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

Journal Article · Mon Apr 10 04:00:00 EDT 2017 · Astrophysical Journal Letters

DOI:https://doi.org/10.3847/2041-8213/AA697F· OSTI ID:22654496

Kano, R.; Narukage, N.; Ishikawa, R.; Bando, T.; Katsukawa, Y.; Kubo, M.; Giono, G.; Hara, H.; Suematsu, Y. ^[1]; Bueno, J. Trujillo ^[2]; Winebarger, A.; Kobayashi, K. ^[3]; Auchère, F. ^[4]; Ishikawa, S.; Shimizu, T.; Sakao, T.; Tsuneta, S. ^[5]; Ichimoto, K. ^[6]; Goto, M. ^[7]; others, and

---

1. National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
2. Instituto de Astrofísica de Canarias, La Laguna, Tenerife, E-38205 (Spain)
3. Marshall Space Flight Center, National Aeronautics and Space Administration (NASA), Huntsville, AL 35812 (United States)
4. Institut d’Astrophysique Spatiale, Université Paris Sud, Batiment 121, F-91405 Orsay (France)
5. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210 (Japan)
6. Hida Observatory, Kyoto University, Takayama, Gifu 506-1314 (Japan)
7. National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan)

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 α 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 α 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 ∼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.

• OSTI ID: 22654496
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 1 Vol. 839; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CHROMOSPHERE
EXTRAPOLATION
FORECASTING
HYDROGEN
LIMBS
MAGNETIC FIELDS
MAGNETISM
MODIFICATIONS
POLARIMETERS
POLARIZATION
SCATTERING
SENSITIVITY
SUN
THREE-DIMENSIONAL CALCULATIONS
ULTRAVIOLET RADIATION
ULTRAVIOLET SPECTRA