Identifying and Tracking of Peripheral and Central Umbral Dots

Abstract

Umbral dots (UDs) are small isolated brightening observed in sunspot umbrae. They are usually classified into peripheral UDs (PUDs) and central UDs (CUDs) according to their positions inside an umbra. To accurately investigate the similarities and the distinctions between PUDs and CUDs and better understand their formation mechanisms, we propose a method for identifying and tracking PUDs and CUDs. Firstly, the umbra–penumbra boundary was detected based on morphological reconstruction. Secondly, the UDs were identified and tracked based on phase congruency. Finally, the UDs were classified into PUDs and CUDs with a new definition of the periphery and the center of an umbra. A data set obtained with the Hinode/Solar Optical Telescope on 2 March 2007 was used to illustrate the procedures. The statistical properties of PUDs and CUDs, including equivalent diameters, ratio of the maximum intensity to the mean photosphere intensity, horizontal velocities, lifetimes, and trajectories were investigated to evaluate the performance of the method.