Absorption non-symmetric ion-atom processes in helium-rich white dwarf atmospheres

International audienceIn this work, the processes of absorption charge exchange and photoassociation in He H collisions, together with the process of ion HeH photodissociation, are considered as factors influencing the opacities of the atmospheres of helium-rich white dwarfs in the far-UV and extreme ultraviolet (EUV) regions. It is shown that they should be taken into account even in the case of atmospheres of white dwarfs with H:He = 10-5. It is then established that in the case of white dwarfs with H:He ≳ 10-4, particularly when H:He ≈ 10-3, these processes have to be included ab initio in the corresponding models of their atmospheres, since in the far-UV and EUV regions they become dominant with respect to known symmetric ion-atom absorption processes