Never forget the overheads!

When writing a proposal, one aspect that deserves particular attention is the correct estimation of the total time budget, including overheads. Overheads refer to the time required for various actions and processes that are necessary for conducting observations but do not directly involve collecting scientific data. These include activities such as target acquisition, instrument configuration, telescope presets, and detector readouts.

Overheads depend on the instrument and strategy you plan to use. If overheads are underestimated at the proposal stage, you will pay for this later: the telescope time approved by the ESO panels corresponds to the total time allocated to your programme. Therefore, any underestimation of overheads will necessarily result in a reduction of the available exposure time during observation preparation. A summary of overheads for the VLT instruments is available here.

To properly estimate overheads, you can use the p2demo tool, a demo version of the Phase 2 software, p2.

p2demo includes tutorial folders for each instrument and observing mode, which allow you to explore example OBs. Within p2demo, you can copy, modify, and combine these tutorial OBs to simulate the preparation of your own observations. The tool then allows you to compute the total execution time, automatically accounting for the corresponding overheads as they would occur in real observations, so you can accurately estimate the time required for your programme.

Be aware that many users use this tool to familiarise themselves with p2. As a result, you will find not only the tutorial folders but also several user-created folders within each run. We recommend deleting your own test folder once you finish practising with p2demo.