Research Note

Excitation and deexcitation processes in atom-Rydberg atom collisions in helium-rich white dwarf atmospheres

¹ University of Belgrade, Institute of physics, PO Box 57, 11001 Belgrade, Serbia
e-mail: vlada@ipb.ac.rs
² Institute Isaac Newton of Chile, Yugoslavia Branch, 11060 Belgrade, Serbia
³ Astronomical Observatory, Volgina 7, 11060 Belgrade 74, Serbia
⁴ Observatoire de Paris, 92195 Meudon Cedex, France

Received: 6 November 2012
Accepted: 14 February 2013

Abstract

We aim to show the importance of non-elastic excitation and deexcitation processes in He^∗(n) + He(1s²) collisions with the principal quantum number n ≥ 3 for helium-rich white dwarf atmospheres. We compare the efficiencies of these processes with those of the known non-elastic electron-He^∗(n) atom processes in the atmospheres of some DB white dwarfs. We show that in significant parts of the considered atmospheres, which contain weakly ionized layers (the ionization degree ≲10^-3), the influence of the studied atom-Rydberg atom processes on excited helium atom populations is dominant or at least comparable to the influence of the concurrent electron-He^∗(n)-atom processes.