Convective motions and net circular polarization in sunspot penumbrae

Abstract

We have employed a penumbral model, that 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 net circular polarization 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 net circular polarization, as well as its dependence on the azimuthal and heliocentric angles.

Accepted for publication in the Astrophysical Journal. 10 pages, 7 figures (3 in color). Uses emulatedapj

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Cited by in corpus (10)

• Numerical sunspot models: Robustness of photospheric velocity and magnetic field structure
• Penumbral fine structure and driving mechanisms of large-scale flows in simulated sunspots
• Structure of sunspot penumbral filaments: a remarkable uniformity of properties
• A geometrical height scale for sunspot penumbrae
• Deep probing of the photospheric sunspot penumbra: no evidence for magnetic field-free gaps
• The electrical current density vector in the inner penumbra of a Sunspot
• Lateral downflows in sunspot penumbral filaments and their temporal evolution
• Searching for overturning convection in penumbral filaments: slit spectroscopy at 0.2 arcsec resolution
• Properties of the Umbral Filament Observed in Active Region NOAA 12529
• Three-lobed near-infrared Stokes V profiles in the quiet Sun