SIMBAD references

Plane parallel and spherically symmetric model atmospheres for hot (T_eff=100000K) high gravity (logg=7.5) stars are calculated and compared for different hydrogen/helium abundance ratios. The effect of the abundance changes on the emergent radiation is studied. Strong dependence of the profile of the He II 4686Å line on the abundance is found for low helium abundances. Also, pronounced dependence on the abundance ratio is found for the hydrogen H_α line for high helium abundances. Combination of these two lines may serve as a powerful diagnostic tool for the determination of hydrogen/helium abundance ratio in hot white dwarfs.