The quiet Sun magnetic field observed with ZIMPOL on THEMIS

Abstract

Context. The quiet Sun magnetic field probability density function (PDF) remains poorly known. Modeling this field also introduces a magnetic filling factor that is also poorly known. With these two quantities, PDF and filling factor, the statistical description of the quiet Sun magnetic field is complex and needs to be clarified. Aims. In the present paper, we propose a procedure that combines direct determinations and inversion results to derive the magnetic field vector and filling factor, and their PDFs. Methods. We used spectro-polarimetric observations taken with the ZIMPOL polarimeter mounted on the THEMIS telescope. The target was a quiet region at disk center. We analyzed the data by means of the UNNOFIT inversion code, with which we inferred the distribution of the mean magnetic field αB, α being the magnetic filling factor. The distribution of α was derived by an independent method, directly from the spectro-polarimetric data. The magnetic field PDF p(B) could then be inferred. By introducing a joint PDF for the filling factor and the magnetic field strength, we have clarified the definition of the PDF of the quiet Sun magnetic field when the latter is assumed not to be volume-filling. Results. The most frequent local average magnetic field strength is found to be 13 G. We find that the magnetic filling factor is related to the magnetic field strength by the simple law α = B 1 /B with B 1 = 15 G. This result is compatible with the Hanle weak-field determinations, as well as with the stronger field determinations from the Zeeman effect (kGauss field filling 1-2% of space). From linear fits, we obtain the analytical dependence of the magnetic field PDF. Our analysis has also revealed that the magnetic field in the quiet Sun is isotropically distributed in direction. Conclusions. We conclude that the quiet Sun is a complex medium where magnetic fields having different field strengths and filling factors coexist. Further observations with a better polarimetric accuracy are, however, needed to confirm the results obtained in the present work.

Center-to-limb variation of the area covered by magnetic bright points in the quiet Sun

“…In agreement with the turbulent dynamo scenario, quiet Sun magnetic fields come with strengths in the full range from almost zero to 2 kG (Sánchez Almeida & Lites 2000;Domínguez Cerdeña et al 2006;Martínez González et al 2008;Bommier et al 2009;Viticchié et al 2011). Even if they only fill a small fraction of the quiet photosphere, the part with strong kG fields may be particularly important for a number of reasons.…”

Hierarchical analysis of the quiet-Sun magnetism

“…Some researchers conclude that the field has to be close to isotropic (Martínez González et al 2008a;Bommier et al 2009;Asensio Ramos 2009), others conclude that the field is preferentially horizontal (Orozco Suárez et al 2007b;Lites et al 2008), and yet others show that stronger fields are preferentially vertical, becoming nearly isotropic in the weak flux density limit (Stenflo 2010). The main reason for these apparent controversial results is that, at our best current observational capabilities and polarimetric sensitivity, we do not resolve individual magnetic structures.…”

Fast inversion of Zeeman line profiles using central moments

“…To test our inversion code with real data, we used THEMIS/MTR observations obtained by Bommier on 2005 September 13, which were already presented in a paper dealing with azimuth ambiguity solution (Bommier et al 2011). They concern the 630.2 Fe i line and an active region located at L = −3.8 • and b = −11.7 • .…”