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Characterizing motion types of G-band bright points in the quiet sun

Research in Astronomy and Astrophysics 2015年第4期15卷 569-582页

作者： Yun-Fei Yang Hui-Xue Qu Kai-Fan Ji Song Feng Hui Deng Jia-Ben Lin Feng Wang Faculty of Information Engineering and Automation / Yunnan Key Laboratory of Computer Technology Application Kunming University of Science and Technology Key Laboratory of Solar Activity National Astronomical ObservatoriesChinese Academy of Sciences Key Laboratory of Modern Astronomy and Astrophysics Nanjing UniversityMinistry of Education Yunnan Observatories Chinese Academy of Sciences

We study the motion of G-band bright points （GBPs） in the quiet sun to obtain the characteristics of different motion types. A high resolution image sequence taken with the Hinode/Solar Optical Telescope （SOT） is used, and GBPs are automat- ically tracked by segmenting 3D evolutional structures in a space-time cube. After putting the GBPs that do not move during their lifetimes aside, the non-stationary GBPs are categorized into three types based on an index of their motion type. Most GBPs that move in straight or nearly straight lines are categorized as a straight mo- tion type, a few moving in rotary paths into rotary motion, and the others fall into a motion type we called erratic. The mean horizontal velocities are 2.18±0.08 km s-1, 1.63±0.09km s^-1 and 1.33±0.07 km s^-1 for straight, erratic and rotary motion types, respectively. We find that a GBP drifts at a higher and constant velocity during its whole life if it moves in a straight line. However, it has a lower and variational velocity if it moves on a rotary path. The diffusive process is ballistic-, super- and sub-diffusion for straight, erratic and rotary motion types, respectively. The corresponding diffusion index （γ） and coefficients （K） are 2.13±0.09 and 850±37km^2 s^-1, 1.82±0.07 and 331 ±24 km^2 s^-1, and 0.73±0.19 and 13±9 km^2 s^-1. In terms of direction of motion, it is homogeneous and isotropic, and usually persists between neighboring frames, no matter what motion type a GBP is classified as.

关键词： techniques： image processing -- sun： photosphere -- methods： dataanalysis -- methods： statistical

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Evolution of isolated G-band bright points: size, intensity and velocity

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Research in Astronomy and Astrophysics 2014年第6期14卷 741-752页

作者： Yun-Fei Yang Jia-Ben Lin Song Feng Kai-Fan Ji Hui Deng Feng Wang Faculty of Information Engineering and Automation/Yunnan Key Laboratory of Computer Technology Application Kunming University of Science and Technology Key Laboratory of Solar Activity National Astronomical Observatories Chinese Academy of Sciences Key Laboratory of Modern Astronomy and Astrophysics Nanjing University Ministry of Education

We study the evolution pattern of isolated G-band bright points （GBPs） in terms of their size, intensity and velocity. Using a high resolution image sequence taken with the Hinode/Solar Optical Telescope （SOT）, we detect GBPs in each image by the Laplacian and Morphological Dilation algorithm, and track their evolutions by a 26-adjacent method in a three-dimensional space-time cube. For quantifying the evolution, we propose a quantification method based on lifetime normalization which aligns the different lifetimes to common stages. The quantification results show that, on average, the diameter of isolated GBPs changes from 166 to 173 km, then down to 165 km; the maximum intensity contrast changes from 1.012 to 1.027, then down to 1.011; however, the velocity changes from 1.709 to 1.593 km s-1, then up to 1.703 km s-i. The results indicate that the evolution follows a pattern such that the GBP is small, faint and fast-moving at the birth stage, becomes big, bright and slow-moving at the middle stage, then gets small, faint and fast-moving at the decay stage until disappearance. Although the differences are very small, a two-sample t-test is used to demonstrate there are significant differences in means between the distri- butions of the different stages. Furthermore, we quantify the relationship between the lifetimes of GBPs and their properties. It is found that there are positive correlations between the lifetimes and their sizes and intensities with correlation coefficients of 0.83 and 0.65, respectively; however, there is a negative correlation between the life- times and velocities with a correlation coefficient of-0.49. In summary, the longer the GBP persists, the bigger, brighter and slower it will be.

关键词： techniques： image processing -- sun： photosphere -- methods： dataanalysis -- methods： statistical

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