Implementing TOPbase/Iron Project: continuous absorption from FeII

Abstract

We discuss implementation of TOPbase and Iron Project opacities for stellar spectral codes. We use a technique employed by Peach, where a Boltzmann-averaged cross-section is calculated for selected temperatures, and the opacity obtained from double interpolation in temperature and wavelength. It is straightforward to include all levels for which cross-sections have been calculated. Boltzmann-averaged cross-sections for FeII show a local maximum between 1700 and 2000 Å. We suggest this feature arises from 3d⁵4snl-> 3d⁵4pnl transitions within FeII. IUE spectra of iron-rich CP stars show local minima in this region. Theoretical calculations of a representative stellar continuum demonstrate that FeII photoionization contributes significantly to the observed minima.