Bibcode
Martínez Pillet, V.
Bibliographical reference
Astronomy and Astrophysics, v.361, p.734-742 (2000)
Advertised on:
9
2000
Journal
Citations
99
Refereed citations
81
Description
The uncombed penumbral model proposed by Solanki & Montavon
(cite{sol93a}) is used to understand some recent observational results
found in penumbrae. This model uses a penumbral magnetic field
structured into horizontal flux tubes embedded in a more vertical
background field. A modified version of this model, with a weaker field
strength in the horizontal tubes, is used to explain the gradient with
height of field strength and inclination found in studies using
inversion techniques. These studies have found that over a range of 300
km, the field strength of the outer penumbra increases with height by
more than 500 G. Similarly, the field inclination decreases with height
by 30o in the same range of heights. We show that spectra
generated by the uncombed model can give rise to these two effects as
long as the horizontal tubes (of ~ 100 km diameter) remain unresolved.
We also study the linear, quadratic and rms fluctuations of the
inclination gradients that can be generated by the uncombed model. These
gradients are found to be compatible with those obtained from the null
divergence condition and those derived from observations of net circular
polarization. A key ingredient to explain these gradients is the
contribution of the two boundary layers that enclose the horizontal
magnetic tubes as seen by the line-of-sight. Our realization of the
uncombed model also predicts values of the net circular polarization
observed with the Advanced Stokes Polarimeter. The existence of a pure
background penumbral field as proposed by the model is, however, put
into question.