A correction method for the sensitivity loss of the LWR camera on board the IUE satellite.

Abstract

The loss of sensitivity of the IUE LWR camera (1950-3300 A) is analyzed. A total of 308 low-resolution spectra of the five UV standard stars BD + 75 325, BD + 28 4211, BD + 33 2642, HD 93521, and HD 60753, obtained from 1978 to October 1983, are compared. The loss of sensitivity is found to vary rapidly with wavelength, reaching a maximum of 3 percent/yr at 2325 A. A simple correction algorithm is presented. Various checks are performed to ensure that the method works properly and is effectively able to bring all the LWR spectra onto the same absolute flux scale within the accuracy of the IUE calibration. The rate of sensitivity loss was fairly constant during all the years when the LWR was the routine long-wavelength IUE detector. After 1983, when it stopped being used regularly, the rate of degradation apparently increased.