Investigation of Umbral Dots with the New Vacuum Solar Telescope

TL;DR

This study investigates the properties of umbral dots in sunspots using high-resolution images and magnetic field data, revealing how their characteristics depend on magnetic field strength.

Contribution

It provides new insights into how umbral dot properties vary with magnetic field strength and distinguishes differences between central and peripheral UDs.

Findings

UD diameters and lifetimes increase with brightness

UD velocities are unaffected by brightness

UD properties depend on surrounding magnetic field strength

Abstract

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 umbral magnetic field strengths. Thus, we selected high-resolution TiO images of four active regions (ARs) taken under the best seeing conditions with the \textit{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 and 603 PUDs were identified. Meanwhile, the radial component of the vector magnetic field of the sunspots taken with the \textit{Helioseismic and Magnetic Imager} on-board the \textit{Solar Dynamics Observatory} was used to analyze relationships between UD properties and umbral magnetic field strengths. We find that diameters and lifetimes of UDs exhibit an increasing trend with the brightness, but velocities do not. Moreover, diameters, intensities, lifetimes and velocities depend on the surrounding magnetic field. A CUD diameter was found larger, the CUD brighter, its lifetime longer, and its motion slower in a weak umbral magnetic field environment than in a strong one.