INTEGRAL is mounted in the Nasmyth No. 1 platform (GHRIL) of the WHT. The general layout of the system is shown in Figure 1 and a more detailed description of the focal plane area is shown in Figure 2.
A cylindrical structure (Acquisition, Guiding, and Calibration box structure) is bolted to the Nasmyth mechanical rotator. As this structure rotates synchronously with the focal plane when the telescope tracks, the sky position angle is fixed during an observation.
The Swing Plate (SP) is located in the telescope focal plane area, and this is the connection point for the acquisition and scientific fibre bundles. By rotating the SP any installed bundle can be placed at the centre of the focal plane, while the other bundles are light blocked. Hence, only one bundle at any one time can feed the spectrograph.
For acquisition a coherent fibre bundle transmits the light from the focal plane (via the SP) to a standard TV camera.
Figure 2: Focal plane area
Up to six scientific bundles can be simultaneously mounted in the SP, although in the standard configuration only three are used (called sb1, sb2, and sb3). These bundles are 5.5m long, while their fibre core diameter (in sky units) is: 0.45 (sb1), 0.9 (sb2), and 2.7 (sb3) arcsec respectively. The bundles are simultaneously connected at the entrance (pseudo-slit) of the WYFFOS spectrograph. They can be interchanged very easily, with an overhead of a few seconds. Hence, depending on the prevailing seeing conditions the instrument can be easily optimized for the scientific program.
Guide stars may be acquired by moving an XY slide containing two coherent fibre bundles. This unit moves in an off-axis region and the bundles feed a TV based autoguider.
A liquid fiber is used to feed a calibration source (currently Copper-Argon, Copper-Neon, or Tungsten lamps) to the focal plane.