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Detection of the O VI 103.2 NM line polarization by the SUMER spectrometer on the SOHO spacecraft

TitleDetection of the O VI 103.2 NM line polarization by the SUMER spectrometer on the SOHO spacecraft
Publication TypeJournal Article
Year of Publication1999
AuthorsRaouafi, N.-E., Lemaire P., and Sahal-Bréchot S.
JournalAstronomy and Astrophysics
Volume345
Pagination999-1005
Date PublishedMay
Abstract

The first detection of the O VI 103.2 nm line polarization has been performed in the corona by SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on the SOHO (Solar Heliospheric Observatory). The polarization properties of the spectrometer was used to analyze the solar radiation in a coronal hole at about 270 arcsec above the south solar limb, during the SOHO spacecraft rotation of March 19, 1996. Taking advantage of the different behavior of the lines in the O VI doublet and of the nearby chromospheric lines we have been able to extract the weak signal modulation introduced by polarization from solar variations and telescope scattered light. The \~ 4% modulation rate (related to the linear polarization of the O VI 103.2 nm line) derived is an important clue to infer the properties of the local magnetic field strength and the velocity field in the coronal hole.