Computation of NLTE model atmospheres using approximate lambda operators

A grid of NLTE model atmospheres for helium-rich sdO stars computed with the method of approximate lambda operators is presented. It covers for the first time the whole range of the (log T/eff/ log g) - diagram for these types of stars where the standard complete linearization technique fails. Model atoms are restricted at first to the commonly used standard of 22 NLTE levels and 6 hydrogen lines for reasons of consistency with a larger grid of model atmospheres, but for many of the parameter values model atmospheres have been computed with detailed hydrogen and helium model atoms with 43 NLTE levels and 109 lines as well. 10 refs