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Investigation of Umbral Dots with the New Vacuum Solar Telescope  

Song Feng   Submitted: 2015-09-29 04:50

Umbral dots (UDs) are small isolated brightenings observed in sunspot umbrae. They are convective phenomena existing inside umbrae. UDs are usually divided into central UDs (CUDs) and peripheral UDs (PUDs) according to their positions inside an umbra. Our purpose is to investigate UD properties and analyze their relationships, and further to find whether or not the properties depend on the umbral magnetic field variation. For this purpose, we selected the high-resolution TiO images of four active regions (ARs) obtained under the best seeing conditions with the New Vacuum Solar Telescope in the Fuxian Solar Observatory of the Yunnan Astronomical Observatory, China. The four ARs (NOAA 11598, 11801, 12158, and 12178) include six sunspots. A total of 1220 CUDs were identified in six sunspots, and 603 PUDs in three sunspots. Meanwhile, the radial component of the magnetic field of the sunspots obtained with the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory was used to analyze the relationship between UD properties and the magnetic field. The diameters and lifetimes of CUDs exhibit an increasing trend with brightness, whereas their horizontal velocities exhibit an inverse trend. Moreover, the diameter, intensity and velocity depend on the magnetic field variation. The diameter of a CUD becomes larger and brighter, and its motion slower in a weak magnetic field than in a strong field. Similar trends are also found for PUDs. Moreover, we also find that the lifetimes of UDs located in different sunspots are not obviously different, implying that they are unrelated to the magnetic flux density in which they live.

Authors: Kaifan Ji, Xia Jiang, Song Feng, Yunfei Yang, Hui Deng, Feng Wang
Projects: None

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2015-09-29 13:05
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Investigation of Umbral Dots with the New Vacuum Solar Telescope

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