140/JASS.2021.38.1.39","url":null,"abstract":"In the general accretion disk model theory, the accretion disk surrounding an\u0000 astronomical object comprises fluid rings obeying Keplerian motion. However, we should\u0000 consider relativistic and rotational effects as we close in toward the center of\u0000 accretion disk surrounding spinning compact massive objects such as a black hole or a\u0000 neutron star. In this study, we explore the geometry of the inner portion of the\u0000 accretion disk in the context of Mukhopadhyay’s pseudo-Newtonian potential approximation\u0000 for the full general relativity theory. We found that the shape of the accretion disk\u0000 “puffs up” or becomes thicker and the luminosity of the disk could exceed the Eddington\u0000 luminosity near the surface of the compact spinning black hole.","PeriodicalId":44366,"journal":{"name":"Journal of Astronomy and Space Sciences","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2020-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84697369","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.5140/JASS.2019.36.4.283
Dong-Heun Kim, Yonggi Kim, Joh-Na Yoon, Hong-Seo Im
The purpose of this study was to develop a period analysis algorithm for detecting new variable stars in the time-series data observed by charge coupled device (CCD). We used the data from a variable star monitoring program of the CBNUO. The R filter data of some magnetic cataclysmic variables observed for more than 20 days were chosen to achieve good statistical results. World Coordinate System (WCS) Tools was used to correct the rotation of the observed images and assign the same IDs to the stars included in the analyzed areas. The developed algorithm was applied to the data of DO Dra, TT Ari, RXSJ1803, and MU Cam. In these fields, we found 13 variable stars, five of which were new variable stars not previously reported. Our period analysis algorithm were tested in the case of observation data mixed with various fields of view because the observations were carried with 2K CCD as well as 4K CCD at the CBNUO. Our results show that variable stars can be detected using our algorithm even with observational data for which the field of view has changed. Our algorithm is useful to detect new variable stars and analyze them based on existing time-series data. The developed algorithm can play an important role as a recycling technique for used data
{"title":"Development of a Period Analysis Algorithm for Detecting Variable Stars in\u0000 Time-Series Observational Data","authors":"Dong-Heun Kim, Yonggi Kim, Joh-Na Yoon, Hong-Seo Im","doi":"10.5140/JASS.2019.36.4.283","DOIUrl":"https://doi.org/10.5140/JASS.2019.36.4.283","url":null,"abstract":"The purpose of this study was to develop a period analysis algorithm for\u0000 detecting new variable stars in the time-series data observed by charge coupled device\u0000 (CCD). We used the data from a variable star monitoring program of the CBNUO. The R\u0000 filter data of some magnetic cataclysmic variables observed for more than 20 days were\u0000 chosen to achieve good statistical results. World Coordinate System (WCS) Tools was used\u0000 to correct the rotation of the observed images and assign the same IDs to the stars\u0000 included in the analyzed areas. The developed algorithm was applied to the data of DO\u0000 Dra, TT Ari, RXSJ1803, and MU Cam. In these fields, we found 13 variable stars, five of\u0000 which were new variable stars not previously reported. Our period analysis algorithm\u0000 were tested in the case of observation data mixed with various fields of view because\u0000 the observations were carried with 2K CCD as well as 4K CCD at the CBNUO. Our results\u0000 show that variable stars can be detected using our algorithm even with observational\u0000 data for which the field of view has changed. Our algorithm is useful to detect new\u0000 variable stars and analyze them based on existing time-series data. The developed\u0000 algorithm can play an important role as a recycling technique for used data","PeriodicalId":44366,"journal":{"name":"Journal of Astronomy and Space Sciences","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82746483","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.5140/JASS.2019.36.4.225
Heon-Young Chang
We explore the associations between the total sunspot area, solar north-south asymmetry, and Southern Oscillation Index and the physical characteristics of clouds by calculating normalized cross-correlations, motivated by the idea that the galactic cosmic ray influx modulated by solar activity may cause changes in cloud coverage, and in turn the Earth’s climate. Unlike previous studies based on the relative difference, we have employed cloud data as a whole time-series without detrending. We found that the coverage of high-level and low-level cloud is at a maximum when the solar north-south asymmetry is close to the minimum, and one or two years after the solar north-south asymmetry is at a maximum, respectively. The global surface air temperature is at a maximum five years after the solar north-south asymmetry is at a maximum, and the optical depth is at a minimum when the solar north-south asymmetry is at a maximum. We also found that during the descending period of solar activity, the coverage of low-level cloud is at a maximum, and global surface air temperature and cloud optical depth are at a minimum, and that the total column water vapor is at a maximum one or two years after the solar maximum.
{"title":"Normalized Cross-Correlations of Solar Cycle and Physical Characteristics of\u0000 Cloud","authors":"Heon-Young Chang","doi":"10.5140/JASS.2019.36.4.225","DOIUrl":"https://doi.org/10.5140/JASS.2019.36.4.225","url":null,"abstract":"We explore the associations between the total sunspot area, solar north-south\u0000 asymmetry, and Southern Oscillation Index and the physical characteristics of clouds by\u0000 calculating normalized cross-correlations, motivated by the idea that the galactic\u0000 cosmic ray influx modulated by solar activity may cause changes in cloud coverage, and\u0000 in turn the Earth’s climate. Unlike previous studies based on the relative difference,\u0000 we have employed cloud data as a whole time-series without detrending. We found that the\u0000 coverage of high-level and low-level cloud is at a maximum when the solar north-south\u0000 asymmetry is close to the minimum, and one or two years after the solar north-south\u0000 asymmetry is at a maximum, respectively. The global surface air temperature is at a\u0000 maximum five years after the solar north-south asymmetry is at a maximum, and the\u0000 optical depth is at a minimum when the solar north-south asymmetry is at a maximum. We\u0000 also found that during the descending period of solar activity, the coverage of\u0000 low-level cloud is at a maximum, and global surface air temperature and cloud optical\u0000 depth are at a minimum, and that the total column water vapor is at a maximum one or two\u0000 years after the solar maximum.","PeriodicalId":44366,"journal":{"name":"Journal of Astronomy and Space Sciences","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81957213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.5140/JASS.2019.36.4.235
Youngro Lee, Sang-Young Park, Jae-Pil Park, Youngbum Song
This paper suggests a relative orbit control strategy for the CubeSat Astronomy by NASA and Yonsei using Virtual Telescope Alignment eXperiment (CANYVAL-X) mission whose main goal is to demonstrate an essential technique, which is an arrangement among two satellites and a specific celestial object, referred to as inertial alignment, for a next-generation virtual space telescope. The inertial alignment system is a relative orbit control system and has requirements for the relative state. Through the proposed orbit control strategy, consisting of separation, proximity keeping, and reconfiguration, the requirements will be satisfied. The separation direction of the two CubeSats with respect to the orbital plane is decided to provide advantageous initial condition to the orbit controller. Proximity keeping is accomplished by differential atmospheric drag control (DADC), which generates acceleration by changing the spacecraft’s effective cross section via attitude control rather than consuming propellant. Reconfiguration is performed to meet the requirements after proximity keeping. Numerical simulations show that the requirements can be satisfied by the relative orbit control strategy. Furthermore, through numerical simulations, it is demonstrated that the inertial alignment can be achieved. A beacon signal had been received for several months after the launch; however, we have lost the signal at present.
{"title":"Numerical Analysis of Relative Orbit Control Strategy for CANYVAL-X Mission","authors":"Youngro Lee, Sang-Young Park, Jae-Pil Park, Youngbum Song","doi":"10.5140/JASS.2019.36.4.235","DOIUrl":"https://doi.org/10.5140/JASS.2019.36.4.235","url":null,"abstract":"This paper suggests a relative orbit control strategy for the CubeSat Astronomy\u0000 by NASA and Yonsei using Virtual Telescope Alignment eXperiment (CANYVAL-X) mission\u0000 whose main goal is to demonstrate an essential technique, which is an arrangement among\u0000 two satellites and a specific celestial object, referred to as inertial alignment, for a\u0000 next-generation virtual space telescope. The inertial alignment system is a relative\u0000 orbit control system and has requirements for the relative state. Through the proposed\u0000 orbit control strategy, consisting of separation, proximity keeping, and\u0000 reconfiguration, the requirements will be satisfied. The separation direction of the two\u0000 CubeSats with respect to the orbital plane is decided to provide advantageous initial\u0000 condition to the orbit controller. Proximity keeping is accomplished by differential\u0000 atmospheric drag control (DADC), which generates acceleration by changing the\u0000 spacecraft’s effective cross section via attitude control rather than consuming\u0000 propellant. Reconfiguration is performed to meet the requirements after proximity\u0000 keeping. Numerical simulations show that the requirements can be satisfied by the\u0000 relative orbit control strategy. Furthermore, through numerical simulations, it is\u0000 demonstrated that the inertial alignment can be achieved. A beacon signal had been\u0000 received for several months after the launch; however, we have lost the signal at\u0000 present.","PeriodicalId":44366,"journal":{"name":"Journal of Astronomy and Space Sciences","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88635575","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.5140/JASS.2019.36.4.293
Young-Rok Kim, Young-Joo Song
In this study, the observational arc-length effect on orbit determination (OD) for the Korea Pathfinder Lunar Orbiter (KPLO) in the Earth-Moon Transfer phase was investigated. For the OD, we employed a sequential estimation using the extended Kalman filter and a fixed-point smoother. The mission periods, comprised between the perigee maneuvers (PM) and the lunar orbit insertion (LOI) maneuver in a 3.5 phasing loop of the KPLO, was the primary target. The total period was divided into three phases: launch–PM1, PM1–PM3, and PM3–LOI. The Doppler and range data obtained from three tracking stations [included in the deep space network (DSN) and Korea Deep Space Antenna (KDSA)] were utilized for the OD. Six arc-length cases (24 hrs, 48 hrs, 60 hrs, 3 days, 4 days, and 5 days) were considered for the arc-length effect investigation. In order to evaluate the OD accuracy, we analyzed the position uncertainties, the precision of orbit overlaps, and the position differences between true and estimated trajectories. The maximum performance of 3-day OD approach was observed in the case of stable flight dynamics operations and robust navigation capability. This study provides a guideline for the flight dynamics operations of the KPLO in the trans-lunar phase.
{"title":"Observational Arc-Length Effect on Orbit Determination for Korea Pathfinder Lunar\u0000 Orbiter in the Earth-Moon Transfer Phase Using a Sequential Estimation","authors":"Young-Rok Kim, Young-Joo Song","doi":"10.5140/JASS.2019.36.4.293","DOIUrl":"https://doi.org/10.5140/JASS.2019.36.4.293","url":null,"abstract":"In this study, the observational arc-length effect on orbit determination (OD)\u0000 for the Korea Pathfinder Lunar Orbiter (KPLO) in the Earth-Moon Transfer phase was\u0000 investigated. For the OD, we employed a sequential estimation using the extended Kalman\u0000 filter and a fixed-point smoother. The mission periods, comprised between the perigee\u0000 maneuvers (PM) and the lunar orbit insertion (LOI) maneuver in a 3.5 phasing loop of the\u0000 KPLO, was the primary target. The total period was divided into three phases:\u0000 launch–PM1, PM1–PM3, and PM3–LOI. The Doppler and range data obtained from three\u0000 tracking stations [included in the deep space network (DSN) and Korea Deep Space Antenna\u0000 (KDSA)] were utilized for the OD. Six arc-length cases (24 hrs, 48 hrs, 60 hrs, 3 days,\u0000 4 days, and 5 days) were considered for the arc-length effect investigation. In order to\u0000 evaluate the OD accuracy, we analyzed the position uncertainties, the precision of orbit\u0000 overlaps, and the position differences between true and estimated trajectories. The\u0000 maximum performance of 3-day OD approach was observed in the case of stable flight\u0000 dynamics operations and robust navigation capability. This study provides a guideline\u0000 for the flight dynamics operations of the KPLO in the trans-lunar phase.","PeriodicalId":44366,"journal":{"name":"Journal of Astronomy and Space Sciences","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82746727","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.5140/jass.2019.36.4.249
Hyewon Hwang, Eunji Lee, Sang-Young Park
In this study, the precise orbit determination (POD) software is developed for optical observation. To improve the performance of the estimation algorithm, a nonlinear batch filter, based on the unscented transform (UT) that overcomes the disadvantages of the least-squares (LS) batch filter, is utilized. The LS and UT batch filter algorithms are verified through numerical simulation analysis using artificial optical measurements. We use the real optical observation data of a low Earth orbit (LEO) satellite, Cryosat-2, observed from optical wide-field patrol network (OWL-Net), to verify the performance of the POD software developed. The effects of light travel time, annual aberration, and diurnal aberration are considered as error models to correct OWL-Net data. As a result of POD, measurement residual and estimated state vector of the LS batch filter converge to the local minimum when the initial orbit error is large or the initial covariance matrix is smaller than the initial error level. However, UT batch filter converges to the global minimum, irrespective of the initial orbit error and the initial covariance matrix.
{"title":"Precise Orbit Determination Based on the Unscented Transform for Optical\u0000 Observations","authors":"Hyewon Hwang, Eunji Lee, Sang-Young Park","doi":"10.5140/jass.2019.36.4.249","DOIUrl":"https://doi.org/10.5140/jass.2019.36.4.249","url":null,"abstract":"In this study, the precise orbit determination (POD) software is developed for\u0000 optical observation. To improve the performance of the estimation algorithm, a nonlinear\u0000 batch filter, based on the unscented transform (UT) that overcomes the disadvantages of\u0000 the least-squares (LS) batch filter, is utilized. The LS and UT batch filter algorithms\u0000 are verified through numerical simulation analysis using artificial optical\u0000 measurements. We use the real optical observation data of a low Earth orbit (LEO)\u0000 satellite, Cryosat-2, observed from optical wide-field patrol network (OWL-Net), to\u0000 verify the performance of the POD software developed. The effects of light travel time,\u0000 annual aberration, and diurnal aberration are considered as error models to correct\u0000 OWL-Net data. As a result of POD, measurement residual and estimated state vector of the\u0000 LS batch filter converge to the local minimum when the initial orbit error is large or\u0000 the initial covariance matrix is smaller than the initial error level. However, UT batch\u0000 filter converges to the global minimum, irrespective of the initial orbit error and the\u0000 initial covariance matrix.","PeriodicalId":44366,"journal":{"name":"Journal of Astronomy and Space Sciences","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85310468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.5140/JASS.2019.36.4.265
Chun-Hwey Kim, Mi-Hwa Song, Jang-Ho Park, M. Jeong, Hye-Young Kim, C. Han
We present new BVRI light curves of UY UMa with no O’Connell effect and a flat bottom secondary eclipse. Light curve synthesis with the Wilson-Devinney code gives a new solution, which is quite different from the previous study: UY UMa is an A-subtype over-contact binary with a small mass ratio of q = 0.21, a high inclination of 81°.4, a small temperature difference of ΔT = 18°, a large fill-out factor of f = 0.61, and a third light of approximately 10% of the total systemic light. The absolute dimensions were newly determined. Seventeen new times of minimum light have been calculated from our observations. The period study indicates that the orbital period has intricately varied in a secular period increase in which two cyclical terms with periods of 12y.0 and 46y.3 are superposed. The secular period increase was interpreted to be due to a conservative mass transfer of 2.68 × 10–8 M⊙/yr from the less massive to the more massive star. The cyclical components are discussed in terms of double-light time contributions from two additional bound stars. The statistical relations of Yang & Qian (2015) among the physical parameters of 45 deep, low mass ratio contact binaries were revisited by using the physical parameters of UY UMa and 25 Kepler contact binaries provided by Şenavci et al. (2016).
{"title":"UY Ursae Majoris: An A-Subtype W UMa System with a Very Large Fill-Out Factor and\u0000 an Extreme Mass Ratio","authors":"Chun-Hwey Kim, Mi-Hwa Song, Jang-Ho Park, M. Jeong, Hye-Young Kim, C. Han","doi":"10.5140/JASS.2019.36.4.265","DOIUrl":"https://doi.org/10.5140/JASS.2019.36.4.265","url":null,"abstract":"We present new BVRI light curves of UY UMa with no O’Connell effect and a flat\u0000 bottom secondary eclipse. Light curve synthesis with the Wilson-Devinney code gives a\u0000 new solution, which is quite different from the previous study: UY UMa is an A-subtype\u0000 over-contact binary with a small mass ratio of q = 0.21, a high inclination of 81°.4, a\u0000 small temperature difference of ΔT = 18°, a large fill-out factor of f = 0.61, and a\u0000 third light of approximately 10% of the total systemic light. The absolute dimensions\u0000 were newly determined. Seventeen new times of minimum light have been calculated from\u0000 our observations. The period study indicates that the orbital period has intricately\u0000 varied in a secular period increase in which two cyclical terms with periods of 12y.0\u0000 and 46y.3 are superposed. The secular period increase was interpreted to be due to a\u0000 conservative mass transfer of 2.68 × 10–8 M⊙/yr from the less massive to the more\u0000 massive star. The cyclical components are discussed in terms of double-light time\u0000 contributions from two additional bound stars. The statistical relations of Yang &\u0000 Qian (2015) among the physical parameters of 45 deep, low mass ratio contact binaries\u0000 were revisited by using the physical parameters of UY UMa and 25 Kepler contact binaries\u0000 provided by Şenavci et al. (2016).","PeriodicalId":44366,"journal":{"name":"Journal of Astronomy and Space Sciences","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75548331","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-01DOI: 10.5140/JASS.2019.36.3.149
Jung-Hee Kim, Heon-Young Chang
In this study, we investigate the associations between the solar variability and teleconnection indices, which influence atmospheric circulation and subsequently, the spatial distribution of the global pressure system. A study of the link between the Sun and a large-scale mode of climate variability, which may indirectly affect the Earth’s climate and weather, is crucial because the feedbacks of solar variability to an autogenic or internal process should be considered with due care. We have calculated the normalized cross-correlations of the total sunspot area, the total sunspot number, and the solar North–South asymmetry with teleconnection indices. We have found that the Southern Oscillation Index (SOI) index is anti-correlated with both solar activity and the solar North–South asymmetry, with a ∼3-year lag. This finding not only agrees with the fact that El Niño episodes are likely to occur around the solar maximum, but also explains why tropical cyclones occurring in the solar maximum periods and in El Niño periods appear similar. Conversely, other teleconnection indices, such as the Arctic Oscillation (AO) index, the Antarctic Oscillation (AAO) index, and the Pacific-North American (PNA) index, are weakly or only slightly correlated with solar activity, which emphasizes that response of terrestrial climate and weather to solar variability are local in space. It is also found that correlations between teleconnection indices and solar activity are as good as correlations resulting from the teleconnection indices themselves.
{"title":"Association between Solar Variability and Teleconnection Index","authors":"Jung-Hee Kim, Heon-Young Chang","doi":"10.5140/JASS.2019.36.3.149","DOIUrl":"https://doi.org/10.5140/JASS.2019.36.3.149","url":null,"abstract":"In this study, we investigate the associations between the solar variability and\u0000 teleconnection indices, which influence atmospheric circulation and subsequently, the\u0000 spatial distribution of the global pressure system. A study of the link between the Sun\u0000 and a large-scale mode of climate variability, which may indirectly affect the Earth’s\u0000 climate and weather, is crucial because the feedbacks of solar variability to an\u0000 autogenic or internal process should be considered with due care. We have calculated the\u0000 normalized cross-correlations of the total sunspot area, the total sunspot number, and\u0000 the solar North–South asymmetry with teleconnection indices. We have found that the\u0000 Southern Oscillation Index (SOI) index is anti-correlated with both solar activity and\u0000 the solar North–South asymmetry, with a ∼3-year lag. This finding not only agrees with\u0000 the fact that El Niño episodes are likely to occur around the solar maximum, but also\u0000 explains why tropical cyclones occurring in the solar maximum periods and in El Niño\u0000 periods appear similar. Conversely, other teleconnection indices, such as the Arctic\u0000 Oscillation (AO) index, the Antarctic Oscillation (AAO) index, and the Pacific-North\u0000 American (PNA) index, are weakly or only slightly correlated with solar activity, which\u0000 emphasizes that response of terrestrial climate and weather to solar variability are\u0000 local in space. It is also found that correlations between teleconnection indices and\u0000 solar activity are as good as correlations resulting from the teleconnection indices\u0000 themselves.","PeriodicalId":44366,"journal":{"name":"Journal of Astronomy and Space Sciences","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84488349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-01DOI: 10.5140/jass.2019.36.3.133
Adero Ochieng Awuor, P. Baki, J. Olwendo, P. Kotzé
Challenging Minisatellite Payload (CHAMP) satellite magnetic data are used to investigate the latitudinal variation of the storm-time meso-scale field-aligned currents by defining a new metric called the FAC range. Three major geomagnetic storm events are considered. Alongside SymH, the possible contributions from solar wind dynamic pressure and interplanetary magnetic field (IMF) BZ are also investigated. The results show that the new metric predicts the latitudinal variation of FACs better than previous studies. As expected, the equatorward expansion and poleward retreat are observed during the storm main phase and recovery phase respectively. The equatorward shift is prominent on the northern duskside, at ~58° coinciding with the minimum SymH and dayside at ~59° compared to dawnside and nightside respectively. The latitudinal shift of FAC range is better correlated to IMF BZ in northern hemisphere dusk-dawn magnetic local time (MLT) sectors than in southern hemisphere. The FAC range latitudinal shifts responds better to dynamic pressure in the duskside northern hemisphere and dawnside southern hemisphere than in southern hemisphere dusk sector and northern hemisphere dawn sector respectively. FAC range exhibits a good correlation with dynamic pressure in the dayside (nightside) southern (northern) hemispheres depicting possible electrodynamic similarity at day-night MLT sectors in the opposite hemispheres.
{"title":"Storm-Time Behaviour of Meso-Scale Field-Aligned Currents: Case Study with Three\u0000 Geomagnetic Storm Events","authors":"Adero Ochieng Awuor, P. Baki, J. Olwendo, P. Kotzé","doi":"10.5140/jass.2019.36.3.133","DOIUrl":"https://doi.org/10.5140/jass.2019.36.3.133","url":null,"abstract":"Challenging Minisatellite Payload (CHAMP) satellite magnetic data are used to\u0000 investigate the latitudinal variation of the storm-time meso-scale field-aligned\u0000 currents by defining a new metric called the FAC range. Three major geomagnetic storm\u0000 events are considered. Alongside SymH, the possible contributions from solar wind\u0000 dynamic pressure and interplanetary magnetic field (IMF) BZ are also investigated. The\u0000 results show that the new metric predicts the latitudinal variation of FACs better than\u0000 previous studies. As expected, the equatorward expansion and poleward retreat are\u0000 observed during the storm main phase and recovery phase respectively. The equatorward\u0000 shift is prominent on the northern duskside, at ~58° coinciding with the minimum SymH\u0000 and dayside at ~59° compared to dawnside and nightside respectively. The latitudinal\u0000 shift of FAC range is better correlated to IMF BZ in northern hemisphere dusk-dawn\u0000 magnetic local time (MLT) sectors than in southern hemisphere. The FAC range latitudinal\u0000 shifts responds better to dynamic pressure in the duskside northern hemisphere and\u0000 dawnside southern hemisphere than in southern hemisphere dusk sector and northern\u0000 hemisphere dawn sector respectively. FAC range exhibits a good correlation with dynamic\u0000 pressure in the dayside (nightside) southern (northern) hemispheres depicting possible\u0000 electrodynamic similarity at day-night MLT sectors in the opposite hemispheres.\u0000","PeriodicalId":44366,"journal":{"name":"Journal of Astronomy and Space Sciences","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78324058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-01DOI: 10.5140/JASS.2019.36.3.105
Yeuncheol Jeong, A. Yushchenko, V. Gopka, V. Yushchenko, P. Rittipruk, K. S. Jeong, A. Demessinova
Spectroscopic observations of barium star ζ Capricornus (HD204075) obtained at the 8.2 m telescope of the European Southern Observatory, with a spectral resolving power R = 80,000 and signal to noise ratio greater than 300, were used to refine the atmospheric parameters. We found new values for effective temperature (Teff = 5,300 ± 50 K), surface gravity (log g = 1.82 ± 0.15), micro-turbulent velocity (vmicro = 2.52 ± 0.10 km/s), and iron abundance (log N (Fe) = 7.32 ± 0.06). Previously published abundances of chemical elements in the atmosphere of HD204075 were analyzed and no correlations of these abundances with the second ionization potentials of these elements were found. This excludes the possible influence of accretion of hydrogen and helium atoms from the interstellar or circumstellar environment to the atmosphere of this star. The accretion of nuclear processed matter from the evolved binary companion was primary cause of the abundance anomalies. The young age of HD204075 allows an estimation of the time-scale for the creation of the abundance anomalies arising from accretion of interstellar hydrogen and helium as is the case of stars with low magnetic fields; which we estimate should exceed 108 years.
利用欧洲南方天文台8.2 m望远镜获得的光谱分辨率R = 80000，信噪比大于300的钡星ζ Capricornus (HD204075)的光谱观测资料，对大气参数进行了细化。我们发现了有效温度(Teff = 5300±50 K)、地表重力(log g = 1.82±0.15)、微湍流速度(vmicro = 2.52±0.10 km/s)和铁丰度(log N (Fe) = 7.32±0.06)的新值。对HD204075大气中已公布的化学元素丰度进行了分析，发现这些元素的丰度与这些元素的二次电离势没有相关性。这排除了星际或星周环境中氢和氦原子的吸积对这颗恒星大气的可能影响。演化双星伴星的核加工物质的吸积是丰度异常的主要原因。HD204075的年轻年龄使得我们可以估计出由星际氢和氦的吸积引起的丰度异常产生的时间尺度，就像低磁场恒星的情况一样;我们估计应该超过108年。
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