The Linear Polarization of Hydrogen H-Beta Radiation and the Joint Diagnostic of Magnetic Field Vector and Electron Density in Quiescent Prominences. II - the Electron Density
Résumé
Fourteen quiescent prominences of considerable height over the Solar surface have been observed simultaneously in the helium D3 and hydrogen Hβ lines: the linear polarization measurements which have been performed at the Pic-du-Midi Observatory have been interpreted by means of the Hanle effect theory (modification of polarization by the local magnetic field) and of the collisional depolarization theory. The present paper is devoted to the analysis of the results concerning the electron density Ne which have been obtained by this new method of diagnostic. Firstly, a straightforward interpretation of the measurements made by using the Hβ line polarization only has provided an upper limit for Ne, which remains lower than 7 1010 cm-3 in all cases. Secondly, by taking into account both the Hanle effect and the depolarization by collisions with the electrons and the protons of the medium, the actual electron density has been derived: it neighbours 1 1010 cm-3. As physically expected, Ne decreases with increasing height in prominences. Finally, our results have been compared to those obtained quite recently by different methods, which shows an evident tendency for Ne to get higher values in brighter prominences.