lower flux (on average of $\sim 7\%$) of IUE, with respect to that of FOS (Gonzalez-Riestra 1998). The residual flux difference may be due to the fact that the IUE data were acquired a month later than the FOS spectra.

The G160L grating provides zero order light covering the full range between 1150 and 5500Å, with an effective wavelength at 3400Å, which provides useful simultaneous broad-band photometry. The flux calibration of the zero-order signal (Eracleous & Horne 1994) updated for errors and post-COSTAR sensitivity and aperture throughput (HST Data Handbook 1997) has been applied to the signal extracted in the zero-order feature of each of the 797 exposures.

 The IUE data
-------------

On October 15, 1995 ten IUE SWP (1150–1980Å) and ten LWP (1950–3200Å) low resolution ($\sim$ 6Å) spectra were acquired during consecutive 16h with exposure times equal or twice the $\rm P_{spin}$ to smear out effects of the rotational pulsation (Table1). The SWP and LWP exposures sample the orbital period.

The spectra have been re-processed at VILSPA using the IUE NEWSIPS pipeline used for the IUE Final Archive which applies the SWET extraction method as well as the latest flux calibrations and close-out camera sensitivity corrections (Garhart et al. 