High-resolution View into the Infrared Universe
First Light of the MATISSE Interferometer at ESO’s Very Large Telescope in Chile
After 12 years of design and development in Europe, the MATISSE interferometry instrument has been installed during the last 3 months at ESO’s Very Large Telescope (VLT). MATISSE combines four of the VLT telescopes to obtain an interferometer with an extremely high spatial resolution. This instrument allows astronomers to study the environment of young stars, the surfaces of stars and Active Galactic Nuclei in the mid-infrared wavelength range. In February 2018, this new, powerful and technically challenging instrument successfully achieved ‘First Light’. This achievement consummates the decade-long efforts of a large number of engineers and astronomers in France, Germany and in the Netherlands, including the infrared interferometry research group at the Max Planck Institute for Radio Astronomy in Bonn, Germany.
MATISSE is a second-generation Very Large Telescope Interferometer (VLTI) instrument providing extremely high spatial resolution. It is a combined imager and spectrograph for interferometry in the mid-infrared 3–5 μm spectral region (L- and M-bands) and the 8–13 μm region (N-band). MATISSE builds on the experience gained with the VLTI’s first-generation instruments, but vastly extends their capability to produce detailed images. The instrument exploits multiple telescopes and the wave nature of the light to produce more detailed images of celestial objects than can be obtained with any existing or planned single telescope. High- resolution imaging in the infrared is technically demanding but has yielded spectacular results in detecting planet-forming discs around stars, images of the surfaces of stars, and dusty discs around Active Galactic Nuclei.
The target of the First Light observation was the bright star Sirius (see Fig. 1). Figure 2 shows the ESO VLT, which consists of four telescopes with a mirror diameter of 8.2 m (the Unit Telescopes) and four telescopes with 1.8 m mirror diameter (the Auxiliary Telescopes).
Because of the technical challenges, only a few mid-infrared interferometers have observed prior to MATISSE: the SOIRDETE prototype at the Plateau de Calern in France, the ISI interferometer of the Berkeley University and the Keck interferometer in the US, and, the ESO-MIDI instrument. MATISSE is designed for a broad range of science goals with as prime science cases the studies of the discs around young stars and Active Galactic Nuclei.
The capability of MATISSE is unique in the world: It will open the infrared L-, M- and N-bands (respectively 3.0–4.1, 4.6–5.0 and 7–13 μm) to long-baseline infrared interferometry. The angular resolution in the L-band will be about 3 milliarcseconds (mas), equivalent to 0.3 AU for a star at 100 parsec distance. With various spectral resolutions between R ~ 30 and R ~ 5000, MATISSE can distinguish characteristic atoms and molecules in stars and galaxies. The second unique capability is high-fidelity mid-infrared imaging — closure-phase aperture-synthesis imaging — performed with up to four 8.2 m telescopes or 1.8 m telescopes.
“Single telescopes can achieve a maximum spatial resolution that is proportional to their mirror diameter. To obtain a higher resolution, we combine or interfere the light from four different VLT telescopes”, says Bruno Lopez from the Observatoire de la Côte d'Azur at Nice, the principal investigator of MATISSE. “This interferometric technique can provide us with a high spatial resolution that is proportional to the distance between the telescopes. Therefore, MATISSE is able to deliver the sharpest images ever in the 3–13 μm wavelength range.
Gerd Weigelt, Coinvestigator at the Max Planck Institute for Radio Astronomy, adds: “MATISSE will also allow us to obtain a high spectral resolution in addition to high spatial resolution. Therefore, we will be able to perform our studies in many different spectral channels distributed across an individual spectral line and even measure the velocity distribution in astronomical objects, which is very essential to reveal the physical properties of the objects.”
The MATISSE spectral bands will provide mid-infrared high angular resolution images that can be linked to observations at similar resolution in the submillimetre domain, with the Atacama Large Millimeter/Submillimeter Array (ALMA). MATISSE can be seen as a successor to MIDI (the MID-infrared Interferometric instrument) and a precursor of the future METIS instrument for the ELT.
The success of this MATISSE first light was only possible because of the hard and passionate work of many engineers and researchers and their institutes. Together with GRAVITY operating at the VLTI, MATISSE is a complex and challenging instrument: 3 tons, more than ten thousand elements machined and aligned to better than a thousandth of a millimetre, 20 cubic metres of volume.
Further testing of MATISSE will continue through 2018 and normal observations, open to all ESO astronomers, will begin early in 2019.
MATISSE was designed, funded and built in close collaboration with ESO, by a consortium composed of French (INSU-CNRS in Paris and OCA in Nice hosting the P.I. team), German (MPIA, MPIfR and University of Kiel), Dutch (NOVA and University of Leiden), and Austrian (University of Vienna) institutes. The Konkoly Observatory and Cologne University have also provided some support to the manufacture of the instrument.