The application of data mining in astronomical surveys,such as the Large Sky Area MultiObject Fiber Spectroscopic Telescope(LAMOST)survey,provides an effective approach to automatically analyze a large amount of compl...The application of data mining in astronomical surveys,such as the Large Sky Area MultiObject Fiber Spectroscopic Telescope(LAMOST)survey,provides an effective approach to automatically analyze a large amount of complex survey data.Unsupervised clustering could help astronomers find the associations and outliers in a big data set.In this paper,we employ the k-means method to perform clustering for the line index of LAMOST spectra with the powerful software Astro Stat.Implementing the line index approach for analyzing astronomical spectra is an effective way to extract spectral features for low resolution spectra,which can represent the main spectral characteristics of stars.A total of 144 340 line indices for A type stars is analyzed through calculating their intra and inter distances between pairs of stars.For intra distance,we use the definition of Mahalanobis distance to explore the degree of clustering for each class,while for outlier detection,we define a local outlier factor for each spectrum.Astro Stat furnishes a set of visualization tools for illustrating the analysis results.Checking the spectra detected as outliers,we find that most of them are problematic data and only a few correspond to rare astronomical objects.We show two examples of these outliers,a spectrum with abnormal continuum and a spectrum with emission lines.Our work demonstrates that line index clustering is a good method for examining data quality and identifying rare objects.展开更多
The Taosi site in Xiangfen County,Shanxi Province,may be the capital of the King Yao. Archeologists recently discovered a large semi-circular stamped-earth platform, II FJT1,which has a clear and definite pounded-eart...The Taosi site in Xiangfen County,Shanxi Province,may be the capital of the King Yao. Archeologists recently discovered a large semi-circular stamped-earth platform, II FJT1,which has a clear and definite pounded-earth central core together with a curved wall perforated by twelve gaps. The platform is said to be an ancient observatory used to determine the seasons by watching the sunrise. Each feature of II FJT1 was precisely measured and the data are reproduced in this paper. An astronomical analysis of slots E2 and E12 was carried out using the azimuths of the slots' centerlines and the vertical angle of the mountain ridge opposite, above which the sun rises. The results show that at present the sun is close to the two slots but does not exactly enter them at summer and winter solstice sunrise. Using 14C analysis archeologists dated the site to about 2100 BC. Because of the secular change in the obliquity of the ecliptic,at that date on the summer solstice the half-risen sun would have appeared inside slot E12 just to the right of the centerline,and on the winter solstice the sun would have been exactly on the centerline of slot E2. This result provides compelling proof that II FJT1 is an ancient observatory.展开更多
在悬浮磁偶极场约束装置中,姿态控制系线圈(Tilt-Slide-Rotate,TSR)或者由高能量的粒子共振(Resonant Line Field,RLF)激发磁场会破坏背景磁场的拓扑结构,进而影响粒子约束。由于α粒子是DD-3He催化核反应产物之一,能否在TSR线圈和RLF...在悬浮磁偶极场约束装置中,姿态控制系线圈(Tilt-Slide-Rotate,TSR)或者由高能量的粒子共振(Resonant Line Field,RLF)激发磁场会破坏背景磁场的拓扑结构,进而影响粒子约束。由于α粒子是DD-3He催化核反应产物之一,能否在TSR线圈和RLF效应产生的磁场扰动中稳定约束高能量α粒子,对于加热背景等离子体的研究具有非常重要的意义。本研究中背景磁偶极场是通过偶极场平衡代码求解一个交换稳定的平衡得到的,在TSR线圈倾斜和偏移的工作模式下,对粒子投掷位置和TSR线圈工作电流α粒子约束时间和空间特性进行统计,同时在背景磁偶极场中叠加环向磁场方法模拟低极向扰动模数的磁场。由于TSR线圈产生磁场会破坏背景磁偶极场闭合磁场线的结构,使得投掷位置靠近TSR线圈侧的α粒子迅速损失。在RLF效应引发的模数n=0和n=1的极向扰动磁场中,在10μs内,n=0极向扰动磁场比n=1的磁扰动约束粒子份额更高,且当α粒子飞行时间大于10μs后,n=0模式下约束粒子份额迅速减少。展开更多
基金supported by the Joint Research Fund in Astronomy (U1631239) under cooperative agreement between the National Natural Science Foundation of China (NSFC) and Chinese Academy of Sciences (CAS)supported by the International Science and Technology Cooperation Program of China (2014DFE10030)the Basic Science and Engineering Special Project of Heilongjiang Province Education Department (135109219)
文摘The application of data mining in astronomical surveys,such as the Large Sky Area MultiObject Fiber Spectroscopic Telescope(LAMOST)survey,provides an effective approach to automatically analyze a large amount of complex survey data.Unsupervised clustering could help astronomers find the associations and outliers in a big data set.In this paper,we employ the k-means method to perform clustering for the line index of LAMOST spectra with the powerful software Astro Stat.Implementing the line index approach for analyzing astronomical spectra is an effective way to extract spectral features for low resolution spectra,which can represent the main spectral characteristics of stars.A total of 144 340 line indices for A type stars is analyzed through calculating their intra and inter distances between pairs of stars.For intra distance,we use the definition of Mahalanobis distance to explore the degree of clustering for each class,while for outlier detection,we define a local outlier factor for each spectrum.Astro Stat furnishes a set of visualization tools for illustrating the analysis results.Checking the spectra detected as outliers,we find that most of them are problematic data and only a few correspond to rare astronomical objects.We show two examples of these outliers,a spectrum with abnormal continuum and a spectrum with emission lines.Our work demonstrates that line index clustering is a good method for examining data quality and identifying rare objects.
文摘The Taosi site in Xiangfen County,Shanxi Province,may be the capital of the King Yao. Archeologists recently discovered a large semi-circular stamped-earth platform, II FJT1,which has a clear and definite pounded-earth central core together with a curved wall perforated by twelve gaps. The platform is said to be an ancient observatory used to determine the seasons by watching the sunrise. Each feature of II FJT1 was precisely measured and the data are reproduced in this paper. An astronomical analysis of slots E2 and E12 was carried out using the azimuths of the slots' centerlines and the vertical angle of the mountain ridge opposite, above which the sun rises. The results show that at present the sun is close to the two slots but does not exactly enter them at summer and winter solstice sunrise. Using 14C analysis archeologists dated the site to about 2100 BC. Because of the secular change in the obliquity of the ecliptic,at that date on the summer solstice the half-risen sun would have appeared inside slot E12 just to the right of the centerline,and on the winter solstice the sun would have been exactly on the centerline of slot E2. This result provides compelling proof that II FJT1 is an ancient observatory.
文摘在悬浮磁偶极场约束装置中,姿态控制系线圈(Tilt-Slide-Rotate,TSR)或者由高能量的粒子共振(Resonant Line Field,RLF)激发磁场会破坏背景磁场的拓扑结构,进而影响粒子约束。由于α粒子是DD-3He催化核反应产物之一,能否在TSR线圈和RLF效应产生的磁场扰动中稳定约束高能量α粒子,对于加热背景等离子体的研究具有非常重要的意义。本研究中背景磁偶极场是通过偶极场平衡代码求解一个交换稳定的平衡得到的,在TSR线圈倾斜和偏移的工作模式下,对粒子投掷位置和TSR线圈工作电流α粒子约束时间和空间特性进行统计,同时在背景磁偶极场中叠加环向磁场方法模拟低极向扰动模数的磁场。由于TSR线圈产生磁场会破坏背景磁偶极场闭合磁场线的结构,使得投掷位置靠近TSR线圈侧的α粒子迅速损失。在RLF效应引发的模数n=0和n=1的极向扰动磁场中,在10μs内,n=0极向扰动磁场比n=1的磁扰动约束粒子份额更高,且当α粒子飞行时间大于10μs后,n=0模式下约束粒子份额迅速减少。
