Analysis of a Fragmenting Sunspot using Hinode Observations

Abstract

We employ high resolution filtergrams and polarimetric measurements from Hinode to follow the evolution of a sunspot for eight days starting on June 28, 2007. The imaging data were corrected for intensity gradients, projection effects, and instrumental stray light prior to the analysis. The observations show the formation of a light bridge at one corner of the sunspot by a slow intrusion of neighbouring penumbral filaments. This divided the umbra into two individual umbral cores. During the light bridge formation, there was a steep increase in its intensity from 0.28 to 0.7 I_QS in nearly 4 hr, followed by a gradual increase to quiet Sun (QS) values in 13 hr. This increase in intensity was accompanied by a large reduction in the field strength from 1800 G to 300 G. The smaller umbral core gradually broke away from the parent sunspot nearly 2 days after the formation of the light bridge rendering the parent spot without a penumbra at the location of fragmentation. The penumbra in the fragment disappeared first within 34 hr, followed by the fragment whose area decayed exponentially with a time constant of 22 hr. The depleted penumbra in the parent sunspot regenerated when the inclination of the magnetic field at the penumbra-QS boundary became within 40 deg. from being completely horizontal and this occurred near the end of the fragment's lifetime. After the disappearance of the fragment, another light bridge formed in the parent which had similar properties as the fragmenting one, but did not divide the sunspot. The significant weakening in field strength in the light bridge along with the presence of granulation is suggestive of strong convection in the sunspot which might have triggered the expulsion and fragmentation of the smaller spot. Although the presence of QS photospheric conditions in sunspot umbrae could be a necessary condition for fragmentation, it is not a sufficient one.

Accepted for publication in ApJ; 15 pages, 15 figures, 1 table

References in corpus (8)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Detection of sea-serpent field lines in sunspot penumbrae
• Flow Field Evolution of a Decaying Sunspot
• Temporal evolution of the Evershed flow in sunspots. I. Observational characterization of Evershed clouds
• Magnetic Flux Loss and Flux Transport in a Decaying Active Region
• Properties of Umbral Dots from Stray Light Corrected Hinode Filtergrams
• Temporal evolution of the Evershed flow in sunspots. II. Physical properties and nature of Evershed clouds
• Resolving the Azimuthal Ambiguity in Vector Magnetogram Data with the Divergence-Free Condition: Application to Discrete Data

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