Nour-Eddine Raouafi
Magnetic and Velocity Fieldsin 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
10010
||T
T
Atmospheric parameters: electron density
SRrTk
SRSGpm
SRNrN
11
av
2
Be )(e )(e
1997) al.et Lamy &
1999 al.et Kohl 1999; al.et (Doyle DKL
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 tothe observed ones(except for Guh99 & Ess99)
(Raouafi & Solanki, 2004a,b)
N.-E. RaouafiP. LEMAIRE
S. Sahal-Brechot
The SOlar & Heliospheric Observatory
(SOHO) mission
The Solar Ultraviolet Measurementsof Emitted Radiation
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 polarcoronal hole at ~1.3 R
Goal:Observe this areaangles with respectto the polar axis
Wavelength range: 1022 – 1042 Å
H I Ly- 1025 ÅO VI 1031.92 Å & 1037.61 Å
Results
Variation of the intensityratio of the O VI doublet
with the angle of observation
Signature of thepolarization of theO VI 1031.92 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
ConclusionSUMERSUMER showed us the way to infer thecoronal magnetic field & the solar windvelocity vectors through the Hanle effect
and the Doppler redistribution.