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Guide Star acquisition

The acquisition of guide stars has been automated by the routine FINDSTAR (copyright CJM 1987) which is run from the ADAM terminal. This program will initially prompt you to centre your program object on the TV - so make sure that the TV flat is in before running FINDSTAR (see Part III for the list of current commands for the A and G Box). An approximate outline for the CCD detector area can be drawn on the TV using a menu option. FINDSTAR then asks if automatic guide star searching is required. If it is NOT then you came ready prepared with a guide star position and you will be prompted for it. Note that the Equinox of the guide star RA and Dec must be the same as that of the source object entered on the telescope UI. If the RA and Dec you enter for the guide star translate into a valid autoguider position the probe will be moved to that position and the system will be ready for autoguiding. If the position is invalid you will be reprompted for the RA and Dec.

If you do not have a prepared guide star position then respond in the affirmative to the prompt about automatic searching. The telescope will then be offset to fields within reach of the autoguider. At each offset position you are given the choice of ACCEPTING a guide star, proceeding to the NEXT offset field or exiting from the program altogether if something has gone wrong.

The offset command takes a few seconds to implement so watch the telescope position error display to confirm that the telescope has settled at the new position BEFORE deciding on your response at the ADAM terminal. Note also that you must be ready to turn the TV gain down quickly as the telescope offsets in case an unacceptably bright object enters the field.

If a suitable looking guide star appears in the TV field move that star to the CCD centre marker on the TV using the handset controls BEFORE entering ACCEPT on the ADAM terminal. In this context a ``suitable" guide star is defined as one that is easily (i.e. not barely detectable) visible on the TV in DIRECT mode with the gain turned fully up. Not all of the sky area shown on the TV screen is accessible to the autoguider but at least on the first four offset fields the vast majority is so it is worth trying for any stars that appear on the TV. When you ACCEPT a star the FINDSTAR program will calculate the required guide probe position and if all is well you will get the message that the telescope is being reset to the source position. If the guider position is not reachable you will get a message to that effect and you must try for another star either in that field of in the NEXT. If the guide probe position is accepted and the telescope reset to the source object then wait for a ``probe movement complete" message on the ADAM terminal before touching the autoguider controls.