Bibcode
DOI
Sánchez Almeida, J.; Márquez, I.; Bonet, J. A.; Domínguez Cerdeña, I.
Bibliographical reference
The Astrophysical Journal, Volume 658, Issue 2, pp. 1357-1371.
Advertised on:
4
2007
Journal
Citations
26
Refereed citations
22
Description
We present an analysis of the Evershed effect observed with a resolution
of 0.2". Using the new Swedish 1 m Solar Telescope and its Littrow
spectrograph, we scan a significant part of a sunspot penumbra. Spectra
of the nonmagnetic line Fe I λ7090.4 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-1 coexist in the resolution elements. Using
Doppler shifts at fixed line depths, we find a local correlation between
upflows and bright structures and between downflows and dark structures.
This association is not specific to the outer penumbra, but it also
occurs in the inner penumbra. The existence of such a correlation was
originally reported in 1969 by Beckers and Schröter, and it is
suggestive of energy transport by convection in penumbrae.