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COS 2030: New Lifetime Positions for FUV Spectroscopy with the Cosmic Origins Spectrograph

Presentation #304.02 in the session Space-based Instruments — iPoster Session.

Published onJun 29, 2022
COS 2030: New Lifetime Positions for FUV Spectroscopy with the Cosmic Origins Spectrograph

The Cosmic Origins Spectrograph’s far-ultraviolet detector (COS/FUV) is affected by gain sag, where repeated exposure to photons results in a position-dependent loss of sensitivity as a function of time. To reduce the impact of gain sag and maximize the useful lifetime of COS, the location where spectra fall on the COS FUV detector is regularly changed to a new lifetime position (LP). Each move requires a new calibration effort, since resolution, sensitivity, the wavelength solutions, and the optimal focus change with detector position. For past LP changes, nearly all FUV settings have moved from the previous LP to the new one. In contrast, from Cycle 29 (2021–22) onward, nearly every LP is hosting a subset of the settings. For Cycle 29, LP5 was introduced for cenwaves 1291 through 1327 of the G130M grating, where the cenwave number is the approximate center of the wavelength range in angstroms. As was the case at LP4, there are restrictions on the use of detector segment B at LP5. Additionally, exposures with the G140L grating have moved from LP4 back to LP3. For Cycle 30, LP6 will be introduced for exposures with the G160M grating that are longer than approximately half an orbit. We discuss the calibration of the new LPs and key changes from the user perspective, and we encourage current and prospective COS users to monitor the COS website and other documentation for updates. These and future LP changes have the potential to extend UV science with COS into the 2030s.

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