Prime focus imaging spectrograph for the Southern African large telescope: operational modes

TLDR

Queue‑scheduled observing on a fixed‑altitude telescope demands rapid instrument reconfiguration between modes. PFIS is intended as the primary first‑light instrument for the Southern African Large Telescope. PFIS combines 5 VPH gratings (3200–9000 Å, R 1500–6000), a 6‑longslit/30‑mask system for 8′ field spectroscopy, a dual‑etalon Fabry‑Perot for imaging spectroscopy (R 500–12,500), a polarimetric subsystem with beam‑splitter and wave plates, and three rapid‑readout CCDs for >10 Hz time‑resolved sampling. These subsystems enable novel observing modes such as high‑time‑resolution multi‑object spectral polarimetry of accreting compact objects and Fabry‑Perot or imaging spectral polarimetry of nebulae and stellar clusters.

Abstract

The Prime Focus Imaging Spectrograph (PFIS) will be the workhorse first-light instrument on the Southern African Large Telescope (SALT). Scheduled for commissioning in late 2004, PFIS is a versatile high-throughput imaging spectrograph with a complement of 5 volume-phase holographic gratings for spectroscopic programs from 3200Å to 9000Å at resolutions of R=1500 to R=6000. A magazine of 6 longslits and 30 custom laser-milled slitmasks enables single- or multi-object spectroscopy over an 8 arcminute diameter field. With the gratings stowed, a dual-etalon Fabry-Perot subsystem enables imaging spectroscopy at R=500, R=3000, and R=12,500. The polarization subsystem, consisting of a polarizing beam-splitter used in conjunction with half- and quarter-wave plates, allow linear or circular polarimetric measurements in ANY of the spectroscopic modes. Three mosaiced rapid-readout frame-transfer CCDs provide the capability for time-resolved sampling at rates in excess of 10 Hz. Combinations of these subsystems permit novel observing modes for specialized scientific programs. Examples include high-time resolution multi-object spectral polarizmetry of accreting compact objects, and Fabry-Perot polarimetry or imaging spectral polarimetry of nebulae and stellar clusters. The demands of queue-scheduled observing on a fixed-altitude telescope require that the instrument be capable of rapid reconfiguration between modes.