Autoguider

The limits for which the guide probe vignettes the field of view for ALFOSC and MOSCA was checked following the installation of the new guide camera. The software selecting guide stars was updated and is now set so that it works for all current cassegrain instruments. It was also found when using StanCam that in certain cases the pick-off mirror which re-directs the light to StanCam actually vignettes the guide probe, and the area affected was determined. The only effect of this is that in certain (very few) cases another guide star needs to be selected.

The guide star server software has been transported to a none IDL version. Also a new version of the guide star catalog was installed. Together with the new camera that was installed at the end of period 30, this dramatically increased the number of available guide stars. We had some case where no guide star was found on the predicted position, and a web tool was developed to provide positions of alternative guide stars. This problem was investigated further and we believe the problem was caused by selecting sources from the catalog based on their blue (J-plate) magnitude which apparently include many spurious detections. The guide star selection was switched to the red magnitudes which provides both less spurious detections and more detected sources that can be used by the guide camera.

In the current situation and under normal weather conditions we basically always require the use of a 5-magnitude neutral density `Grey' filter, and we are looking at the possibility to limit the area over which guide stars are selected to limit any problems when doing offsets where one wants to keep the same guide star. Limiting the area over which guide stars are selected might also be used in the future to improve the pointing.