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At the start of every WHIRCAM run, and whenever the telescope structure is
changed (eg if another instrument is changed during the day, which will cause
a slight shift in the telecope balance), a pointing calibration must be
performed on a set of astrometric stars. This is done by your TO, but it
must be done with respect to the WHIRCAM ALICE display. Therefore, go into
Movie mode (see § 3.5.4), choose the filter you'll be
using most of the night, set the integration time to 0.3 sec, and aquire the
first of the position standards (ask for the faint set, as the normal set
saturate on WHIRCAM). You now need to define the the telescope rotation
centre:
- (1) Position the telescope such that the star is
near the top edge of the ALICE display, and mark this with a whiteboard marker
pen.
- (2) Ask your TO to change the SKY PA to 180, and you'll see the star
describe a half circle on the ALICE display, and mark this new position
(If it looks like it will move off screen, mark the approximate centre of
rotation, go back to SKY PA 0, move the star closer to the rotation centre,
and start again.)
- (3) The telescope rotation centre will be the point halfway
between your two marks.
The TO should then centre each of the position standard stars on this centre.
You can find out where this centre is with respect to the WHIRCAM array by
going into the `Set_graphics', `statistics_window' menus, and
changing the X and Y position of the statistics box until it is centred on
the rotation centre.
Shaun Hughes
Thu Mar 14 14:48:38 GMT 1996