Autoguider

When investigating the issue of the telescope pointing it has been noted that also errors of the guide probe can cause variations in pointing. The position of the guide probe is defined in turns of 1024 encoder steps (each $\sim$0.007 arcsec), where the system keeps track of how many turns has been made by checking the position frequently and deciding that a turn should be added or subtracted if there is a sudden change from large to small encoder values (or vice versa) is detected. This does allow for the possibility that some turns are missed (corresponding to 7 arcsec) which might accumulate over time. It turns out that the guide probe was only reinitialised when ever the TCS was rebooted. This has been changed such that sending the guide probe to park position will initialise the probe. The TCS now also monitors the behaviour of the guide probe and warns the observer if it detects a possible loss of turns.

A system is under development where guide stars are automatically detected and fully automatically (or after selection by the observer) moved into the guide box after which guiding is switched on. This system still needs to be verified under varying (weather) conditions, but it is clear that the automatic mode can not be used under all circumstances. One of the problems is the relative small computing power of the TCS computer, and the current plan is to move the image from the guide camera that is used to detect the stars to another computer. With the increased computing power and the possibility to use sophisticated image processing software that are widely available it should then be possible to make a very reliable search and detect program. This would allow the process of selecting a guide star to be controlled without direct interaction with the TCS. Together with the information about the guide star we plan to provide on the TCS Display application described above, this would provide the possibility to control the whole process of pointing the telescope, selecting a guide star and following the guiding process as part of remote observing applications.