Extending the life of the Cosmic Origins Spectrograph (COS) with new lifetime positions

Abstract

Since its installation on the Hubble Space Telescope in 2009, the Cosmic Origins Spectrograph (COS) has obtained thousands of spectra in the ultraviolet. Most of these observations have used the far ultraviolet (FUV) channel. The microchannel plates in the FUV detector are subject to gain sag, resulting in a loss of sensitivity as a function of time, so the spectra are regularly repositioned to mitigate this effect. The original operations concept allowed space for spectra to be placed at five separate Lifetime Positions (LPs) on the detector, and the last of these will become operational in October 2021. Recent investigations into extending the operations of COS beyond 2025 have led to the realization that the instrument is capable of supporting additional LPs if operational changes are adopted. As a result, we have begun planning for taking data at LP6, which will use an area on the detector originally thought to be unavailable, beginning in 2022. Exploratory work for this effort began in late 2020, and additional characterization and calibration will continue over the next year. Here we discuss our plans for operating COS at LP6 and beyond.