The Automatic Telescope for Optical Monitoring (ATOM) is a 75 cm Ritchey-Chrétien telescope situated in Göllschau, Namibia, which forms part of the High Energy Stereoscopic System (H.E.S.S.). This paper presents ANDAQ, which allows to step from robotic to fully automatic observation by eliminating the need for daily human interaction. The main module responsible for the telescope operation forms a newly developed observer program, which also includes control of the telescope enclosure and offers various other tasks, like automated flat-fielding with live-analysis.

ANDAQ features its own TCP server for outside communication, making it possible to insert commands during the night. It possesses various means of monitoring internal and environmental parameters, and adjusts observation if necessary. This paper includes an description of the all-sky camera serving as cloud detector, supplemented by an additional rain detection device, and shows how operation is stopped as soon as weather parameters are below a defined standard, and automatically restarted once conditions recover. ANDAQ possesses a modular design based on a management core which starts and stops components as needed. This eases introduction of further functionality considerably and current development efforts include closer links to the main H.E.S.S. operation as well as live-analysis of exposures, allowing repeated observation in case of increased activity of a source.

ANDAQ has undergone extensive testing and has not seen any major problems so far. It may thus well serve as base for a future automated monitoring programme for the Cherenkov Telescope Array.

The High Energy Stereoscopic System (H.E.S.S.) in Namibia measures gamma-ray emission via the detection of Cherenkov light in the optical waveband and is therefore highly sensitive to changes in the transparency of the atmosphere. This is especially true for aerosols, small dust particles covering the sky at the H.E.S.S. site and severely reducing the atmospheric transparency for blue Cherenkov light for several days each year.

To quantify this effect, the Cherenkov Transparency Coefficient has been introduced as a hardware-independent parameter, which enables a correction of measured gamma-ray brightnesses.

Neighbouring the Cherenkov array, the Automated Telescope for Optical Monitoring (ATOM) operates an all-sky cloud camera as secondary instrument. Due to its high exposure frequency, the cloud camera may act as a detection system, if image parameters indicating low Cherenkov transparency are identified. However, the current instrument – originally conceived as a weather warning system – only produces white-light frames in low resolution. This study examines all frames taken with the current instrument since 2008 which coincide with H.E.S.S. observations in order to characterise relations with the measured Cherenkov transparency.

As a result of this preliminary study, trivial relations between the examined sky monitor observations and gamma-ray brightness can be excluded. However, it is planned to expand the scope of this activity with an upgraded device by introducing colour dependency and more advanced photometry with a larger number of objects in the near future.