Image above: The MATISSE cold optical bench (COB) prior to delivery. The COB, designed and constructed by NOVA, is the most complex part of the MATISSE instrument.

MATISSE (Multi-AperTure mid-Infrared SpectroScopic Experiment) is one of the second-generation instruments for the ESO Very Large Telescope Interferometer (VLTI). MATISSE is being built by a consortium consisting of  Observatoire de Cote de Azur (Nice), MPIA (Heidelberg), MPIfR (Bonn) and NOVA. MATISSE will coherently combine the light of all four 8-m VLT telescopes, synthesizing a telescope with an aperture of up to 130-m. Spatial resolving powers of 2 milliarcsec, similar to ALMA, are within reach. MATISSE can also make use of the mobile 1.8-m auxiliary telescopes (ATs), all relocatable in position, and capable of adding more baselines and thus improving the filling of the synthetic aperture and extending it to 200 meters.

MATISSE will measure coherent flux, visibilities, closure- and differential phases, as a function of wavelength in selected spectral bands and spectral resolutions. The multi-baseline capability will allow high dynamic range imaging  in the mid-Infrared. No other instrument in the world will offer similar capabilities, placing MATISSE at the forefront of infrared interferometry.

MATISSE can observe in the L, M, and N bands (resp. 3-4, 4.6-5 and 8-13 μm) and therefore well suited for study of Active Galactic Nuclei (AGNs), protoplanetary discs (e.g. T Tauri, Herbig AeBe stars), planetary debris disks (beta Pic types), the formation and evolution of planetary systems (e.g. young giant planets, hot Jupiter-like planets), the birth of massive stars, hot and evolved stars, as well as minor bodies of our solar system (asteroids, comets). There is major scientific interest from the universities of Leiden and Amsterdam. Scientific operations at the VLTI will begin in mid-2018.  The initial high priority projects for Dutch astronomers will be: mapping the angular/spiral structures in protoplanetary discs at scales comparable to the Earth’s orbit, both in thermal dust and in molecular gas emission; mapping the chaotic obscuring dust structures in AGNs and emission lines from molecules and shock-heated gas; possible direct detection of emission from hot Jupiter-like planets.

The NOVA-Op-IR group is responsible for the so-called Cold Optical Bench (COB), being the most complex part of MATISSE. It accommodates ~280 optical components, located into two boxes of roughly 70x70x40cm size, with in total over 56m(!) optical path length. There are 2 COBs, one for LM-band, the other for the N-band, allowing for simultaneous observation in both bands.

Each COB handles 4 telescope beams. All beams travel individual through the system and are only combined at the very end. The beams first are spatially filtered, then split up in an interferometric and photometric beam (for flux determination) and then anamorphically magnified (for reaching a different image scale in spectral and spatial direction). Thereafter the 8 beams are sent altogether to a filter-, polarizer and disperser unit. At the end the beams are combined by a camera system and focused on the detector, where the fringes are formed. MATISSE allows for dispersions between R30 and 5000, the latter to observe in detail the Br-alpha line and CO band centered around 4.05 and 4.8um.

The small envelope together with the complex functionality (each COB contains 17 mechanisms for configuration selection and alignment) required an unusual design approach: from the very beginning systems-, optical and mechanical engineers worked closely together, including suppliers, to define the concept, analyze the performance and finalize the design. For this instrument the philosophy of alignment by design was chosen, which required an extremely detailed Monte Carlo analysis and lead to a design with only one active alignment mirror per beam, avoiding the need of a time consuming and difficult alignment phase, and at the same time resulting in a very stable instrument. Without any doubt, MATISSE is the most challenging instrument built at NOVA so far.

Further information on MATISSE can be found on the project website.

The NOVA principal investigator for MATISSE is Prof. dr. Walter Jaffe (Leiden observatory).