On the inversion of Stokes profiles with local stray-light contamination

Abstract

Obtaining the magnetic properties of non-resolved structures in the solar photosphere is always challenging and problems arise because the inversion is carried out through the numerical minimization of a merit function that depends on the proposed model. We investigate the reliability of inversions in which the stray-light contamination is obtained from the same observations as a local average. In this case, we show that it is fundamental to include the covariance between the observed Stokes profiles and the stray-light contamination. The ensuing modified merit function of the inversion process penalizes large stray-light contaminations simply because of the presence of positive correlations between the observables and the stray-light, fundamentally produced by spatially variable systematics. We caution that using the wrong merit function, artificially large stray-light contaminations might be inferred. Since this effect disappears if the stray-light contamination is obtained as an average over the full field-of-view, we recommend to take into account stray-light contamination using a global approach.

5 pages, 3 figures, accepted for publication in ApJ

References in corpus (5)

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• Advanced Forward Modeling and Inversion of Stokes Profiles Resulting from the Joint Action of the Hanle and Zeeman Effects
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• On the validity of the 630 nm Fe I nm lines for the magnetometry of the internetwork quiet Sun
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Cited by in corpus (9)

• Spatially coupled inversion of spectro-polarimetric image data I: Method and first results
• Analysis of Quiet-Sun Internetwork Magnetic Fields Based on Linear Polarization Signals
• Inference of the chromospheric magnetic field orientation in the Ca II 8542 A line fibrils
• Spatial deconvolution of spectropolarimetric data: an application to quiet Sun magnetic elements
• Analytical maximum likelihood estimation of stellar magnetic fields
• Model selection for spectro-polarimetric inversions
• Upper limits to the magnetic field in central stars of planetary nebulae
• Limitations and biases in the retrieval of the polar magnetic field I: the role of the magnetic filling factor in Milne-Eddington inversions of simulated Hinode/SP data
• A stray light analysis for SO/PHI-HRT and an updated comparison of the inferred magnetic field with SDO/HMI