Proper Motions of Sunspots' Umbral Dots at High Temporal and Spatial Resolution

TL;DR

This study analyzes the high-resolution proper motions of umbral dots within a sunspot to understand their transient behaviors and flow patterns using advanced image processing and tracking techniques.

Contribution

It introduces a high-precision analysis of umbral dot motions using deconvolved images and Fourier local correlation tracking, revealing new flow patterns within sunspot umbrae.

Findings

Inward motion of peripheral umbral structures.

Detection of small-scale sink and source areas suggesting upflows and downflows.

Identification of two types of horizontal motions in umbral features.

Abstract

To deepen the analysis of the photometric properties of the umbra of a sunspot, we study proper motions of small features such as umbral dots (UDs) inside a single sunspot observed by the Solar Optical Telescope of Hinode close to the disk center. We consider horizontal flows with high precision and details to study the transient motion behavior of UDs in short time intervals. Blue continuum images were first deconvolved with the point-spread function, such that the stray light is precisely removed and the original resolution is improved. Several images were co-added to improve the signal-to-noise ratio, keeping a reasonable temporal resolution and checking that the results are reproducible. The Fourier local correlation tracking technique is applied to the new corrected time sequence of images, and horizontal velocity maps were obtained both for the whole umbra and for a high-resolution small region of the umbra to study the smallest details of the velocity fields. We used two different Gaussian tracking windows (0.8arcsec and 0.2arcsec), which reveals two types of horizontal motions for umbral features. First, a global inner penumbra and peripheral umbra inward motion directed to the central parts is revealed as an overall proper motion of bright peripheral fine structures. Second, motions matching small cells inside the darkest parts of the umbra with apparent sink and source areas are revealed, suggesting possible upflows and downflows appearing in different bright and dark locations without a definite answer regarding their brightness identification with a convective or a buoyant cell.