WYFFOS/AUTOFIB2 on the WHT

Astrometry

What sort of accuracy do I need?

Currently the postioning/guiding error of Autofib2 amounts to approximately 0.4 arcsec; see the CATALOGUES program at Cambridge. If working with objects from CCD frames, you must ensure that you set up the secondary astrometric reference frame based on the APM positions of the brighter (unsaturated) stars in the CCD field. Recent work with COSMOS suggests that positions obtained with this measuring machine may not be sufficiently accurate over the large field available with WYFFOS/AUTOFIB2.

What sort of fiducials do I need?

There are quite severe limitations imposed in the placing of fiducial guide fibres within the WYFFOS/AF2 field. A large number (>>20) of candidate fiducial stars must be input into the