Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005apj...622.1265c&link_type=abstract
The Astrophysical Journal, Volume 622, Issue 2, pp. 1265-1274.
Astronomy and Astrophysics
Astronomy
13
Line: Profiles, Polarization, Sun: Magnetic Fields, Sun: Prominences
Scientific paper
In this paper we discuss some general aspects of Stokes profile inversion in prominences using principal component analysis (PCA). First, we address the problem of departure of the formation of He I D3 from the optically thin approximation, dealing in a heuristic way with the inversion of the two visible components of the line, which are differently affected by radiative transfer. This modified inversion does not alter recently published results on the magnetic structure of quiescent prominences, in particular confirming the presence of magnetic fields significantly larger than average in limited regions. Second, we investigate the effect of line-of-sight integration of the polarization signals from different magnetic configurations, to determine whether PCA inversion could interpret an observed signal in terms of a single magnetic model with unrealistically large field strength. Our results show that this possibility is not statistically significant, and in addition the few models that are wrongly inverted show very peculiar geometries that are not found in our inversion of real data. This result also supports the reality of stronger than average fields in prominences. Finally, we further investigated the importance of full Stokes inversion for a correct diagnostic of magnetic fields in prominences. We show how the exclusion of Stokes V induces the appearance of a 90° ambiguity in the position angle of the magnetic field in the plane of the sky (in addition to the well-known 180° ambiguity). Inclusion of Stokes V proves to be important at all field strengths, even though Stokes Q and U should in theory be sufficient to retrieve the complete vector field information for field strengths in the Hanle depolarization regime. We also show how the inversion noise determined by the discreteness of the PCA database may be an additional source of the 90° ambiguity, even in the presence of Stokes V, therefore imposing a lower bound on the model density of the database.
Bevilacqua Riccardo
Casini Roberto
López Ariste Arturo
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