Non Coherent Continuum Scattering as a Polarization Mechanism of the Enigmatic Ba _(II) D_1 Line

摘要

Line scattering polarization can be strongly affected by Rayleigh scattering by neutral hydrogen and Thomson scattering by free electrons. The assumption that continuum polarization can be modeled as coherent scattering, an excellent approximation far from the spectral line, yields a continuum depolarization when applied to an intrinsically unpolarizable spectral line. However, the radiation field is not always constant over the spectral line and continuum scattering has to be treated non-coherently. A recent investigation showed that the redistribution of the spectral line radiation due to the non coherence of the continuum scattering can significantly modify the shape of the emergent fractional linear polarization profiles, even yielding emission Q/I features in intrinsically unpolarizable lines. Here we show an application to the enigmatic D_1 line of Ba _(II) at 4934 ?, neglecting the hyperfine structure of the 18% of the barium isotopes whose nuclear spin is non-zero. We show that with this assumption Q/I signals above the continuum polarization level can be produced in solar atmospheric models representative of polar faculae.