DEIMOS Throughput Upgrade

DEIMOS is Keck II’s workhorse optical spectrograph. It acts as an imager, a longslit spectrograph, and a multislit spectrograph. Its field of view (approximately 5' × 16') and multiplexing factor (up to about 200 slitlets) are the largest of Keck's instruments. However, the CCDs that comprise the science focal plane of DEIMOS are over two decades old. They no longer deliver state-of-the-art quantum efficiency (QE). Their QE is 60% at 420 nm and 920 nm, and it peaks at 87% at 780 nm. In 2025A, our team will replace the detectors with modern CCDs that will boost the throughput of DEIMOS by 70% at 400 nm, 10% at 700 nm, and 110% at 1000 nm. Replacing the cryostat also affords us the opportunity to modernize portions of DEIMOS's Flexure Compensation System. Most notably, the present focal plane moves within the cryostat for focus and flexure compensation. This upgrade will enclose the entire cryostat in a hexapod so that there will no longer be any cryogenic moving parts. This upgrade is a collaboration between the University of Notre Dame, Caltech Optical Observatories, Keck Observatory, and University of California Observatories. It is funded by the California Association for Research in Astronomy.