The Very Large Telescope Interferometer (VLTI) is currently the best infrastructure for long-baseline interferometry in particular in terms of sensitivity and accessibility to the general user. MATISSE, installed at the VLTI focus since end of 2017, belongs to the second generation instruments. MATISSE, the Multi AperTure mid-Infrared SpectroScopic Experiment, for the first time accesses high resolution imaging over a wide spectral domain of the mid-infrared. The instrument is a spectro-interferometric imager in the atmospheric transmission windows called L, M, and N, from 2.8 to 13.0 microns, and combines four optical beams from the VLTI’s unit or auxiliary telescopes. 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 flux, visibility, closure phase, wavelength differential visibility and phase, and aperture-synthesis imaging. MATISSE can operate as a stand alone instrument or with the GRA4MAT set-up employing the GRAVITY fringe tracking capabilities. The updated MATISSE performance are presented at the conference together with a selection of two front-line science topics explored since the start of the science operations in 2019. Finally we present the perspective and benefit of two technical improvements foreseen in the coming years: the MATISSE-Wide off-axis fringe tracking capability and new adaptive optics for the UTs in the context of the GRAVITY+ project.
Hierarchical Fringe Tracking (HFT) is a fringe tracking concept optimizing the sensitivity in optical long baseline by reducing to an absolute minimum the number of measurements used to correct the OPD fluctuations. By nature, the performances of an HFT do not decreases with the number of apertures of the interferometer and are set only by the flux delivered by the individual telescopes. This a critical feature for future interferometers with large number of apertures both for homodyne and heterodyne operation. Here we report the design and first optical bench tests of integrated optics HFT chips for a 4 telescopes interferometer such as the VLTI. These tests validate the HFT concept and confirm previous estimates that we could track accurately fringes on the VLTI up to nearly K~15.9 with the UTs and K~12.2 with the ATs with a J+H+K fringe tracker with one HFT chip per band. This is typically 2.5 magnitudes fainter than the best potential performance of the current ABCD fringe tracker in the K band. An active longitudinal and transverse chromatic dispersion correction allows the optimization of broad band fiber injections and instrumental contrast. We also present a preliminary evaluation of the potential of such a gain of sensitivity for the observations of AGNs with the VLTI.
We present the testbench aimed at integrating the GRAVITY+ adaptive optics GPAO. It consists of two independent elements, one reproducing the Coudé focus of the telescope, including the telescope deformable mirror mount (with its surface facing down), and one reproducing the Coudé room opto-mechanical environment, including a downwards-propagating beam, and the telescope mechanical interfaces in order to fit in the new GPAO wavefront sensor. We discuss in this paper the design of this bench and the solutions we adopted to keep the cost low, keep the design compact (allowing it to be fully contained in a 20 sqm clean room), and align the bench independently from the adaptive optics. We also discuss the features we have set in this bench.
SPICA-FT is part of the CHARA/SPICA instrument which combines a visible 6T fibered instrument (SPICAVIS) with a H-band 6T fringe sensor. SPICA-FT is a pairwise ABCD integrated optics combiner. The chip is installed in the MIRC-X instrument. The MIRC-X spectrograph could be fed either by the classical 6T fibered combiner or by the SPICA-FT integrated optics combiner. SPICA-FT also integrates a dedicated fringe tracking software, called the opd-controller communicating with the main delay line through a dedicated channel. We present the design of the integrated optics chip, its implementation in MIRC-X and the software architecture of the group-delay and phase-delay control loops. The final integrated optics chip and the software have been fully characterized in the laboratory. First on-sky tests of the integrated optics combiner began in 2020. We continue the on-sky tests of the whole system (combiner + software) in Spring and Summer 2022. We present the main results, and we deduce the preliminary performance of SPICA-FT.
With a possible angular resolution down to 0.1-0.2 millisecond of arc using the 330 m baselines and the access to the 600-900 nm spectral domain, the CHARA Array is ideally configured for focusing on precise and accurate fundamental parameters of stars. CHARA/SPICA (Stellar Parameters and Images with a Cophased Array) aims at performing a large survey of stars all over the Hertzsprung-Russell diagram. This survey will also study the effects of the different kinds of variability and surface structure on the reliability of the extracted fundamental parameters. New surface-brightness-colour relations will be extracted from this survey, for general purposes on distance determination and the characterization of faint stars. SPICA is made of a visible 6T fibered instrument and of a near-infrared fringe sensor. In this paper, we detail the science program and the main characteristics of SPICA-VIS. We present finally the initial performance obtained during the commissioning.
VERMILION is a VLTI visitor instrument project intended to extend the sensitivity and the spectral coverage of Optical Long Baseline Interferometry (OLBIn). It is based on a new concept of Fringe Tracker (VERMILIONFT) combined with a J band spectro-interferometer (VERMILION-J). The Fringe Tracker is the Adaptive Optics module specific to OLBIn that measures and corrects in real time the Optical Path Difference (OPD) perturbations introduced by the atmosphere and the interferometer, by providing a sensitivity gain of 2 to 3 magnitudes over all other state of the art fringe trackers. The J band spectro-interferometer will provide all interferometric measurements as a function of wavelength. In addition to a possible synergy with MATISSE, VERMILION-J, by observing at high spectral resolution many strong lines in J (Paβ-γ, HeII, TiO and other metallic monoxides), will cover several scientific topics, e.g. Exoplanets, YSOs, Binaries, Active Hot, Evolved stars, Asteroseismology, and also AGNs.
MATISSE, the VLTI 2nd generation spectro-interferometric L, M and N bands imager, has been commissioned from March 2018 to March 2020. It is open to the General User since April 2019. A complete analysis of its performances is given in this paper for MATISSE standalone (with UTs and ATs) and for the GRAVITY for MATISSE (GRA4MAT) mode (with ATs) where the GRAVITY fringe tracker is used to stabilize the fringes in MATISSE and hence improve its sensitivity and spectral coverage at high spectral resolution. This paper presents the key operation parameters of MATISSE and decomposes its performances in fundamental precision per spectral channel for all measurements and in broad band calibration errors on the accuracy of visibility and closure phase. It is intended to give the user a full description of the different errors that must be considered and weighted in the model fitting and image reconstruction. The first image reconstructions achieved by MATISSE are discussed. The performances demonstrated here in the full very broad spectral domain of MATISSE open a very large domain of scientific applications that includes but strongly expands quantitatively and qualitatively the initial science program of the first generation instrument MIDI and, combined with GRAVITY, offers an extremely powerful tool to characterize the temperature and composition of dusty and molecular components of YSOs, AGNs and evolved stars.
CHARA/SPICA (Stellar Parameters and Images with a Cophased Array) is currently being developed at Observatoire de la Cote d’Azur. It will be installed at the visible focus of the CHARA Array by the end of 2021. It has been designed to perform a large survey of fundamental stellar parameters with, in the possible cases, a detailed imaging of the surface or environment of stars. To reach the required precision and sensitivity, CHARA/SPICA combines a low spectral resolution mode R = 140 in the visible and single-mode fibers fed by the AO stages of CHARA. This setup generates additional needs before the interferometric combination: the compensation of atmospheric refraction and longitudinal dispersion, and the fringe stabilization. In this paper, we present the main features of the 6-telescopes fibered visible beam combiner (SPICA-VIS) together with the first laboratory and on-sky results of the fringe tracker (SPICA-FT). We describe also the new fringe-tracker simulator developed in parallel to SPICA-FT.
MATISSE is the second-generation mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric instrument will allow significant advances in various fundamental research fields: studying the planet-forming region of disks around young stellar objects, understanding the surface structures and mass loss phenomena affecting evolved stars, and probing the environments of black holes in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the spectral domain of current optical interferometers by offering the L and M bands in addition to the N band. This will open a wide wavelength domain, ranging from 2.8 to 13 μm, exploring angular scales as small as 3 mas (L band) / 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared imaging - closure-phase aperture-synthesis imaging - with the four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we remind the concept, the instrumental design, and the main features of MATISSE. We also describe the last months of preparation, the status of the instrument, which was shipped to Cerro Paranal on the site of the ESO Very Large Telescope in October 2017, and the expected schedule for the opening to the community. The instrument is currently in its Commissioning phase. A complementary dedicated article details the Commissioning results, which include the first performance estimates on sky.
MATISSE is the 2nd generation mid-infrared instrument designed to combine four VLTI telescopes in the L, M and N spectral bands. It’s commissioning in Paranal is in progress since March 2018 and should continue until the middle of 2019. Here we report, in June 2018, the commissioning plan, tools and the preliminary results of the first two commissioning runs in MATISSE that show that the instrument is already fully operational with a sensitivity well beyond its specification. The quality of the measurements, as they obtained by the current observing procedures and delivered by the current pipeline are already good enough for a broad range of science observations. However, our results remain quite preliminary and they will be quite substantially improved by the work in progress in instrument calibration, observing procedures optimization and data processing updates.
MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) is the spectro-interferometer for the VLTI of the European Southern Observatory (ESO), operating in the L-, M- and N- spectral bands, and combining up to four beams from the unit or the auxiliary telescopes (UTs or ATs). MATISSE will offer new breakthroughs in the study of circumstellar environments by allowing the mapping of the material distribution, the gas and essentially the dust. The instrument consists in a warm optical system (WOP) accepting four beams from the VLTI and relaying them after a spectral splitting to cold optical benches (COB) located in two separate cryostats, one in L-M- band, and one in N-band. The test plan of the complete instrument has been conducted at the Observatoire de la Côte d’Azur in order to confirm the compliance of the performance with the high-level requirements. MATISSE has successfully passed the Preliminary Acceptance in Europe the 12th September 2017. Following this result, ESO gave approval for the instrument to be shipped to Paranal. The Alignment, Integration and Verification phase was conducted until end of February 2018, at the end of which first observations on sky have been performed to test the operations with the VLTI and to obtain first stellar light. The two first runs of the commissioning followed, respectively in March and in May 2018. It has the goal to optimize the MATISSE-VLTI communication, the acquisition procedures and the interface parameters. The observations were performed on bright L-M- and N- stars, with four ATs located on short baselines and UTs. The limit magnitudes will be deduced.
This paper reports on the performance of the instrument measured in laboratory (results of test plan in Nice and AIV in Paranal) in terms of spectral coverage, dispersion laws and spectral resolutions, and transfer function analysis: instrumental contrast, visibility accuracy, accuracy of the differential phase, of the closure-phase and of the differential visibility. It also provides results of the first tests on sky and the planning of the on-going commissioning.
ESO is undertaking a large upgrade of the infrastructure on Cerro Paranal in order to integrate the 2nd generation of interferometric instruments Gravity and MATISSE, and increase its performance. This upgrade started mid 2014 with the construction of a service station for the Auxiliary Telescopes and will end with the implementation of the adaptive optics system for the Auxiliary telescope (NAOMI) in 2018. This upgrade has an impact on the infrastructure of the VLTI, as well as its sub-systems and scientific instruments.
We present in this paper the general formalism and data processing steps used in the MATISSE data reduction software, as it has been developed by the MATISSE consortium. The MATISSE instrument is the mid-infrared new generation interferometric instrument of the Very Large Telescope Interferometer (VLTI). It is a 2-in-1 instrument with 2 cryostats and 2 detectors: one 2k × 2k Rockwell Hawaii 2RG detector for L&M-bands, and one 1k × 1k Raytheon Aquarius detector for N-band, both read at high framerates, up to 30 frames per second. MATISSE is undergoing its first tests in laboratory today.
MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) is the spectro-interferometer for the VLTI of the European Southern Observatory, operating in near and mid-infrared, and combining up to four beams from the unit or the auxiliary telescopes. MATISSE will offer new breakthroughs in the study of circumstellar environments by allowing the multispectral mapping of the material distribution, the gas and essentially the dust.
The instrument consists in a warm optical system (WOP) accepting four optical beams and relaying them after a dichroic splitting (for the L and M- and N- spectral bands) to cold optical benches (COB) located in two separate cryostats. The Observatoire de la Côte d’Azur is in charge of the WOP providing the spectral band separation, optical path equalization and modulation, pupil positioning, beam anamorphosis, beam commutation, and calibration. NOVA-ASTRON is in charge of the COB providing the functions of beam selection, reduction of thermal background emission, spatial filtering, pupil transfer, photometry and interferometry splitting, additional beam anamorphosis, spectral filtering, polarization selection, image dispersion, and image combination. The Max Planck Institut für Radio Astronomie is in charge of the operation and performance validation of the two detectors, a HAWAII-2RG from Teledyne for the L- and M- bands and a Raytheon AQUARIUS for the N-band. Both detectors are provided by ESO. The Max Planck Institut für Astronomie is in charge of the electronics and the cryostats for which the requirements on space limitations and vibration stability resulted on very specific and stringent decisions on the design.
The integration and test of the COB: the two cryogenic systems, including the cold benches and the detectors, have been conducted at MPIA in parallel with the integration of the WOP at OCA. At the end of 2014, the complete instrument was integrated at OCA. Following this integration, a period of interface and alignment between the COB and the WOP took place resulting in the first interference fringes in the L-band during summer 2015 and the first interference fringes in the N-ban in March 2016.
After a period of optimization of both the instrument reliability and the environmental working conditions, the test plan is presently being conducted in order to evaluate the complete performance of the instrument and its compliance with the high-level requirements. The present paper gives the first results of the alignment, integration and test phase of the MATISSE instrument.
MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) is the next generation spectro-interferometer at the European Southern Observatory VLTI operating in the spectral bands L, M and N, and combining four beams from the unit and auxiliary telescopes. MATISSE is now fully integrated at the Observatoire de la Cˆote d’Azur in Nice (France), and has entered very recently its testing phase in laboratory. This paper summarizes the equations describing the MATISSE signal and the associated sources of noise. The specifications and the expected performances of the instrument are then evaluated taking into account the current characteristics of the instrument and the VLTI infrastructure, including transmission and contrast degradation budgets. In addition, we present the different MATISSE simulation tools that will be made available to the future users.
MATISSE is the second-generation mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric instrument will allow significant advances by opening new avenues in various fundamental research fields: studying the planet-forming region of disks around young stellar objects, understanding the surface structures and mass loss phenomena affecting evolved stars, and probing the environments of black holes in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the spectral domain of current optical interferometers by offering the L and M bands in addition to the N band. This will open a wide wavelength domain, ranging from 2.8 to 13 μm, exploring angular scales as small as 3 mas (L band) / 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared imaging - closure-phase aperture-synthesis imaging - with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE will offer a spectral resolution range from R ∼ 30 to R ∼ 5000. Here, we present one of the main science objectives, the study of protoplanetary disks, that has driven the instrument design and motivated several VLTI upgrades (GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performances. We also discuss the current status of the MATISSE instrument, which is entering its testing phase, and the foreseen schedule for the next two years that will lead to the first light at Paranal.
We propose a new high dynamic imaging concept for the detection and characterization of extra-solar planets. DIFFRACT standing for DIFFerential Remapped Aperture Coronagraphic Telescope, uses a Wollaston prism to split the entrance pupil into two exit pupils. These exit pupils are then remapped with 2 apertures lenses of different diameters resulting in two separate rescaled focal images of the same star. Since the angular separation of a putative exoplanet orbiting around the star is independent of the angular resolution of the remapped output pupils they appear at the same linear location in the resulting images that differ in resolution proportional to the exit pupil sizes.
Exoplanet detection is obtained by numerically rescaling the images at the same angular resolution and substracting them, so that, under aberration and photon noise free conditions the planet twin images appear as two positive and negative Airy patterns. In real conditions however and depending on the exoplanet separation normalized to the angular resolution of the input telescope detection performances depend strongly on the adaptive optics performances and the collecting surface of the telescope. In this study we present the formal expression of DIFFRACT optics concept with a complet set of numerical experiments to
estimate the performances of the concept under real observing conditions including instrument and adaptive optics corrections.
The hypertelescope construction initiated in the Southern Alps (Labeyrie et al., this conference) has
provided some preliminary operating experience indicating that larger versions, up to perhaps
1200m, are probably feasible at suitable sites. The Arecibo-like architecture of such instruments
does not require the large mount and dome which dominate the cost of a 40m ELT. For the same
cost, an "Extremely Large Hyper Telescope” ( ELHyT) may therefore have a larger collecting area.
It may thus in principle reach higher limiting magnitudes, both for seeing-limited and, if equipped
with a Laser Guide Star and adaptive phasing, for high-resolution imaging with gain as the size ratio,
i.e. about 30 with respect to a 40m ELT. Like the radio arrays of antennas, such instruments can be
grown progressively. Also, they can be up-graded with several focal gondolas, independently
tracking different sources. Candidate sites have been identified in the Himalaya and the Andes. We
describe several design options and compare the science achievable for both instruments, ELTs and
ELHyTs. The broad science addressed by an ELHyT covers stellar chromospheres, transiting exoplanets
and those requiring a high dynamic range, achieved by array apodization or coronagraphy.
With a Laser Guide Star, it extends to faint compact sources beyond the limits of telescopes having a
smaller collecting area, supernovae, active galactic nuclei, gamma ray bursts. The sparse content of
remote galaxies seen in the Hubble Deep Field appears compatible with the crowding limitations of
an ELHyT having 1000 apertures.
A. Labeyrie, F. Allouche, D. Mourard, F. Bolgar, R. Chakraborty, J. Maillot, N. Palitzyne, J. R. Poletti, J.-P. Rochaix, R. Prud'homme, A. Rondi, M. Roussel, A. Surya
For information-rich direct images at high resolution, hypertelescopes combine light from a sparse array of
many subapertures, using pupil densification. Among the possible architectures, the Arecibo-like spherical class
has fixed mirrors arrayed as elements of a common spherical locus, matching approximately the natural curvature
of a crater or valley. A focal gondola suspended on the focal sphere, is tracking the primary star image, and several
more can be added for independent observations of di.erent sources. Since no delay lines are needed, hundred of
mirrors can be used for reaching the theoretical information gain with respect to fewer apertures. The aperture
size of such instruments may range from 50 to perhaps 1200m at available terrestrial sites. As an example of their
broad science capabilities, we have simulated the resolved and spectro-imaging- of an exoplanet transiting across
the disk of its parent star, achievable with adaptive optics. Faint cosmological sources may also become observable
if a Laser Guide Star can be fitted. We describe the current construction and in situ opto-mechanical testing
of a 57m hypertelescope, later expandable to 200 with 100 or more sub-apertures. The preliminary operating
experience gained in a year, without stellar fringes yet, indicates the likely feasibility of larger versions at suitable
sites. Labeyrie et al., (this conference) discuss an "Extremely Large Hypertelescope" (ELHyT) having 1200m
sparse aperture and, at similar cost, a larger collection area and higher limiting magnitude than a 40m ELT.
In 1996, Jean Gay and Yves Rabbia presented their Achromatic Interferential Coronagraph (AIC) for detecting
and imaging faint companions (ultimately exoplanets) in the neighboring of a star. As presented then,
the Michleson-like Interferometer configuration of the AIC hardens its insertion into an existing (coaxial) optical
train, the output beam of the AIC being delivered at right angle from the input beam. To overcome this, they
reconfigured the AIC into a compact and fully axial coronagraph, the CIAXE, which main feature consists of
using two thick lenses machined in the same optical material. For the CIAXE to deliver the output beam along
the same axis as the input beam, the two lenses are coaxially disposed on the optical axis and are separated, at
their common spherical contact surface by a thin air gap acting like a beam splitter. We have set up a laboratory
experiment aiming at validating the principle of the concept. Our first step was to equalize the thicknesses of the
two lenses, so as to make zero the optical path difference between both arms. For this, the (residual) value of the
OPD has been evaluated and then the lenses have been re-machined so as to decrease as far as technologically
possible, the thicknesses mismatch. As a second step, a micro-controlled rotation around the common curvature
center of the spherical surfaces of the lenses is applied. This allows a fine tuning of the residual OPD at the
required accuracy level. Are presented here test bench, steps and results.
For the detection and direct imaging of exoplanets, when the intensity ratio between a star and its orbiting
planet can largely exceed 106, coronagraphic methods are mandatory. In 1996, a concept of achromatic interferocoronagraph
(AIC) was presented by J. Gay and Y. Rabbia for the detection of very faint stellar companions,
such as exoplanets. In an earlier paper, we presented a modified version of the AIC permitting to determine the
relative position of these faint companions with respect to the parent star, a problem unsolved in the original
design of the AIC. Our modification lied in the use of cylindrical lens doublets as field rotator. By placing two
of them in one arm of the interferometric set-up of AIC, we destroyed the axis of symmetry induced by the
AIC's original design. Our theoretical study, along with the numerical computations, presented then, and the
preliminary test bench results aiming at validating the cylindrical lens doublet field rotation capability, presented
in this paper, show that the axis of symmetry is destroyed when one of the cylindrical doublets is rotated around
the optic axis.
In 2004, our group proposed IRAN, an alternative beam-combination technique to the so-called hypertelescope
imaging method introduced by Labeyrie in the 1990s. We have recently set up a laboratory experiment
aiming at validating our image densification approach instead of the pupil densification scheme of Labeyrie.
In our experiment, seven sub-apertures illuminated by laser sources are recombined using the IRAN scheme.
The validation of the IRAN recombination consists basically in retrieving the point-spread intensity distribution
(PSID), demonstrating the conservation of the object-image convolution relation. We will introduce IRAN,
compare it to the hyper-telescope, and present the experimental results that we obtained.
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