EDP Sciences
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Volume 417, Number 2, April II 2004
Page(s) 775 - 784
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20034452

A&A 417, 775-784 (2004)
DOI: 10.1051/0004-6361:20034452

Evidence for the Hanle effect in molecular lines

S. V. Berdyugina1, 2 and D. M. Fluri1

1  Institute of Astronomy, ETH Zentrum, 8092 Zurich, Switzerland
    e-mail: fluri@astro.phys.ethz.ch
2  Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland

(Received 6 October 2003 / Accepted 15 December 2003)

In many wavelength regions molecular lines dominate the second solar spectrum that results from coherent scattering. Scattering polarization is modified by magnetic fields via the Hanle effect. This allows us to explore the magnetic field regime with weak field strengths and mixed polarities, which is not seen with the Zeeman effect and thus contains complementary information. Molecular lines are particularly well suited to diagnose such turbulent fields because they exhibit a broad range of magnetic sensitivities within narrow spectral regions. Thus, it is possible to employ the technique of the differential Hanle effect, i.e. to obtain field strengths by observing polarization ratios in various lines. We have identified one R- and one P-triplet of C 2 at 5140 Å and 5141 Å, respectively, that satisfy all conditions to be used in the differential Hanle effect. Based on these lines we have developed a model that can diagnose turbulent magnetic fields using the Hanle effect. The tool is sensitive over a broad range of magnetic field strengths from a few Gauss up to several hundred Gauss. This tool has allowed us to find a significant Hanle depolarization of C 2 lines in quiet Sun observations, which corresponds to a magnetic field strength of $15\pm3$ G.

Key words: line: formation -- molecular processes -- polarization -- scattering -- Sun: atmosphere -- Sun: magnetic fields

Offprint request: S. V. Berdyugina, sveta@astro.phys.ethz.ch

© ESO 2004