Establishing HZ43 A, Sirius B, and RX J185635-3754 as soft X-ray   standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE   spectrometer, and the ROSAT PSPC
  The absolute calibration of space-borne instruments in the soft X-ray regime rests strongly on model spectra of hot white dwarfs.   We analyze the Chandra LETG+HRC-S observations of the white dwarfs HZ43 A and Sirius B and of the neutron star RX J185635-3754 in order to resolve current uncertainties in the soft X-ray spectral fluxes and photospheric parameters of the three stars. We have obtained improved parameters for which fit the observations from the optical to the soft X-ray regime. Our approach allows us to quote their absolute spectral fluxes at selected wavelengths which may aid the calibration of other space-borne instruments. 
K. Beuermann (1), V. Burwitz (2), T. Rauch (3) ((1) Institut fuer   Astrophysik, Universitaet Goettingen, Germany, (2) Max-P...