Discovery of Scattering Polarization in the Hydrogen Ly alpha Line of the Solar Disk Radiation

0479158 - ASÚ 2018 RIV US eng J - Journal Article
Kano, R. - Trujillo Bueno, J. - Winebarger, A. - Auchere, F. - Narukage, N. - Ishikawa, R. - Kobayashi, K. - Bando, T. - Katsukawa, Y. - Kubo, M. - Ishikawa, S. - Giono, G. - Hara, H. - Suematsu, Y. - Shimizu, T. - Sakao, T. - Tsuneta, S. - Ichimoto, K. - Goto, M. - Belluzzi, L. - Štěpán, Jiří - Asensio Ramos, A. - Sainz, R.M. - Champey, P. - Cirtain, J. - de Pontieu, B. - Casini, R. - Carlsson, M.
Discovery of Scattering Polarization in the Hydrogen Ly alpha Line of the Solar Disk Radiation.
Astrophysical Journal Letters. Roč. 839, č. 1 (2017), L10/1-L10/6. ISSN 2041-8205. E-ISSN 2041-8213
Institutional support: RVO:67985815
Keywords : vacuum-ultraviolet spectropolarimeter * transition region * chromosphere
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 6.634, year: 2017

There is a thin transition region (TR) in the solar atmosphere where the temperature rises from 10,000 K in the chromosphere to millions of degrees in the corona. Little is known about the mechanisms that dominate this enigmatic region other than the magnetic field plays a key role. The magnetism of the TR can only be detected by polarimetric measurements of a few ultraviolet (UV) spectral lines, the Ly alpha line of neutral hydrogen at 121.6. nm (the strongest line of the solar UV spectrum) being of particular interest given its sensitivity to the Hanle effect (the magnetic-field-induced modification of the scattering line polarization). We report the discovery of linear polarization produced by scattering processes in the Ly alpha line, obtained with the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket experiment. The Stokes profiles observed by CLASP in quiet regions of the solar disk show that the Q/I and U/I linear polarization signals are of the order of 0.1% in the line core and up to a few percent in the nearby wings, and that both have conspicuous spatial variations with scales of similar to 10. arcsec. These observations help constrain theoretical models of the chromosphere-corona TR and extrapolations of the magnetic field from photospheric magnetograms. In fact, the observed spatial variation from disk to limb of polarization at the line core and wings already challenge the predictions from three-dimensional magnetohydrodynamical models of the upper solar chromosphere.
Permanent Link: http://hdl.handle.net/11104/0275156