Issue |
A&A
Volume 662, June 2022
|
|
---|---|---|
Article Number | A13 | |
Number of page(s) | 6 | |
Section | The Sun and the Heliosphere | |
DOI | https://doi.org/10.1051/0004-6361/202243577 | |
Published online | 31 May 2022 |
Horizontal motions in sunspot penumbrae⋆
1
Astronomical Institute of the Czech Academy of Sciences (v.v.i.), Fričova 298, 25165 Ondřejov, Czech Republic
e-mail: michal.sobotka@asu.cas.cz
2
Schwendyweg 44, 13587 Berlin, Germany
Received:
17
March
2022
Accepted:
13
April
2022
Context. A model of penumbral filaments represented by magnetoconvective cells was derived recently from spectropolarimetric observations. This model resolves many of the inconsistencies found in the relations between intensity, magnetic, and velocity patterns in sunspot penumbrae.
Aims. High-resolution observations of horizontal motions in the penumbra are needed to complement the concept of penumbrae obtained from spectropolarimetry. Time series of intensity images of a large sunspot in AR 10634 acquired with the Swedish Solar Telescope in the G band and red continuum are analysed. The two simultaneous time series last six hours and five minutes.
Methods. Horizontal motions of penumbral grains (PGs), structures in dark bodies of filaments, the outer penumbral border, and G-band bright points are measured in time slices that cover the whole width of the penumbra and the neighbouring granulation. The spatial and temporal resolutions are 90 km and 20.1 s, respectively.
Results. In the inner penumbra, PGs move towards the umbra (inwards) with a mean speed of −0.7 km s−1. The direction of motion changes from inwards to outwards at approximately 60% of the penumbral width, and the mean speed increases gradually in the outer penumbra, approaching 0.5 km s−1. This speed is also typical of an expansion of the penumbra–granulation border during periods that typically last one hour and are followed by a fast contraction. The majority of the G-band bright points moves away from the sunspot, with a typical speed of 0.6 km s−1. High outward speeds, 3.6 km s−1 on average, are observed in dark bodies of penumbral filaments.
Conclusions. According to the model of penumbral filaments, it is suggested that the speeds detected in the dark bodies of filaments are associated with the Evershed flow and that the opposite directions of PG motions in the inner and outer penumbrae may be explained by the interaction of rising plasma in filament heads with a surrounding, differently inclined magnetic field.
Key words: Sun: photosphere / sunspots
Movies associated to Fig. 1 are available at https://www.aanda.org
© M. Sobotka and K. G. Puschmann 2022
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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