MATISSE is foreseen as a mid-infrared spectro-interferometer combining the beams of up to four UTs/ATs of the Very
Large Telescope Interferometer (VLTI) of the European Southern Observatory. The related science case study
demonstrates the enormous capability of a new generation mid-infrared beam combiner.
MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. MIDI is a very successful
instrument which offers a perfect combination of spectral and angular resolution. New characteristics present in
MATISSE will give access to the mapping and the distribution of the material (typically dust) in the circumstellar
environments by using a wide mid-infrared band coverage extended to L, M and N spectral bands. The four beam
combination of MATISSE provides an efficient UV-coverage : 6 visibility points are measured in one set and 4 closure
phase relations which can provide aperture synthesis images in the mid-infrared spectral regime.
A first generation of VLTI (Very Large Telescopes Interferometer) focal instruments, AMBER in the near-infrared and MIDI in the mid-infrared, has been already integrated and tested. New and important science results have been obtained. These instruments combine two (for MIDI) or three (for AMBER) beams coming from the eight telescopes installed at Cerro Paranal (four 8-meters and four 1.8-meters telescopes). In order to improve the capabilities of the interferometer and to engage a new scientific prospective, the second generation of VLTI instruments is currently under study. MATISSE belongs to this second generation. MATISSE objective is the image reconstruction. It will extend the astrophysical potential of the VLTI by overcoming the ambiguities existing in the interpretation of simple visibility measurements. It is a spectro-interferometer combining up to four beams with a large spectral coverage ranging from 3 to 25 μm (L, M, N and Q bands). Different spectral resolutions (between 30 and 1500) are foreseen. MATISSE will measure closure phase relations thus offering an efficient capability for image reconstruction. The concept of MATISSE is presented in this paper. The recombination mode of MATISSE is similar to the AMBER beam combination, but has been adapted to the constraints specific to the mid-infrared domain.
Our objective is the development of mid-infrared imaging at the VLTI. The related science case study demonstrates the enormous capability of a new generation mid-infrared beam combiner. MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI by increasing the number of recombined beams up to four. MIDI is a very successful instrument which offers a perfect combination of spectral and angular resolution. New characteristics present in MATISSE will give access to the mapping and the distribution of the material (typically dust) in the circumstellar environments by using a wide mid-infrared band coverage extended to L, M, N and Q spectral bands. The four beam combination of MATISSE provides an efficient UV-coverage: 6 visibility points are measured in one set and 4 closure phase relations which can provide 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 environment of various astrophysical sources. Our science case studies show the wide field of applications of MATISSE. They will be illustrated in the first part of this presentation through the perspective of imaging the circumstellar environments/discs of young stellar objects. The MATISSE characteristics will be given in a second part of the presentation.
We are studying an optical concept aiming at recombining four mid-infrared telescope beams, where interference fringes are sampled in the pupil plane. Such a principle is perfectly adapted for reconstructing images by aperture synthesis with teh VLTI. It could be used for building a new generation 10 μm instrument, but instead of doing a totally new instrument, we propose the design of an optical module that can supply the surrent MIDI-VLTI instrument with 4 beams. The combined use of this module together with the MIDI instrument is the project called APreS-MIDI. Such an instrument at the VLTI focus will have an unique and very strong astrophysical potential.
APreS-MIDI (APerture Synthesis in the MID-Infrared) instrument function is to recombine 4 telescope beams of the VLTI. Interference fringes are sampled in the pupil plane. The optical principle uses "image densification". It is perfectly adapted for reconstructing images by aperture synthesis at 10mm. This principle could be used for building a new generation 10mm instrument, but instead of making a totally new instrument, we propose the design of an optical module that can supply the current MIDI-VLTI instrument with 4 beams.
Micro-channel plate (MCP) based "Generation 2" image intensifiers are used for initial photon detection and amplification in modern photon counting detectors in astronomy. Input photons initially create photo-electrons in a photocathode. Each photo-electron is then amplified by the MCP or an MCP stack producing a cloud of electrons that are proximity focused onto an output anode. During the electron amplification process charge is stripped from the walls of the associated pore (or pores if an MCP stack is employed) and this needs to be replenished before full gain amplification of following events can take place. Charge depletion then provides the ultimate limitation to the brightness of a point source that can be observed. Experimental work has been undertaken to measure the effect of gain depression in intensified CCD detectors using intensifiers with both P20 and P46 phosphors. The results, along with a discussion on their relevance to detector dynamic range, will be presented.
MIDI is the Mid-Infrared interferometer for ESO's VLTI (Very Large Telescope Interferometer), which has been developed by a German-Dutch-French consortium [MPIA Heidelberg Germany, NOVA/ASTRON Dwingeloo Netherlands, Observatoire de Meudon France]. The initial aim of MIDI is to combine the beams from 2 telescopes in the 10 micron N-band with a spatial resolution of up to 10 milli-arcseconds and a maximum spectral resolution of 230. Modulation of the optical path difference can be done using piezo-driven mirrors at room temperature, but beam combination and detection of the interferometric signal has to be done at cryogenic temperatures due to the 'thermal' wavelength domain. The MIDI cold bench is therefore mounted inside a cryostat, cooled by means of a closed cycle cooler to about 40K for the cold optics and 8K for the detector.
The design of the cold optics has been kept as simple as possible, creating challenges such as preserving alignment from 295K to 40K and accessibility. This poster describes the realization of the cold optics, the alignment and test strategies and laboratory results.
The first science instrument for the Very Large Telescope Interferometer (VLTI), the Mid-infrared instrument MIDI, will be commissioned in November 2002 with anticipated first fringe during that commissioning run on the 40-cm Siderostats and the 8.2-meter Unit Telescopes. In this paper we describe scientific and technical observing modes (also referred to as observation procedures) developed for MIDI and discuss in detail how an observing run with the instrument is planned.
MIDI is built by a consortium lead by the Max Planck Institute for Astronomy (MPIA Heidelberg), with contributions from among others ASTRON (Dwingeloo, The Netherlands), Leiden Observatory, University of Amsterdam, Paris Observatory, University of Groningen, the Kiepenheuer-Institut fur Sonnenpysik at Freiburg, Thuringer Landessternwarte Tautenburg, and the Observatoire de la Cote d'Azur.
The mid-infrared interferometric instrument MIDI is currently undergoing testing in preparation for commissioning on the Very Large Telescope Interferometer VLTI at the end of this year 2002. It will perform interferometric observations over the 8 μm - 13 μm wavelength range, with a spatial resolution of 20 milliarcsec, a spectral resolution of up to 250, and an anticipated point source sensitivity of N = 4 mag or 1 Jy for self-fringe tracking, which will be the only observing mode during the first months of operation. We describe the layout of the instrument and the performance during laboratory tests, both for broadband and spectrally resolved observing modes. We also briefly outline the planned guaranteed time observations.
ESO's new Very Large Telescope will consist of four 8.2 m telescopes and three moveable 1.8 m telescopes. Light from these can be combined in the Very Large Telescope Interferometer (VLTI) providing milli-arcsecond resolution with high sensitivity. The VLTI will first operate in the infrared and will produce first fringes in 2001. MIDI is the VLTI instrument for interferometry in the mid-infrared (10 - 20 microns) and is under development by a German-Dutch- French consortium. The initial aim of MIDI is to combine the beams of two telescopes in the 10 micron `N-band' and to achieve spatial resolutions of 20 milli-arcseconds at a spectral resolution of 200 - 300. Modulation of the optical path difference can be done using piezo-driven mirrors at room temperature, but beam combination and detection of the interferometric signal has to be done at cryogenic temperatures due to the `thermal' wavelength domain. The MIDI cold bench is therefore mounted inside a cryostat, cooled by means of a closed cycle cooler to about 40 K for the cold optics and 8 K for the detector. This poster describes the design and implementation of the MIDI cold bench.
We describe principles, design and present status of MIDI, the mid-infrared interferometric instrument for the VLTI, which is planned to come into operation at the ESO Very Large Telescope Interferometer during the second half of 2001.