Spectropolarimetry of a decaying sunspot penumbra

Abstract

We report on high angular resolution, high precision spectropolarimetric measurements of a decaying sunspot. The spot gradually lost its penumbra during the course of three days. In the late stages of evolution where the only remnant of the spot is a naked umbra, we find small-scale inhomogeneities in the magnetic canopy surrounding it. The inhomogeneities are observed as finger-like structures of weak and nearly horizontal magnetic fields extending 1-2 arcsec from the outer border of the umbra. These fields are not associated with filamentary structures in continuum intensity, nor with conspicuous Evershed flows. The Stokes profiles emerging from the fingers exhibit blueshifts which we interpret as upward motions. This previously unknown fine structure may be related to penumbral field lines that no longer carry strong Evershed flows and rise to the chromosphere, producing the disappearance of the penumbra at photospheric levels.

Accepted for publication in ApJ

References in corpus (1)

• Flow Field Evolution of a Decaying Sunspot

Cited by in corpus (10)

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• No universal connection between the vertical magnetic field and the umbra-penumbra boundary in sunspots
• The formation and decay of sunspot penumbra in Active Region NOAA 12673
• The magnetic origin of the outer boundaries of sunspots
• The Decay Process of an α-configuration Sunspot
• Decay of a photospheric transient filament at the boundary of a pore and the chromospheric response