Previous: The INT Faint Object Spectrograph
Up: The INT Faint Object Spectrograph
Next: Hardware description
Previous Page: The INT Faint Object Spectrograph
Next Page: Hardware description

Introduction

This guide attempts to introduce the observer to the Faint Object Spectrograph (FOS) as used on the Isaac Newton Telescope (INT). No detailed attempt is made to educate the reader concerning the workings of the detector (a Charge Coupled Device (CCD)) used with FOS; if the reader is interested, more details can be found in e.g. `A User Guide to the INT Prime Focus CCD', available in the INT control room, or from the LPUU at RGO.

Chapter 1 gives a brief description of the hardware and performance of FOS, chapter 2 details the setup and operational checks necessary to see that FOS is working properly, chapter 3 covers the operation of FOS in conjunction with the cassegrain Acquisition and Guidance (A&G) box and the INT Intermediate Dispersion Spectrograph (IDS) and chapter 4 shows the procedures contained in the online `quicklook' reduction procedures.

The Faint Object Spectrograph (FOS) is a highly efficient fixed format CCD based spectrograph, designed for low resolution (15-20Å) spectrophotometry, over a wide spectral range. The optical design, described by Charles Wynne (Optica Acta, 1982, 29, 1557) is based on a Schmidt camera working without a collimator in the diverging beam from the f/15 Cassegrain focus of the INT (see figure 1.1). The major components are shown in figures 1.2 and 1.3). The dispersion is provided by a transmission grating and a cross dispersing prism (grism), which together give a multi-order format covering the wavelength range 3400Å to 10,830Å. As a result of locating the CCD within the camera, there are a small number of optical surfaces and minimum vignetting, which produces a system which is more efficient than most conventional spectrographs. The fixed format enables FOS to have its own set of online data reduction and analysis procedures; the observer is then able to have calibrated data within a very short time of the completion of an exposure.

FOS is located beneath the IDS, using the same slit assembly, comparison sources and acquisition and guiding facilities. The change of IDS and FOS modes can indeed be made during the night, by moving a single folding prism, and installing or removing a light tight tube. The change from one mode to the other takes less than half an hour.