Absorption spectra of NaHe from white dwarfs to helium clusters

Abstract

The absorption spectrum of Na produced in dense He shows line features, broadening and shift due to extrema in the 3s-3p potential differences of the transitions which contribute to the two fine-structure components. We present here a comprehensive study of NaHe collisional profiles at high density, and temperatures from 5000 K, the temperature prevailing in the atmosphere of ultra-cool white dwarfs, down to 1 K. At extremely low temperatures, experimental measurements and theoretical calculations of helium doped with alkali metals have been the subject of active study. The alkali-metal atoms are weakly bound to helium nanodroplets, and it appears that the dopants are trapped in a shallow dimple on the cluster's surface, rather being solvated inside the cluster.