Principle telescope operation

The BMK10k’s operations system will be a clone of the STELLA Control System (SCS; Granzer et al. 2010, Adv. in Astr. 2010, ID980182). It is basically a slave of a dual-coincidence weather station, a building status input, and a target input. Target acquisition and tracking (no guiding is foreseen) is fully automated, even the pointing model could be (re)done remotely. The error handler of the SCS realizes when certain regions in the sky experience increased acquisition aborts or even unnatural large offsets. It does not need any human attendance for neither doing the pointing model nor for steady-state operation. Slew speed is fixed but slewing is always faster than CCD read out so that no additional time loss is expected from slewing to a new field. A master input file contains all field coordinates and position angles and can be edited (changed) any time. A dispatch scheduler would sequence the fields according to a merit function based on the actual conditions and fields already observed. For use with the rather slow slewing rate, field selection could be further optimized with respect to the unavoidable CCD read-out time. No further time loss due to slew-time overhead is expected then.

The (current) shutter design is prone to introducing shutter-effects which might pose a problem during twilight flat fielding. Correcting for shutter effects on the flat-fielding is possible, but introduces additional error sources, so the preferred solution would be to go to longer exposure times, where shutter effects are negligible or even vanish. This strategy might run into a brightness limit though; each pixel of the BMK10k will receive approximately four times the sky flux than our current system at the same site, implying that the BMK10k should be operated at ‘darker’ twilight. At those low sky-light levels, contamination with star light may render twilight flat-fielding unfeasible (tbd). A dome flat might be considered. However, it introduces the problem of true ‘flatness’ which back-reacts on the photometric accuracy.

Stacking consecutive images is possible posteriori. The dome operation is included in the SCS and consists of an initial slit opening in the evening and closing in the morning and dome tracking. Twilight time is reserved for on-sky flat fielding. Darks and biases are taken during daytime. Steady-state operation is to be halted for at least one annular maintenance episode which would be done when the PLATO field is out of view.

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