Electron scattering in the atmospheres of hot da white dwarfs

The process of high-frequency emission from the photosphere of hot, hydrogen-rich white dwarfs is reexamined in the light of the recent result of Boehm and Kapranidis that electron scattering has a strong influence on the energy distribution of these stars at extreme-ultraviolet (EUV) wavelenghts. Although electron scattering generally dominates the source function over a large range of depths, detailed model atmosphere calculations indicated that the EUV continuum is formed much deeper in the atmosphere, in a region where the source function is nearly completely thermal. This result is in agreement with Shipman's interpretation of the EUV flux as thermal emission from hot, deep-lying photospheric layers