Properties of Umbral Dots from Stray Light Corrected Hinode Filtergrams

TL;DR

This study uses high-resolution Hinode images to analyze umbral dots in sunspots, revealing finer structures and more accurate properties after stray light correction, aligning observations with larger telescopic and simulation results.

Contribution

It demonstrates the impact of stray light correction on the photometric and geometric analysis of umbral dots in high-resolution solar images.

Findings

Stray light correction increases image contrast by 1.45 times.

Identifies filamentary structures similar to penumbrae within umbrae.

Provides detailed statistics on umbral dot properties such as size, brightness, and motion.

Abstract

High resolution blue continuum filtergrams from Hinode are employed to study the umbral fine structure of a regular unipolar sunspot. The removal of scattered light from the images increases the rms contrast by a factor of 1.45 on average. Improvement in image contrast renders identification of short filamentary structures resembling penumbrae that are well separated from the umbra-penumbra boundary and comprise bright filaments/grains flanking dark filaments. Such fine structures were recently detected from ground based telescopes and have now been observed with Hinode. A multi-level tracking algorithm was used to identify umbral dots in both the uncorrected and corrected images and to track them in time. The distribution of the values describing the photometric and geometric properties of umbral dots are more easily affected by the presence of stray light while it is less severe in the case of kinematic properties. Statistically, umbral dots exhibit a peak intensity, effective diameter, lifetime, horizontal speed and a trajectory length of 0.29 I_QS, 272 km, 8.4 min, 0.45 km/s and 221 km respectively. The 2 hr 20 min time sequence depicts several locations where umbral dots tend to appear and disappear repeatedly with various time intervals. The correction for scattered light in the Hinode filtergrams facilitates photometry of umbral fine structure which can be related to results obtained from larger telescopes and numerical simulations.