Fig. 3b-y : PPAK Target Acquisition and Guiding:
PMAS A&G Camera graphical user interface. The image shows a typical
acquisition frame as obtained when the telescope has slewed on-target,
encompassing a 3.4 x 3.4 arcmin^2 field-of-view. Contrary to the standard
IFU, which would be located in the middle of the dark central spot
(field mirror diaphragm), the PPAK IFU is mounted off-axis, outside
the field of view of the A&G camera
( Fig3b-z).
Accurate pointing is possible
by centering the extended target on the PPAK IFU overlay plot, and
applying a predefined offset (Pull-down Menu "Pointing"). The target
is then no longer visible on the screen. A sufficiently bright star can be
selected for offset-guiding. The guide star coordinates can be saved to disk.
Restoring these coordinates allows one to repeat observations in another
night with sub-arcsec pointing accuracy (note however the importance of
A&G camera filter selection and the effects of differential atmospheric
refraction). The image can also be plotted in a
reverse greyscale ,
stored as a postscript file for future reference, or sent to the printer.
Last update September 10, 2004 by M.
Roth