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The Evershed effect observed with 0.2 arsec angular resolution

J. Sanchez Almeida·I. Marquez·J. A. Bonet·I. Dominguez Cerdena
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Abstract

We present an analysis of the Evershed effect observed with a resolution of 0.2 arcsec. Using the new Swedish 1-m Solar Telescope and its Littrow spectrograph, we scan a significant part of a sunspot penumbra. Spectra of the non-magnetic line Fe I 7090.4 A allows us to measure Doppler shifts without magnetic contamination. The observed line profiles are asymmetric. The Doppler shift depends on the part of the line used for measuring, indicating that the velocity structure of penumbrae remains unresolved even with our angular resolution. The observed line profiles are properly reproduced if two components with velocities between zero and several km/s co-exist in the resolution elements. Using Doppler shifts at fixed line depths, we find a local correlation between upflows and bright structures, and downflows and dark structures. This association is not specific of the outer penumbra but it also occurs in the inner penumbra. The existence of such correlation was originally reported by Beckers & Schroter (1969), and it is suggestive of energy transport by convection in penumbrae.

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J. Sanchez Almeida, I. Marquez, J. A. Bonet, I. Dominguez Cerdena. 2006-11-16. The Evershed effect observed with 0.2 arsec angular resolution. https://doi.org/10.1086/511254

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