DEVELOPMENT OF AN OH-AIRGLOW SUPPRESSOR SPECTROGRAPH

A new spectrograph concept, the OH-airglow suppressor spectrograph (OH S), is presented. It has the unique capability of eliminating about 15 0 of the brightest OH airglow emission lines in the J- and H-bands. Th is greatly reduces the background emission, and thereby provides the h ighest sensitivity for photometric and low-resolution spectroscopic ob servations of extremely faint objects. A prototype OHS instrument has been built for the F/31 Cassegrain focus of the University of Hawaii 2 .2 m telescope and has been extensively tested in engineering and scie ntific observing runs. The suppression factor presently achieved is ap proximately 20 (which means that the sky background emission is reduce d to 1/20), and the throughput is approximately 34% in the OHS part, a nd about 5.5%, including the IfA HgCdTe NICMOS camera. The S/N gain of this instrument is expected to be around 1 mag compared to a standard spectrograph.