Properties of simulated sunspot umbral dots

TL;DR

This study uses 3D radiative MHD simulations to analyze sunspot umbral dots, comparing their properties with high-resolution observations and revealing insights into their magnetic and velocity structures.

Contribution

It provides a detailed statistical analysis of simulated umbral dots and compares them with observations, highlighting consistencies and limitations of current simulations.

Findings

Larger umbral dots are brighter and have longer lifetimes.

Simulated properties largely match recent observations.

Small, short-lived umbral dots are not well reproduced in simulations.

Abstract

Realistic 3D radiative MHD simulations reveal the magneto-convective processes underlying the formation of the photospheric fine structure of sunspots, including penumbral filaments and umbral dots. Here we provide results from a statistical analysis of simulated umbral dots and compare them with reports from high-resolution observations. A multi-level segmentation and tracking algorithm has been used to isolate the bright structures in synthetic bolometric and continuum brightness images. Areas, brightness, and lifetimes of the resulting set of umbral dots are found to be correlated: larger umbral dots tend to be brighter and live longer. The magnetic field strength and velocity structure of umbral dots on surfaces of constant optical depth in the continuum at 630 nm indicate that the strong field reduction and high velocities in the upper parts of the upflow plumes underlying umbral dots are largely hidden from spectro-polarimetric observations. The properties of the simulated umbral dots are generally consistent with the results of recent high-resolution observations. However, the observed population of small, short-lived umbral dots is not reproduced by the simulations, possibly owing to insufficient spatial resolution.