Bibcode
Bellot Rubio, L. R.; Balthasar, H.; Collados, M.
Bibliographical reference
Astronomy and Astrophysics, v.427, p.319-334 (2004)
Advertised on:
11
2004
Journal
Citations
149
Refereed citations
123
Description
The magnetic and kinematic configuration of sunspot penumbrae is
investigated by performing an inversion of the Stokes profiles of three
infrared lines at 1565 nm. We use a two-component model atmosphere to
describe, at least to first order, the unresolved structure of the
penumbra. The observed Stokes profiles are successfully fitted,
including those exhibiting abnormal shapes. The results of the inversion
are consistent with the idea that the penumbra is formed by almost
horizontal flux tubes embedded in a more vertical background magnetic
field, as proposed by Solanki & Montavon (cite{Sol93}). The tubes
possess weaker fields than the background except in the very outer
penumbra, and carry most of the Evershed flow. We characterize the
radial variation of the magnetic field vector and the velocity vector in
these atmospheric components. In the middle penumbra and beyond, the
magnetic field and the flow in the tubes are seen to return to the solar
surface. Everywhere in the penumbra, there is a perfect alignment of the
magnetic field vector and the velocity vector in the component
describing the penumbral flux tubes. We find that the Evershed flow is
supercritical in many places of the outer penumbra, and supersonic at
some locations near the outer sunspot boundary. Based on these
inversions, we suggest that the azimuthal fluctuations in the average
magnetic field inclination and strength inferred from simple
one-component models are caused by fluctuations in the filling factor
(i.e., the fractional area of the resolution element occupied by flux
tubes), not by changes in the intrinsic magnetic and kinematic
properties of the background or the flux-tube atmospheres. Also, we
confirm the jump of magnetic field azimuth proposed by Müller et
al. (cite{Mul02}) to explain the observed net circular polarization of
infrared lines.