Data acquisition

The way the telescope offset command in the data acquisition programs work, e.g., used in beam-switch mode which typically involves telescope offset sizes of 240 arcsec, has been improved. There is a allowed region for the guide-probe. In the past, a telescope offset which would move the guide probe outside the allowed area would not be executed. If this happened in the middle of script doing a dithering pattern this would mean that subsequent images would be taken in the wrong place. Now, the guide probe is stopped and autoguiding is switched off but the telescope offset is still performed. The observer can then acquire a new guide star and restart guiding without loosing the observing sequence.

To avoid images being effected by an integration starting before the telescope has come to a complete rest, some fine-tuning is still needed in the dithering procedures. Tests with very large dither steps (240 arcsec) and very short exposures (3s) with the HR camera in very good seeing (0.3 arcsec) have given some elongated/double stars. This must be improved at the TCS level such that a feedback is given from the TCS when the telescope is fully at rest (i.e., tracking/guiding). In this way the offset command given from the instrument knows when to start guiding. If guiding is started when the star is in the corner of the autoguider box, the telescope will be moved to get the star in the centre, and for short exposures in good seeing this produces elongated or double stars. While waiting for such an implementation in the TCS, sleep commands must be added in the scripts for observations with large dithers. Implementing a proper system will optimise the whole procedure as no exposure will be started too early or too late.

The first tests of the sequencer for NOTCam are under way and depending on the results it will be decided when to offer the sequencer in visitor mode. A plan will be made to define all the changes (specifically documentation) that are needed for a proper changeover.