The COS FUV channel: on-orbit performance trends and early characterization of a new detector lifetime position

摘要

The Cosmic Origins Spectrograph (COS) was installed into the Hubble Space Telescope in May 2009, and has beencollecting ultraviolet spectra since then. The Far Ultraviolet channel of COS uses an efficient optical design and a two-segment,large-format Cross Delay Line microchannel plate detector to obtain spectra at medium and low resolution inthe far ultraviolet. While the overall instrument performance has been excellent, several long-term trends in performancehave been noted and are being addressed. These include a slow decrease in overall sensitivity, which is independent ofthe illumination and may be due to a degradation of the photocathode with time.In addition, the detector microchannel plates are showing severe gain sag in the regions where the most photons havefallen. As a result, we are in the process of moving the spectra to a new, nearly pristine, location on the detector. Thiswill be the first of several additional lifetime positions which will allow us to collect high-quality spectra for many yearsto come. We will discuss the factors that led to our decision on where to move next and our progress in moving there,including details of the enabling and calibration activities which are being performed at the new location, and theanticipated performance. We will also address strategies that will be implemented in order to prolong the life at this andsubsequent positions.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.