Convective Motions and Net Circular Polarization in Sunspot Penumbrae

We have employed a penumbral model, which includes the Evershed flow and convective motions inside penumbral filaments, to reproduce the azimuthal variation of the net circular polarization (NCP) in sunspot penumbrae at different heliocentric angles for two different spectral lines. The theoretical...

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Bibliographic Details
Published in:The Astrophysical journal 2010-01, Vol.709 (1), p.349-357
Main Authors: Borrero, J. M, Solanki, S. K
Format: Article
Language:English
Subjects:
Astronomy
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
ATMOSPHERES
Earth, ocean, space
Exact sciences and technology
FILAMENTS
MAGNETIC FIELDS
MAIN SEQUENCE STARS
MATHEMATICS
PHOTOSPHERE
POLARIZATION
SOLAR ACTIVITY
SOLAR ATMOSPHERE
STARS
STARSPOTS
STELLAR ACTIVITY
STELLAR ATMOSPHERES
SUN
SUNSPOTS
TOPOLOGY
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Summary:We have employed a penumbral model, which includes the Evershed flow and convective motions inside penumbral filaments, to reproduce the azimuthal variation of the net circular polarization (NCP) in sunspot penumbrae at different heliocentric angles for two different spectral lines. The theoretical NCP fits the observations as satisfactorily as penumbral models based on flux tubes. The reason for this is that the effect of convective motions on the NCP is very small compared to the effect of the Evershed flow. In addition, the NCP generated by convective upflows cancels out the NCP generated by the downflows. We have also found that, in order to fit the observed NCP, the strength of the magnetic field inside penumbral filaments must be very close to 1000 G. In particular, field-free or weak-field filaments fail to reproduce both the correct sign of the NCP and its dependence on the azimuthal and heliocentric angles.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/709/1/349