On the ability of an extreme-ultraviolet multilayer normal-incidence telescope to provide temperature information for solar plasmas

In recent years, multilayer-coated optics have been used in solar-soft X-ra y and extreme-ultraviolet telescopes to record high-resolution, full Sun im ages. The multilayer coatings reflect efficiently over rather narrow wavele ngth bands that are selected to contain spectral emission lines considered to have plasma diagnostic importance for determining approximate electron t emperatures. The purpose of this Letter is to discuss the effect of continu um emission on the response of multilayer passbands and the effect of this response on temperature determinations in the 4 x 10(6)-2 x 10(7) K range. Significant effects are largely confined to continuum emission from flare p lasma. The flare free-free continuum in the EUV range is nearly temperature and wavelength insensitive and dominates the emission in passbands that ar e centered on quiet- to active-Sun coronal lines emitted by ions such as Fe IX-Fe XV.