Photometric calibration of the international Ultraviolet Explorer (IUE) for high resolution spectra.

Abstract

We present and discuss the high resolution absolute calibration for the SWP, LWP and LWR cameras on board IUE. The calibration was implemented in routine processing on 27 December, 1987 at VILSPA and on 30 August, 1990 at GSFC. The calibration is applicable to high resolution spectra processed with the 'new' version of the IUE spectral image processing software which was implemented in routine on 10 November, 1981 at GSFC and 11 March, 1982 at VILSPA. The high resolution calibration, for the way it is defined, is primarily determined by the efficiency of the short or long wavelength spectrographs in the high resolution, relative to the low resolution observing modes. This interpretation is consistent with the high resolution calibration being the same for LWP and LWR spectra (which are obtained through the same spectrograph) and being constant with time. It is shown that the data extraction becomes critical for the higher orders of the IUE echelle spectrographs, causing high resolution calibration to depend on the data extraction algorithm used below about 1350 A in the SWP and below about 2350 A in the LWP and LWR cameras.