APerture synthesis in the mid-infrared with the VLTI

Our objective is to develop of the mid-infrared imaging for the VLTI. Several areas of astrophysics will benefit of this new capability. APreS-MIDI comprises a beam combiner which interfaces with the current MIDI instrument. It thus constitutes an extension to the two-beam interferometric instrument MIDI by increasing the number of recombined beams up to four. This extension provides better uv-coverage (6 visibility points measured in one set) and moreover will allow measurement of 4 closure phase relations thus providing for the first time aperture synthesis images in the mid-infrared spectral regime. The mid-infrared spectral domain is very relevant for the study of the environments of various astrophysical sources. The science cases are broad. There are illustrated in the first part of this article by the perspective of imaging the circumstellar discs of young stellar objects. The APreS-MIDI instrument is described in a second part of this article.