J.-C. Pecker

Theoretical study of the Fraunhofer lines polarization: the case of Ca I 4227.

The measurements by Brückner (1963) of the Ca i 4227 polarization at the Suns limb provides us with a test for the theory of line polarization. Computations are developed taking into account: (a) the transfer polarization, due to the anisotropy of radiation field; (b) the depolarizing collisions acting in the wings. The magnetic field is not taken into account and the theory is not valid in the Doppler core. In the wings a very good fit is obtained, using appropriate source-functions fitting the observed profiles at the center of the disk, and from center to limb.

Structure and physics of solar faculae. V : study of the roughness effect in the quiet chromosphere-corona transition zone

Taking into account the effect of roughness (or local departures from sphericity) of the emitting layers in the chromosphere-corona transition zone (CCT) allows one to determine the optical depths of layers responsible for resolved structures in Cii, Ciii, Oiv, and Ovi lines. The result, at the ‘top’ of the irregularities, is of the order of respectively τ1 ≥ 3.5,2.0, 1.6,0.5, and for the ‘bottom’ of these irregularities, τ2 = 0.7, 0.4, 0.3, 0.25. The characteristic angle of these irregularities is, respectively, of the order of 35 °, 33 °, 35 °, and 41 °. For unresolved structures of Civ and Ovi (already analyzed in the spherical symmetry hypothesis in Paper III), one finds τ1 ≈ 0.6; 0.9 and τ2 ≈ 0.12; 0.2 in the case of quiet areas; in the case of active areas, the range is broader for Civ and Ovi, from 1.0 to 1.7 for τ1 and from 0.2 to 0.9 for τ2. The values obtained from Ovi are in reasonable agreement with each other for resolved and unresolved structures. And the obtained values of τ1 and τ2 correspond not too badly with the determinations made in Paper III, by methods not exceedingly influenced by the spherical symmetry hypothesis.