Brightness, distribution, and evolution of sunspot umbral dots

Abstract

We present a 106-minute TiO (705.7nm) time series of high spatial and temporal resolution that contains thousands of umbral dots (UDs) in a mature sunspot in the active region NOAA 10667 at $\mu$=0.95. The data were acquired with the 1-m Swedish Solar Telescope on La Palma. With the help of a multilevel tracking (MLT) algorithm the sizes, brightnesses, and trajectories of 12836 umbral dots were found and analyzed. The MLT allows UDs with very low contrast to be reliably identified. Inside the umbra we determine a UD filling factor of 11%. The histogram of UD lifetimes is monotonic, i.e. a UD does not have a typical lifetime. Three quarters of the UDs lived for less than 150s and showed no or little motion. The histogram of the UD diameters exhibits a maximum at 225km, i.e. most of the UDs are spatially resolved. UDs display a typical horizontal velocity of 420m/s and a typical peak intensity of 51% of the mean intensity of the quiet photosphere, making them on average 20% brighter than the local umbral background. Almost all mobile UDs (large birth-death distance) were born close to the umbra-penumbra boundary, move towards the umbral center, and are brighter than average. Notably bright and mobile UDs were also observed along a prominent UD chain, both ends of which are located at the umbra-penumbra boundary. Their motion started primarily at either of the ends of the chain, continued along the chain, and ended near the chain's center. We observed the splitting and merging of UDs and the temporal succession of both. For the first time the evolution of brightness, size, and horizontal speed of a typical UD could be determined in a statistically significant way. Considerable differences between the evolution of central and peripheral UDs are found, which point to a difference in origin.

References in corpus (6)

• Magneto-convection in a sunspot umbra
• Properties of sunspots in cycle 23: I. Dependence of brightness on sunspot size and cycle phase
• Evidence of convective rolls in a sunspot penumbra
• Formation Process of a Light Bridge Revealed with the Hinode Solar Optical Telescope
• Stratification of sunspot umbral dots from inversion of Stokes profiles recorded by Hinode
• Umbral Fine Structures in Sunspots Observed with Hinode Solar Optical Telescope

Cited by in corpus (22)

• Magnetic Structure of Sunspots
• Modeling the Subsurface Structure of Sunspots
• Statistical Distribution of Size and Lifetime of Bright Points Observed with the New Solar Telescope
• Comparison of solar photospheric bright points between SUNRISE observations and MHD simulations
• Properties of simulated sunspot umbral dots
• Temporal Evolution of Velocity and Magnetic Field in and around Umbral Dots
• Morphology and evolution of umbral dots and their substructures
• Vertical flows and mass flux balance of sunspot umbral dots
• Active region fine structure observed at 0.08 arcsec resolution
• Striation and convection in penumbral filaments
• Properties of Umbral Dots as Measured from the New Solar Telescope Data and MHD Simulations
• Dark structures in sunspot light bridges
• Observations of Umbral Dots and their Physical Models
• The Observational Evidence for the Internal Excitation of Sunspot Oscillations Inferred from the Fe I 5435 A Line
• Investigation of Umbral Dots with the New Vacuum Solar Telescope
• Physical Characteristics of Umbral Dots Derived from a High Resolution Observation
• Structures in compressible magnetoconvection and the nature of umbral dots
• Sunspot Bright Points
• Investigating the relation between sunspots and umbral dots
• Chromospheric plasma ejection above a pore
• Ti I lines at 2.2 $\mu$m as probes of the cool parts of sunspots
• Umbral Dynamics in the Near Infrared Continuum