Absorption non-symmetric ion-atom processes in helium-rich white dwarf   atmospheres
  In this work the processes of absorption charge-exchange and photo-association in He+H$^{+}$ collisions together with the process of ion HeH$^{+}$ photo-dissociation are considered as factors of influence on the opacity of the atmospheres of helium-rich white dwarfs in the far UV and EUV region. It is shown that they should be taken into account even in the cases of the atmospheres of white dwarfs with H:He =$10^{-5}$. Than, it is established that in the cases of white dwarfs with H:He $\gtrsim 10^{-4}$, particulary when H:He $\approx 10^{-3}$, these processes have to be included \emph{ab initio} in the corresponding models of their atmospheres, since in the far UV and EUV region they become dominant with respect to the known symmetric ion-atom absorption processes. 
Lj.M. Ignjatovic, A.A. Mihajlov, V.A. Sreckovic and M. S. Dimitrijevic
astro-ph.SR