This is mainly used with the prime focus CCD camera. The A&G unit is mounted on a rotator, which allows the detector to be rotated to any position angle, although it is normally operated at one of the cardinal points. The default orientation is 180. The following facilities are provided:
[ TIFF ]
Figure: The area within which guide stars may be selected for use with the autoguider at the prime focus of the INT. (a) Scale drawing of the locations of chip, rotator axis and guide-star acquisition field, showing probe-coordinate limits. (b) A sketch showing the general relation between guide probe and sky coordinates for any PA.
The detector is an FW-130 image dissector with an S-20 photocathode. As there is insufficient space to accommodate a filter wheel or slide, a single fixed filter is used with the autoguider. The choice of this filter is a compromise between a match to the FW-130 response and to the spectral response of the instruments used at prime focus. At present a broad-band green filter is used.
Ideally guide stars should be selected in advance of the observing run, using GSS or Figure which shows the area of sky within which guide stars may be selected. Alternatively, they may be selected from the finder telescope, and then acquired by scanning a 2.5 2.5 arcmin area around the selected position. Stars with magnitudes in the range 7 < m < 13 will probably be suitable.