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Indication of the Hanle Effect by Comparing the Scattering Polarization Observed by CLASP in the Lyα and Si III 120.65 nm Lines

Additional information

Authors
Ishikawa R., Bueno J. T. ., Uitenbroek H., Kubo M., Tsuneta S., Goto M., Kano R., Narukage N., Bando T., Katsukawa Y., Ishikawa S., Giono G., Suematsu Y., Hara H., Shimizu T., Sakao T., Winebarger A., Kobayashi K., Cirtain J., Champey P., Auch`ere F., epán J. v. S. ., Belluzzi L., Ramos A. A. ., Sainz R. M. ., Pontieu B. D. ., Ichimoto K., Carlsson M., Casini R.
Type
Journal Article
Year
2017
Language
English
Abstract
The Chromospheric Lyman-α Spectro-Polarimeter is a sounding rocketexperiment that has provided the first successful measurement of the linear polarization produced by scattering processes in the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In this paper, we report that the Si III line at 120.65 nm also shows scattering polarization and we compare the scattering polarization signals observed in the Lyα and Si III lines in order to search for observational signatures of the Hanle effect. We focus on four selected bright structures and investigate how the U/I spatial variations vary between the Lyα wing, the Lyα core, and the Si III line as a function of the total unsigned photospheric magnetic flux estimated from Solar Dynamics Observatory/Helioseismic and Magnetic Imager observations. In an internetwork region, the Lyα core shows an antisymmetric spatial variation across the selected bright structure, but it does not show it in other more magnetized regions. In the Si III line, the spatial variation of U/I deviates from the above-mentioned antisymmetric shape as the total unsigned photospheric magnetic flux increases. A plausible explanation of this difference is the operation of the Hanle effect. We argue that diagnostic techniques based on the scattering polarization observed simultaneously in two spectral lines with very different sensitivities to the Hanle effect, like Lyα and Si III, are of great potential interest for exploring the magnetism of the upper solar chromosphere and transition region.
Journal
Astrophysical Journal
Volume
841
Start page number
31
Keywords
irsol-refereed-scientific-papers