SIMBAD references

A technique is described to establish the relative response of spectroscopic detection systems in the XUV and the EUV. The procedure utilizes the 1s-3p and 2s-3p transitions in H-like ions and is illustrated in terms of the O VIII transitions located near λ16 (Lyβ) and λ102.4 (Hα). The procedure can provide an in situ reference for calibrating spectrometers in orbit. The technique may also be used to check the spectrometer response in the laboratory when investigating the XUV excess that has been found for Capella. The spectral resolution in our experiment (~40 mÅ) is high enough to obtain the desired results directly. At a somewhat lower spectral resolution, radiative-collisional modeling would have to be employed to interpret the contributions to the O VIII Hα line. Our data test such models and indicate that significant corrections may be necessary.