Application of an Improved Method of Image Segmentation and Some Considerations on Identification and Tracking of Umbral Dots |
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| Authors: | H Hamedivafa |
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| Institution: | (1) Physics Department, Faculty of Science, Imam Khomeini International University, Qazvin, 34149-16818, Islamic Republic of Iran |
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| Abstract: | An improved method of image segmentation is introduced. The object-tracking algorithm, originally developed by Sobotka, Brandt,
and Simon (Astron. Astrophys. 328, 682, 1997) is modified with special attentions on splitting and merging of umbral dots (UDs), definition of the umbral boundary, and
the birth-frames and the death-frames of UDs. By applying the new method of image segmentation and the object-tracking algorithm
on a 67-min series of white-light images of a large pore (Sobotka et al., Astrophys. J.
511, 436, 1999), the physical characteristics of 20 “resolved” UDs with umbral origin were recorded. The most probable lifetime of the UDs
is between 7 and 10 min. Umbral dots show a typical size of about 230 km. Their mean speeds are smaller than 2 km s−1 with a distribution around a value less than 1 km s−1. However, their average velocities are less than 0.8 km s−1. Brighter (fainter) UDs are formed in the brighter (dimmer) region of the pore. There is no correlation between time-averaged
area or time-averaged speeds and lifetimes. Also, the time-averaged peak intensities of UDs do not show any well-defined dependence
on the corresponding time-averaged areas. It seems that there is a relation between average velocities of UDs and their time-averaged
peak intensities, with brighter UDs moving more slowly. |
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| Keywords: | Sunspots Umbra |
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