## 5. The effect of collisionsThe presence of free electrons and protons in the plasma of the spicule leads us to consider the effect of collisions between the scatterer and the surrounding particles. These implies that collisional rates have to be added in the statistical equilibrium equations for (Eq. (A1)). As an example we give the equations for the evolution of the populations and In these equations we have neglected the collisional rates due to inelastic collisions, with , since they are very small compared to those due to the elastic ones, with , (see Tables 5 and 6). The factor is defined by Sahal et al. (1996)
In order to find the solution for , we solve
symbolically the equations in the subsystem
with the collisional rates taken into account. This is possible
through Mathematica. The Stokes parameters For electronic densities less than
cm For higher densities one has to consider efficient inelastic collisional rates from the level which is by far the most populated. The relevant collisional rates, for a temperature K, are One can show that: with This expression reduces to the preceding one for (Eq. 15) when that is 1. We can introduce , the Stokes parameters when collisions are considered. For the angle of rotation of the polarization plane, we find The rotation angle is unaffected by
collisions due to the fact that the Stokes parameters
© European Southern Observatory (ESO) 1998 Online publication: April 28, 1998 |