NON-LTE LINE FORMATION FOR IRON-GROUP ELEMENTS .4. NI-IV, NI-V AND NI-VI

A non-LTE line formation calculation for nickel in the ionisation stag es IV through VI is introduced. The data for radiative bound-bound tra nsitions which have been derived as part of this work are described an d their accuracy is evaluated. The theoretical non-LTE spectrum of Ni IV, V, VI is compared to observations of BD+75 degrees 325 and Feige 6 7 both of which are classified as sdO stars. Together with the non-LTE spectrum of iron in the ionisation stages IV through VI this work pro vides a powerful tool for abundance analyses of iron group elements in objects such as sdO stars.