A feasibility study of future observations with MIDI and other VLTI science instruments: the example of the Galactic Center

Interferometry with the Very Large Telescope Interferometer (VLTI) will allow imaging of the Galactic Center and the nuclei of extragalactic sources at an angular resolution of a few milliarcseconds. VLTI will be a prime instrument to study the immediate environment of the massive black hole at the center of the Milky Way. With the MID infrared Interferometric instrument (MIDI) for example the enigmatic compact dust embedded MIR-excess sources within the central parsec should be resolvable. Further the observations of external galactic nuclei will allow unprecedented measurements of physical parameters (i.e. structure and luminosity) in these systems. With the exception of a few 'self-referencing' sources these faint-target observations will benefit from the available off-axis wavefront-correction system STRAP, working on suitable guide stars (GS). To fully exploit the use of VLTI within this context, the following questions have to be addressed among others: How feasible is blind-pointing on (faint) science targets? Are VLTI observations still efficiently feasible if these faint science targets exceed the usual angular distance (≤1 arcmin) to a GS candidate, enabling a standard closed-loop tip-tilt correction? How is the fringe-tracking procedure affected in densely populated regions such as the Galactic Center? What preparatory steps have to be performed to successfully observe these non-standard targets with the VLTI? In this contribution, we present aspects for the preparation of VLTI observations, which will be conducted in the near future. Considering these example observations of the Galactic Center region, several details of observing modes are discussed, which are necessary to observe such science targets. The final goal is the definition of observational strategies that are optimized for the discussed classes of targets, which provide properties touching the limits of VLTI observability.