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Acquisition: Imaging observations

For a routine imaging observation the acquisition involves slewing to the target, acquiring the guide star, finding the target in the T-ReCS field of view, and waiting for the primary mirror tip/tilt corrections to be derived. Aside from making sure that proper guide stars have been selected, the only step in this process that involves T-ReCS is getting the object to the center of the field view.

In some cases, especially in observing standard stars which are point sources to T-ReCS, the astronomer carrying out the observations may chose to not bother moving the target to the array center. PIs can also skip the acquisition step if they so wish. This will save a small amount of setup time provided the object is found in the T-ReCS field of view. On the other hand it will cause a loss of time should the astronomer find that the target is poorly positioned.

To do imaging acquisition it is necessary to have an acquisition step defined. This must be a separate acquisition observation.

It is possible to skip the acquisition step for simple imaging observations if the target is a point source and if one does not care where the target ends up on the detector. Our experience from randomly selected standard stars and from queue observations without acquisition steps taken is that an object with a good position given in the OT file will appear somewhere in the central part of the T-ReCS field of view unless it has a significant proper motion, usually within a radius of 3 arc-seconds of the center of the field. This depends somewhat upon possible errors in the guide star position and the raw pointing accuracy of the telescope. If this is sufficient for the science program to be done, no acquisition step need be defined.

Instructions for creating a T-ReCS imaging acquisition step in the OT can be found on the Example Observations page