In-Flight Calibration of the ROSAT HRI Ultraviolet Sensitivity

Comparing measured and estimated count rates of a few selected sample stars, we con—rm the validity and provide the in-—ight calibration of the ROSAT HRI UV/visible eUective area model in Zombeck et al. The count rate estimates for Betelgeuse derived with this model are in agreement with the measured HRI upper limit. This result is also con—rmed in an erratum by