Calibration and operation of the faint object spectrograph (Fos)

The design and basic performance characteristics of the Faint Object Spectrograph (FOS), one of five instruments built for use on the Space Telescope observatory, is summarized briefly. The results of the recently completed instrument -level calibration are presented with special emphasis on issues affecting plans for FOS astronomical observations. Examples include such fundamental characteristics as: limiting magnitudes (system sensitivity and noise figures), spectral coverage and resolution, scattered light properties, and instrumental polarization and modulation efficiencies. Also gated toward intended users, a rather detailed description of FOS operating modes is given. The discussion begins with the difficulties anticipated during target acquisition and their hoped-for resolution. Both the “normal” spectroscopic operating modes of the FOS and its “exotic” features (e.g. spectropolarimetric, time-tagged, and time -resolved modes) are presented. The paper concludes with an overview of the activities to assure proper alignment and operation of the FOS within the entire Space Telescope system (orbital and ground- based).