Abstract
Context.Optical interferometry is at a key development stage. The Very Large Telescope Interferometer (VLTI) has established a stable, robust infrastructure for long-baseline interferometry that is usable by general astronomical observers. The present second-generation instruments offer a wide wavelength coverage and improved performance. Their sensitivity and measurement accuracy lead to data and images of high reliability.Aims.We have developed the Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) to access, for the first time, high resolution imaging in a wide spectral domain. Many front-line topics are explored with this new equipment, including: stellar activity and mass loss; planet formation and evolution in the gas and dust disks around young stars; and environment interaction and accretion processes around super massive black holes in active galactic nuclei.Methods.The instrument is a spectro-interferometric imager in the transmission windows calledL,M, andN, from 2.8 to 13.0 microns, combining four optical beams from the VLTI’s unit or auxiliary telescopes. Its concept, related observing procedure, data reduction, and calibration approach, is the product of 30 years of instrumental research and has benefitted from the expertise developed in the frame of the VLTI’s first generation instruments. The instrument utilises a multi-axial beam combination that delivers spectrally dispersed fringes. The signal provides the following quantities at several spectral resolutions: photometric flux, coherent fluxes, visibilities, closure phases, wavelength differential visibilities and phases, and aperture-synthesis imaging.Results.This article provides an overview of the physical principle of the instrument and its functionalities. The motivation of the choice of the instrumental concept and the characteristics of the delivered signal are detailed with a description of the observing modes and of their performance limit. MATISSE offers four spectral resolutions inL&Mbands, namely 30, 500, 1000 and 3400, and 30 and 220 in theNband, and it provides an angular resolution down to 3 mas for the shortest wavelengths. The MATISSE stand-alone sensitivity limits are 60 mJy inLand 300 mJy inN. The paper gives details of the sensitivity limits for the different measurables and their related precision criteria, considering telescope configurations and spectral resolutions. We also discuss the gain provided with the GRA4MAT fringe tracker. An ensemble of data and reconstructed images illustrate the first acquired key observations.Conclusions.The instrument has been in operation at Cerro Paranal, ESO, Chile, since 2018, and has been open for science use by the international community since April 2019. The first scientific results are being published now.
Highlights
The mid-infrared optical interferometry methods, coupling an array of telescopes in a wavelength domain sensitive to the environmental background emission, were developed 30 years ago
Two methods are used to reduce the crosstalk to a level lower than the background generated photon noise existing at all spatial frequencies in the Fourier plane: (a) spatial modulation, as in the Very Large Telescope Interferometer (VLTI) near-infrared spectrometer AMBER (Petrov et al 2007) and (b) a combination with temporal modulation as in the VLTI mid-infrared spectrometer MIDI (Leinert 2003)
This increase in sensitivity will be partially limited by the current VLTI adaptive optics, but it should allow mapping of active galactic nuclei (AGN) over a broader luminosity range than previously possible, and in turn opens the possibility of a wide analysis of the relative interactions of radiation and gravity on the dust accretion and polar wind launching mechanisms
Summary
The mid-infrared optical interferometry methods, coupling an array of telescopes in a wavelength domain sensitive to the environmental background emission (i.e. from 3 to 13 μm), were developed 30 years ago. The Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) is the mid-infrared spectrograph and imager of the VLTI This second generation interferometric instrument, built on the expertise acquired on MIDI (Leinert 2003) and AMBER (Petrov et al 2007), will significantly contribute to several fundamental research topics in astrophysics. It focusses, for instance, on the inner regions of disks around young stars where planets form and evolve, the surface structure and mass loss of stars at different evolutionary stages and frequently in binary interactions, and the environment of black holes in active galactic nuclei (AGN).
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