GRAVITY for MATISSE

Improving the MATISSE performance with the GRAVITY fringe tracker

¹ ESO Headquarters, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
e-mail: jwoillez@eso.org
² Université Côte d’Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Bd. de l'Observatoire, CS 34229, 06304 Nice cedex 4, France
e-mail: romain.petrov@unice.fr
³ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching bei München, Germany
⁴ ESO Vitacura, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
⁵ Leiden Observatory, Huygens Laboratory, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁶ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁷ HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly Observatory, Konkoly-Thege Miklós út 15–17, 1121 Budapest, Hungary

Received: 23 February 2024
Accepted: 17 May 2024

Abstract

Context. MATISSE, the mid-infrared spectro-imaging instrument of VLTI, was designed to deliver its designed performance when paired with an external second-generation fringe tracker. Science observations started in 2019, demonstrating imaging capabilities and faint science target observations. Now, the GRAVITY fringe tracker stabilises the MATISSE fringes, which allows the use of all spectroscopic modes and improves sensitivity and data accuracy.

Aims. We present how the MATISSE and GRAVITY instruments were adapted to make the GRAVITY fringe tracker work with MATISSE, under the umbrella of the aptly named GRA4MAT project, led by ESO in collaboration with the two instrument consortia.

Methods. We detail the software modifications needed to implement an acquisition and observing sequence specific to GRA4MAT, including simultaneous fringe tracking and chopping and a narrow off-axis capability inspired by the Galactic Centre and exoplanet capability of GRAVITY. We explain the modified data collection and reduction processes. We show how we leveraged the recent fringe tracker upgrade to implement features specific to its use with MATISSE, for example mitigation of fringe jumps with an improved group delay control, and simultaneous fringe tracking and chopping with a new state machine.

Results. We successfully demonstrate significant improvements to the MATISSE instrument. Observations can now be performed at higher spectral resolutions of up to R ~ 3300 and across the full LM bands at once. Long detector integration times, made possible with stabilised fringes, have improved the LM-band sensitivity by a factor of 10. Low flux biases in coherently reduced N-band data have been eliminated. The L-band transfer function is now higher and more stable. We finally illustrate the scientific potential of GRA4MAT with a preview of the first exoplanet observation made by MATISSE on β Pictoris b.