Direct Imaging of Fine Structure in the Chromosphere of a Sunspot Umbra

Abstract

High-resolution imaging observations from the Hinode spacecraft in the CaII H line are employed to study the dynamics of the chromosphere above a sunspot. We find that umbral flashes and other brightenings produced by the oscillation are extremely rich in fine structure, even beyond the resolving limit of our observations (0.22"). The umbra is tremendously dynamic, to the point that our time cadence of 20 s does not suffice to resolve the fast lateral (probably apparent) motion of the emission source. Some bright elements in our dataset move with horizontal propagation speeds of 30 km/s. We have detected filamentary structures inside the umbra (some of which have a horizontal extension of ~1500 km) which, to our best knowledge, had not been reported before. The power spectra of the intensity fluctuations reveals a few distinct areas with different properties within the umbra that seem to correspond with the umbral cores that form it. Inside each one of these areas the dominant frequencies of the oscillation are coherent, but they vary considerably from one core to another.

Accepted for publication in ApJ

References in corpus (4)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Magneto-convection in a sunspot umbra
• Can High Frequency Acoustic Waves Heat the Quiet Sun Chromosphere?
• Observations of Sunspot Oscillations in G band and Ca II H line with Solar Optical Telescope on Hinode

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• Shock Heating Energy of Umbral Flashes Measured with Integral Field Unit Spectroscopy
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• Downflowing umbral flashes as an evidence of standing waves in sunspot umbrae
• Spatial Distribution of Origin of Umbral Waves in a Sunspot Umbra
• First Observation of Chromospheric Waves in a Sunspot by DKIST/ViSP: The Anatomy of an Umbral Flash
• Fine wave dynamics in umbral flash sources
• Umbral Dynamics in the Near Infrared Continuum