The GRAVITY fringe tracker

Abstract

The GRAVITY instrument has been commissioned on the VLTI during 2016 and is now available to the astronomical community. It is the first optical interferometer capable of observing sources as faint as magnitude 19 in K-band. This is possible thanks to the fringe tracker which compensates the differential piston based on measurements of a brighter off-axis astronomical reference source. The goal of this paper is to consign the main developments made in the context of the GRAVITY fringe tracker. This could serve as basis for future fringe tracking systems. The paper therefore covers all aspects of the fringe tracker, from hardware, to control software and on-sky observations. Special emphasis is placed on the interaction between the group delay controller and the phase delay controller. The group delay control loop is a simple but robust integrator. The phase delay controller is a state-space control loop based on an auto-regressive representation of the atmospheric and vibrational perturbations. A Kalman filter provides optimal determination of the state of the system. The fringe tracker shows good tracking performance on sources with coherent K magnitudes of 11 on the UTs and 9.5 on the ATs. It can track fringes with an SNR level of 1.5 per DIT, limited by photon and background noises. On the ATs, during good seeing conditions, the optical path delay residuals can be as low as 75 nm root mean square. On the UTs, the performance is limited to around 250 nm because of structural vibrations.

Published in A&A. 18 pages

References in corpus (9)

• Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole
• First Light for GRAVITY: Phase Referencing Optical Interferometry for the Very Large Telescope Interferometer
• Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA*
• Interferometric data reduction with AMBER/VLTI.Principle,estimators and illustration
• Spatially resolved rotation of the broad-line region of a quasar at sub-parsec scale
• Reaching micro-arcsecond astrometry with long baseline optical interferometry; application to the GRAVITY instrument
• First result with AMBER+FINITO on the VLTI: The high-precision angular diameter of V3879 Sgr
• Comparison of fringe-tracking algorithms for single-mode near-infrared long-baseline interferometers
• AGILIS: Agile Guided Interferometer for Longbaseline Imaging Synthesis - Demonstration and concepts of reconfigurable optical imaging interferometers

Cited by in corpus (41)

• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
• Peering into the formation history of beta Pictoris b with VLTI/GRAVITY long baseline interferometry
• Constraining the Nature of the PDS 70 Protoplanets with VLTI/GRAVITY
• Direct confirmation of the radial-velocity planet $\beta$ Pic c
• An image of the dust sublimation region in the nucleus of NGC 1068
• The mass of Beta Pictoris c from Beta Pictoris b orbital motion
• The spatially resolved broad line region of IRAS 09149-6206
• The resolved size and structure of hot dust in the immediate vicinity of AGN
• Direct discovery of the inner exoplanet in the HD206893 system. Evidence for deuterium burning in a planetary-mass companion
• The GRAVITY Young Stellar Object survey -- I. Probing the disks of Herbig Ae/Be stars in terrestrial orbits
• The GRAVITY Young Stellar Object survey. VII. The inner dusty disks of T Tauri stars
• Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY
• NAOMI: the adaptive optics system of the Auxiliary Telescopes of the VLTI
• First Light for GRAVITY Wide: Large Separation Fringe Tracking for the Very Large Telescope Interferometer
• The cool brown dwarf Gliese 229 B is a close binary
• Asgard/NOTT: L-band nulling interferometry at the VLTI I. Simulating the expected high-contrast performance
• The GRAVITY young stellar object survey -- XI. Probing the inner disk and magnetospheric accretion region of CI Tau
• Combining Gaia and GRAVITY: Characterising five new Directly Detected Substellar Companions
• Resolving the Hot Dust Disk of ESO323-G77
• VLTI/GRAVITY Observations and Characterization of the Brown Dwarf Companion HD 72946 B
• Increasing the achievable contrast of infrared interferometry with an error correlation model
• The GRAVITY Young Stellar Object survey VIII. Gas and dust faint inner rings in the hybrid disk of HD141569
• Mid-infrared evidence for iron-rich dust in the multi-ringed inner disk of HD 144432
• Potential and sky coverage for off-axis fringe tracking in optical long baseline interferometry
• A catalogue of dual-field interferometric binary calibrators
• Compensation of differential dispersion: application to multiband stellar interferometry
• GRAVITY for MATISSE -- Improving the MATISSE performance with the GRAVITY fringe tracker
• Single-mode waveguides for GRAVITY II. Single-mode fibers and Fiber Control Unit
• Integrated turbulence parameters' estimation from NAOMI adaptive optics telemetry data
• Detecting planetary mass companions near the water frost-line using JWST interferometry
• Infrared interferometry to spatially and spectrally resolve jets in X-ray binaries
• The GRAVITY young stellar object survey XIV : Investigating the magnetospheric accretion-ejection processes in S CrA N
• High-contrast detection of exoplanets with a kernel-nuller at the VLTI
• Observations of Microlensed Images with Dual-field Interferometry: On-sky Demonstration and Prospects
• The mid-infrared spectrum of $\beta$ Pictoris b. First VLTI/MATISSE interferometric observations of an exoplanet
• Hot exozodiacal dust around Fomalhaut: The MATISSE perspective
• YSES 2b is a background star: Differential astrometric M-dwarf measurements in time
• Probing inner and outer disk misalignments in transition disks
• VLTI Unit Telescope coudé train vibration control upgrade for GRAVITY+
• A preliminary exploration of the effects of baseline length for the LIFE space mission
• Interferometric Detection and Orbit Modeling of the Subcomponent in the Hot-dust System $\kappa$ Tuc A: A Low-mass Star on an Eccentric Orbit in a Hierarchical-quintuple System