In-flight calibration of the ROSAT HRI ultraviolet sensitivity

Comparing measured and estimated count rates of a few selected sample stars , we confirm the validity and provide the in-flight calibration of the ROSA T HRI UV/visible effective area model in Zombeck et al. The count rate esti mates for Betelgeuse derived with this model are in agreement with the meas ured HRI upper limit. This result is also confirmed in an erratum by et al. aimed at revising their Berghofer previous calculation, which was overesti mated by more than 2 orders of magnitude. Adopting this ROSAT HRI UV/visibl e effective area model and measured UV/visible spectra of a set of sample s tars covering the range of T-eff 3000-40,000 K, we have built the calibrati on curves to estimate UV/visible contamination count rates for any star of known and T-eff, m(v), N-H.