Nour-Eddine Raouafi Magnetic and Velocity Fields in the Solar Corona Outline Polar Holes: Latest Results SUMER: The Polarimeter Conclusions

LOS  Open superradial expanding field lines  Source of the fast solar wind Area of interest : polar coronal holes

Very broad line profiles emitted by heavy ions (O VI, Mg X ) in the polar coronal holes UVCS Results

Wave-particle energy exchange at cyclotron frequencies of the solar wind species High anisotropies in the velocity distributions of the scattering atoms Impact on the mechanisms of acceleration & heating of the coronal plasma Interpretation of UVCS observations

Atmospheric parameters: electron density Guhathakurta & Holzer (1994); Guhathakurta et al. (1999); Cranmer et al. (1999) & Esser et al. (1999) : power series DKL

O VI : Total Intensities The observed intensities are reasonably reproduced by most of the density models (DKL, GH94, Cra99) Guh99 & Ess99 give relatively low intensities at low altitudes (Raouafi & Solanki, 2004b)

O VI : Widths & Intensity Ratios  The LOS-integrated profiles are very sensitive to the density stratification details  DKL density stratification gives line widths comparable to the observed ones  The calculated intensity ratios are relatively close to the observed ones (except for Guh99 & Ess99) (Raouafi & Solanki, 2004a,b)

N.-E. Raouafi P. LEMAIRE S. Sahal-Brechot

The SOlar & Heliospheric Observatory (SOHO ) mission The S olar U ltraviolet M easurements of E mitted R adiation  Three-axis stabilized  Capacity of rolling around z-axis Objectives...; Coronal heating & Sources & acceleration of the solar wind (CDS, UVCS, EIT, LASCO & SUMER )

SUMER’s Optical Design  Capability of rastering  Sensitivity to the polarization

Observations  Date: SoHO roll of March 19, 1996  Target: An area in the polar coronal hole at ~1.3 R   Goal: Observe this area angles with respect to the polar axis

Wavelength range: 1022 – 1042 Å H I Ly-  1025 Å O VI Å & Å

Results Variation of the intensity ratio of the O VI doublet with the angle of observation Signature of the polarization of the O VI Å

Results p = 9 ± 2 %  = 9 ± 6° r = 2.88 ± 0.05 (Raouafi et al. 2002a) First determination of the polarization parameters of a UV line in the corona

Polarization measurements & Quantum theory of matter-radiation interaction (Raouafi 2002) Constraints on the   Coronal magnetic field: Hanle effect (< 3 Gauss)   Solar wind velocity vector: Doppler redistribution (40 – 70 km s -1 ) (Raouafi et al. 2002a,b) Interpretation of the observations

Conclusion SUMER SUMER showed us the way to infer the coronal magnetic field & the solar wind velocity vectors through the Hanle effect and the Doppler redistribution.