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COS Instrument Handbook
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Cosmic Origins SpectrographInstrument Handbookfor Cycle 20 > Chapter 12: The COS Calibration Program > 12.6 FUV Lifetime Position Calibration Program

As described in Section 4.1.6, gain sag is beginning to affect spectra obtained with the FUV detector. To address this problem, the COS team is exploring the possibility of moving the Aperture Mechanism so that FUV spectra fall on a different part of the detector, called a lifetime position. This work is divided into three phases. Table 12.4 lists the programs that will be used to determine the location of the new lifetime position, enable science at that location, and finally calibrate observations obtained there.
Table 12.4: Lifetime Position Calibration Program
Phase I is currently underway (Cycle 18). Program IDs have been assigned to the FUV programs; the NUV programs are still under development. Phases II and III will take place during Cycle 19.

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