4MOST: science operations for a large spectroscopic survey program with multiple science cases executed in parallel

The 4MOST instrument is a multi-object spectrograph to be mounted to the VISTA telescope at ESOs La- Silla-Paranal observatory. 4MOST will deliver several 10s of millions of spectra from surveys typically lasting 5 years. 4MOST will address Galactic and extra-galactic science cases simultaneously, i.e. by observing targets from a large number of different surveys within one science exposure. This parallel mode of operations as well as the survey nature of 4MOST require some 4MOST-specific operations features within the overall operations model of ESO. These features are necessary to minimize any changes to the ESO operations model at the La- Silla-Paranal observatory on the one hand, and to enable parallel science observing and thus the most efficient use of the instrument on the other hand. The main feature is that the 4MOST consortium will not only deliver the instrument, but also contractual services to the user community, which is why 4MOST is also described as a 'facility'. We describe the operations model for 4MOST as seen by the consortium building the instrument. Among others this encompasses: 1) A joint science team for all participating surveys (i.e. including community surveys as well as those from the instrument-building consortium). 2) Common centralized tasks in observing preparation and data management provided as service by the consortium. 3) Transparency of all decisions to all stakeholders. 4) Close interaction between science and facility operations. Here we describe our efforts to make parallel observing mode efficient, flexible, and manageable.