IV.D. Internal Reference Source Stability

IRAS Explanatory Supplement
IV. In-Flight Tests
D. Internal Reference Source Stability

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Figure IV.D.1 The response of the individual detectors to the> internal refernece source compated to that from the planetary nebula NGC 6543 at 25 µm. The results from all the 25 µm detectors were combined after normalization to the mean response over the duration of the mission.
larger largest

During the course of the entire mission, the stability of the internal reference source as monitored at least daily relative to the planetary nebula NGC 6543. The result of this monitoring program at 25 µm for a large fraction of the mission are shown in Fig. IV.D.1. Let Ri,t be, for detector i and time t, the ratio of the amplitudes from the a flash of the internal reference source and from a scan over NGC 6543. If <Ri,j> is the mean ratio averaged over the duration of the mission, the quantity

Yi,t = (Ri,t/<Ri,t> - 1)

(IV.D.1)

is a direct measure of the stability of the internal reference source since the infrared output from NGC 6543 can be presumed to be stable. The quantity Yi,t is shown as the ordinate in Fig. IV.D.1 for all full-size detectors in the 25 µm band as a function of time from the star to the end of the mission. This wavelength band was selected for presentation since the signal-to-noise ratios for both the simulator flashes and NGC 6543 were the highest in this band. The dispersion in the measurements at 25 µm is 1.6%, well within the expected dispersion because of measurement uncertainties. The measurements in the 12, 60 and 100 µm bands give dispersions of 2.6, 1.7 and 2.7% respectively. The stability of the internal reference source is thus better than 2% throughout the mission.
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