NOTT (formerly Hi-5) is the L’-band (3.5-4.0μm) nulling interferometer of Asgard, an instrument suite in preparation for the VLTI visitor focus. The primary scientific objectives of NOTT include characterizing (i) young planetary systems near the snow line, a critical region for giant planet formation, and (ii) nearby mainsequence stars close to the habitable zone, with a focus on detecting exozodiacal dust that could obscure Earthlike planets. In 2023-2024, the final warm optics have been procured and assembled in a new laboratory at KU Leuven. First fringes and null measurements were obtained using a Gallium Lanthanum Sulfide (GLS) photonic chip that was also tested at cryogenic temperatures. In this paper, we present an overall update of the NOTT project with a particular focus on the cold mechanical design, the first results in the laboratory with the final NOTT warm optics, and the ongoing Asgard integration activities. We also report on other ongoing activities such as the characterization of the photonic chip (GLS, LiNbO3, SiO), the development of the exoplanet science case, the design of the dispersion control module, and the progress with the self-calibration data reduction software.
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.
We report on observations of circumstellar disks around young stars that have been obtained with the MIDI instrument, which is mounted on the VLT Interferometer and operates in the 10 μm atmospheric window. The maximum spatial resolution of 5 milli-arcsec corresponds to sub-AU scales at the distance to nearby star formation regions. Thus, we can study the disks on the spatial scales at which important processes occur, such as accretion, dust processing, and planet formation. The main results obtained so far can be summarized as follows: 1. The measured interferometric visibilities are in good qualitative agreement with those predicted by models of circumstellar disks. In particular, a predicted correlation between the strength of the far-infrared excess and the spatial structure of the disk is confirmed by direct measurements; 2. In several objects strong evidence for deviations from circular symmetry is present, indicating that an inclined disk is indeed the dominant component seen in the mid-infrared; 3. The dust properties are not uniform over the disk, but are instead a strong function of distance to the central star. The dust in the innermost disk regions is observed to be more "processed" than the dust further out, both in Herbig Ae star disks and in those around T Tauri stars.
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.
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