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Astron. Astrophys. 342, L17-L20 (1999)

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Letter to the Editor

A calibration of the ROSAT HRI UV leak

T.W. Berghöfer 1,2, J.H.M.M. Schmitt 1 and M. Hünsch 3

1 Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany
2 Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
3 Institut für Theoretische Physik und Astrophysik der Universität Kiel, Olshausenstrasse 40, D-24118 Kiel, Germany

Received 16 November 1998 / Accepted 24 November 1998


The purpose of this paper is to present a detailed investigation of the Ultraviolet and visible sensitivity of the high-resolution imager (HRI) onboard the ROSAT X-ray satellite. We provide observational evidence that a recently published model (Zombeck et al. 1997) of the out-of-band quantum efficiency of the HRI overpredicts the detector response longward of approximately 4000Å. The contamination of the HRI is limited to the UV bandpass below approximately 4000Å. Based on the optical properties of our target stars, our ROSAT HRI and PSPC observations, and UV fluxes measured with the TD1 satellite, we provide an accurate calibration for the UV leak flux and present formulae to estimate UV leak count rates based on UV (1965Å) fluxes or stellar U magnitudes.

Key words: instrumentation: detectors – stars: early-type – X-rays: stars

Send offprint requests to: T.W. Berghöfer

© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998