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 performed studies to move the Aperture Mechanism so that the 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 were used to determine the location of the new lifetime position, enable science at that location, and finally calibrate observations obtained there. The additional lifetime calibration program “Second COS FUV Lifetime Position: Wavelength Scales (FCAL1)” uses observations from programs 12805, 12806, and 12796.

Table 12.4: Lifetime Position Calibration Program

I. Identify the New Lifetime Position

12676 - COS/FUV Characterization of Detector Effects

12677 - COS/FUV Mapping of the Stray PtNe Light through FCA

12678 - COS/FUV Characterization of Optical Effects

II. Enable Science at the New Lifetime Position

12793 - Second COS FUV Lifetime Position: FUV Detector High Voltage Sweep (FENA1)

12795 - Second COS FUV Lifetime Position: Verification of Aperture and FUV Spectrum Placement (FENA2)

12796 - Second COS FUV Lifetime Position: Focus Sweep Enabling Program (FENA3)

12797 - Second COS FUV Lifetime Position: FUV Target Acquisition Parameter Update (FENA4)

III. Calibrate the New Lifetime Position

12805 - Second COS FUV Lifetime Position: Wavelength and Resolution Calibration (FCAL2)

12806 - Second COS FUV Lifetime Position: Flux and Flatfield Calibration and TDS Transfer (FCAL3)

12807 - Second COS FUV Lifetime Position: Verification of FUV BOA Operations (FCAL4)

Phase I was part of Cycle 18. Phases II and III took place during Cycle 19.