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THREE-DIMENSIONAL RADIATIVE TRANSFER SIMULATIONS OF THE SCATTERING POLARIZATION OF THE HYDROGEN LY alpha LINE IN A MAGNETOHYDRODYNAMIC MODEL OF THE CHROMOSPHERE-CORONA TRANSITION REGION
Stockholm University, Faculty of Science, Department of Astronomy.
Number of Authors: 4
2015 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 803, no 2, 65Article in journal (Refereed) Published
Abstract [en]

Probing the magnetism of the upper solar chromosphere requires measuring and modeling the scattering polarization produced by anisotropic radiation pumping in UV spectral lines. Here we apply PORTA (a novel radiative transfer code) to investigate the hydrogen Ly alpha line in a three-dimensional model of the solar atmosphere resulting from a state of the art magnetohydrodynamic (MHD) simulation. At full spatial resolution the linear polarization signals are very significant all over the solar disk, with a large fraction of the field of view (FOV) showing line-center amplitudes well above the 1% level. Via the Hanle effect the line-center polarization signals are sensitive to the magnetic field of the model's transition region, even when its mean field strength is only 15 G. The breaking of the axial symmetry of the radiation field produces significant forward-scattering polarization in Ly alpha, without the need of an inclined magnetic field. Interestingly, the Hanle effect tends to decrease such forward-scattering polarization signals in most of the points of the FOV. When the spatial resolution is degraded, the line-center polarization of Ly alpha drops below the 1% level, reaching values similar to those previously found in one-dimensional (1D) semi-empirical models (i.e., up to about 0.5%). The center to limb variation (CLV) of the spatially averaged polarization signals is qualitatively similar to that found in 1D models, with the largest line-center amplitudes at mu = cos theta approximate to 0.4 (theta being the heliocentric angle). These results are important, both for designing the needed space-based instrumentation and for a reliable interpretation of future observations of the Ly alpha polarization.

Place, publisher, year, edition, pages
2015. Vol. 803, no 2, 65
Keyword [en]
polarization, radiative transfer, scattering, Sun: chromosphere, Sun: magnetic fields, Sun: transition region
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-117728DOI: 10.1088/0004-637X/803/2/65ISI: 000353524500017OAI: oai:DiVA.org:su-117728DiVA: diva2:819149
Available from: 2015-06-10 Created: 2015-06-01 Last updated: 2017-12-04Bibliographically approved

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