Potential and sky coverage for off-axis fringe tracking in optical long baseline interferometry

Boskri, Abdelkarim; Petrov, R.; Halkouj, Thami El; Hadjara, M.; Leftley, James; Benkhaldoun, Z.; Cruzalèbes, P.; Ziad, Aziz; Carbillet, Marcel

doi:10.1093/mnras/stab1505

Cited by 4 publications

(6 citation statements)

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“…However, this scale ranges from 12 to 50 m at all major astronomical sites (Ziad 2016), and is about 22 m (Martinez et al 2010) in the atmosphere model of Paranal. This leads to an underestimation of the maxi- mum visibility in our calculations for large telescopes (Elhalkouj et al 2008;Boskri et al 2021), but does not affect much the visibility estimates for the comparably small ATs (Fig. 10).…”

Section: Atmospheric Conditions On Paranalmentioning

confidence: 74%

“…Furthermore, the outer scale of turbulence L 0 is assumed to be infinity (Buscher & Longair 2015), following the Kolmogorov model. A full treatment taking into account the effect and statistics of the outer scale of turbulence can be found in Boskri et al (2021). Elhalkouj et al (2008) considered two different scenarios for deriving the isopistonic angle error.…”

Section: Atmospheric Coherence Lossmentioning

confidence: 99%

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First light for GRAVITY Wide

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Allouche

Amorim

et al. 2022

A&A

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GRAVITY+ is the upgrade for GRAVITY and the Very Large Telescope Interferometer (VLTI) with wide-separation fringe tracking, new adaptive optics, and laser guide stars on all four 8 m Unit Telescopes (UTs) to enable ever-fainter, all-sky, high-contrast, milliarcsecond interferometry. Here we present the design and first results of the first phase of GRAVITY+, known as GRAVITY Wide. GRAVITY Wide combines the dual-beam capabilities of the VLTI and the GRAVITY instrument to increase the maximum separation between the science target and the reference star from 2 arcseconds with the 8 m UTs up to several 10 arcseconds, limited only by the Earth's turbulent atmosphere. This increases the sky-coverage of GRAVITY by two orders of magnitude, opening up milliarcsecond resolution observations of faint objects and, in particular, the extragalactic sky. The first observations in 2019 -2022 include the first infrared interferometry of two redshift z ∼ 2 quasars, interferometric imaging of the binary system HD 105913A, and repeat observations of multiple star systems in the Orion Trapezium Cluster. We find the coherence loss between the science object and fringe-tracking reference star well described by the turbulence of the Earth's atmosphere. We confirm that the larger apertures of the UTs result in higher visibilities for a given separation due to the broader overlap of the projected pupils on the sky and provide predictions for visibility loss as a function of separation to be used for future planning.

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Section: Atmospheric Conditions On Paranalmentioning

confidence: 74%

Section: Atmospheric Coherence Lossmentioning

confidence: 99%

First light for GRAVITY Wide

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Allouche

Amorim

et al. 2022

A&A

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“…Further gain can be obtained by an extension of the tracking band. Boskri et al [8] sensitivity estimates are based on a J+H+K band tracker assuming the Strehl ratios expected from the GRAVITY+ upgrade on UTs or the current NAOMI Adaptative Optics on ATs. Each band would be fed in a separate chip and the outputs of each chip would be analyzed without dispersion.…”

Section: A Very Broad Band Hft and Its Potential For Agns On The Vlti...mentioning

confidence: 99%

“…Despite its state-of-the-art design, control system, integrated optics chip and high performance Saphira detector, the GFT is not reaching the sensitivity limit that is achievable on the VLTI with the current technology. Boskri et al 2021 [8] show that the new generation hierarchical fringe tracker (HFT) proposed by [9] using the J, H and K bands should achieve K~15.9 on UTs and K~12.2 on ATs. These magnitudes are necessary to achieve, among other programs, the full potential of MATISSE for Young Stellar Objects studies as well as for the AGN program both with MATISSE and in the J and H bands.…”

Section: Introductionmentioning

confidence: 99%

“…− 1) measurements (4 measurements per baseline for each of the 𝑛 " spectral channels). At low flux, near the sensitivity limit of the fringe tracker, the readout noise from this relatively large number of measures that increases with the number of apertures is the limiting factor even with a very efficient detector like the Saphira as shown in [8]. Moreover, when the science instruments operate in different spectral bands than the FT, the rate of fringe jumps of one tracking wavelength generated by the FT are a key limiting factor for the frame time and hence the sensitivity with the science instrument, as abundantly illustrated by our GRA4MAT experience.…”

Section: Introductionmentioning

confidence: 99%

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Hierarchical Fringe Tracking, sky coverage and AGNs with the VLTI

Petrov

Allouche

Boskri

et al. 2022

Optical and Infrared Interferometry and Imaging VIII

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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.

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MATISSE, the VLTI mid-infrared imaging spectro-interferometer

López

Lagarde

Petrov

et al. 2022

A&A

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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 (AGN). Methods. The instrument is a spectro-interferometric imager in the transmission windows called L, M, and N, 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 in L&M bands, namely 30, 500, 1000 and 3400, and 30 and 220 in the N band, and it provides an angular resolution down to 3 mas for the shortest wavelengths. The MATISSE stand-alone sensitivity limits are 60 mJy in L and 300 mJy in N. 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.

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Potential and sky coverage for off-axis fringe tracking in optical long baseline interferometry

Cited by 4 publications

References 46 publications

First light for GRAVITY Wide

First light for GRAVITY Wide

Hierarchical Fringe Tracking, sky coverage and AGNs with the VLTI

MATISSE, the VLTI mid-infrared imaging spectro-interferometer

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