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Astron. Astrophys. 345, 999-1005 (1999)

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

N.-E. Raouafi 1,2, P. Lemaire 1 and S. Sahal-Bréchot 2

1 Institut d'Astrophysique Spatiale, Unité mixte CNRS - Université Paris XI, F-91405 Orsay, France
2 Département `Atomes et molécules en Astrophysique', Unité Associée au CNRS no 812, Observatoire de Paris-Meudon, 5 place Jules Janssen, F-92195 Meudon Cedex, France
(Nour-Eddine.Raouafi@medoc-ias.u-psud.fr; raouafi@obspm.fr; lemaire@ias.fr; Sylvie.Sahal-Brechot@obspm.fr)

Received 2 December 1998 / Accepted 4 February 1999

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 [FORMULA] 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.

Key words: polarization – Sun: corona – Sun: UV radiation

Send offprint requests to: N.-E. Raouafi
(raouafi@medoc-ias.u-psud.fr; raouafi@obspm.fr)

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© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999
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