Electron Densities in Quiescent Prominences Derived from Eclipse Observations

We develop a diagnostic tool for determination of the electron densities in solar prominences using eclipse data. The method is based on analysis of the hydrogen Balmer-line intensities (namely Hα and Hβ) and the white-light emission due to Thomson scattering on the prominence electrons. Our approach represents a generalization of the ratio method already used by Koutchmy, Lebecq, and Stellmacher (Astron. Astrophys. 119, 261, 1983). In this paper we use an extended grid of non-LTE prominence models of Gouttebroze, Heinzel, and Vial (Astron. Astrophys. Suppl. Ser. 99, 513, 1993) and derive various useful relations between prominence radiation properties and electron densities. Simultaneously, an effective geometrical thickness of the prominence can also be obtained. As an example we apply our general technique to original eclipse data of Koutchmy, Lebecq, and Stellmacher (Astron. Astrophys. 119, 261, 1983). Finally, we use our results to determine the color of prominences as it should be seen during total eclipses.