Symmetric Atom–Atom and Ion–Atom Processes in Stellar Atmospheres

Abstract

Abstract:We present the results of the influence of two groups of collisional processes (atom-atom and ion-atom) on the optical and kinetic properties of weakly ionized stellar atmospheres layers. The first type includes radiative processes of the photodissociation/association and radiative charge exchange, the second one the chemi-ionisation/recombination processes with participation of only hydrogen and helium atoms and ions. The quantitative estimation of the rate coefficients of the mentioned processes were made. The effect of the radiative processes is estimated by comparing their intensities with those of the known concurrent processes in application to the solar photosphere and to the photospheres of DB white dwarfs. The investigated chemi-ionisation/recombination processes are considered from the viewpoint of their influence on the populations of the excited states of the hydrogen atom (the Sun and an M-type red dwarf) and helium atom (DB white dwarfs). The effect of these processes on the populations of the excited states of the hydrogen atom has been studied using the general stellar atmosphere code, which generates the model. The presented results demonstrate the undoubted influence of the considered radiative and chemi-ionisation/recombination processes on the optical properties and on the kinetics of the weakly ionized layers in stellar atmospheres.

Ionization cross section by electron impact of helium-like ions

“…in unit of 10 -20 cm 2 . 𝜎 Regarding the variation of the cross sections with z, it is clear that for the three levels 1 1 S, 2 1 S and 2 3 S the maximum values of the cross sections are inversely proportional to the values of z for the three helium like ions, as also indicated by the shapes of the figures 1, 2 and 3.…”

“…Electron impact ionization (EII) of atoms and molecules was studied during the last hundred years, from the very early days of modern physics [1]. The cross sections and ionization rates are atomic data that have important applications in astrophysics and plasma physics [2,3]. Several research works have been carried out in the calculation of ionization cross section using different methods [4], including classical methods [5], Coulomb Born approximation [6] and semi-empirical equations [7].…”

Chemi-ionization processes in Narrow-Line Seyfert 1 Galaxies

“…When an electron is excited into a high lying Rydberg state, with large principal quantum number, even inelastic thermal collisions can be sufficiently energetic to lead to ionization reactions [3,4]. These types of reactions can be classified as chemi-ionization reactions (associative ionization and non-associative ionization),…”