EDP Sciences
Free access
Volume 438, Number 2, August I 2005
Page(s) 727 - 732
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20042394

A&A 438, 727-732 (2005)
DOI: 10.1051/0004-6361:20042394

On the Sr I  $\mathsf{\lambda}$4607 Å Hanle depolarization signals in the quiet Sun

J. Sánchez Almeida

Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
    e-mail: jos@iac.es

(Received 19 November 2004 / Accepted 23 March 2005 )

The Hanle depolarization signals of Sr I $\lambda$4607 Å have been used to estimate the unsigned magnetic flux and magnetic energy existing in the quiet Sun photosphere. However, the Sr I $\lambda$4607 Å Hanle signals are not sensitive to the unsigned flux and energy. They only bear information on the fraction of photosphere occupied by magnetic field strengths smaller than the Hanle saturation, which do not contribute to the unsigned flux and energy. We deduce an approximate expression for the relationship between magnetic fill factor and Hanle signal. When applied to existing Hanle depolarization measurements, it indicates that only 40% of the quiet Sun is filled by magnetic fields with a strength smaller than 60 G. The remaining 60% of the surface has field strengths above this limit. Such constraint will be needed to determine the distribution of magnetic field strengths existing in the quiet Sun.

Key words: polarization -- Sun: magnetic fields -- Sun: photosphere

© ESO 2005

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