Non-LTE line formation for iron group elements. IV. NI ^44^Sc IV, ^44^Sc V and ^44^Sc VI.

A non-LTE line formation calculation for nickel in the ionisation stages ^44^Sc IV through ^44^Sc VI is introduced. The data for radiative bound-bound transitions which have been derived as part of this work are described and their accuracy is evaluated. The theoretical non-LTE spectrum of Ni^44^Sc IV, ^44^Sc V, ^44^Sc VI is compared to observations of BD+75 325 and Feige 67 both of which are classified as sdO stars. Together with the non-LTE spectrum of iron in the ionisation stages ^44^Sc IV through ^44^Sc VI this work provides a powerful tool for abundance analyses of iron group elements in objects such as sdO stars.