Centering on objects using crosshair in panoramic mode

If the object is visually bright enough to see on the tip-tilt TV use this simple method. It assumes that the x-y stage is at its middle position and that the telescope has been positioned so that a star on the cross-hair is known to be accurately centered in the slit as verified using a nearby bright star.

There are two cases:

I.

The object is bright enough to guide on: This is easy: once centered, start guiding!

II.

The object is too faint to guide on directly:

You will need an offset guide star, either within the tip-tilt guide field (356 arcsec square, centered on optical axis) or the larger off-axis guide probe field (roughly 712 X 926 arcsec field north of the optical axis; see map).

A.

Tip-tilt guider:

1.

Move the telescope to center the object on the tip-tilt cursor with the stage in the middle position. (Panoramic mode)

2.

Move the stage to put the guide star on the cursor (Panoramic mode)

3.

Move the stage to put the star in the region of interest (ROI) and start guiding.

Once guiding is established, you can turn off the guiding and return the stage briefly to the middle position in the panoramic mode to confirm that the star is still centered. It is likely that some drift will have taken place and re-centering will be required. One then repeats the above procedure. If done quickly enough, it should converge with the object on the slit and the ROI on the guide star.

B.

Offset guider:

Center the object on the tip-tilt cursor in the middle position. Move the offset guide probe to acquire the guide star and start guiding. Once guiding is established, you can refine the centering on the tip-tilt cursor in panoramic mode, using offsets with follow on.