GRAVITY+: reducing non-common-path aberrations for sub-10 {\mu}as astrometric accuracy

Quentin Fournier; Guillaume Bourdarot; Frank Eisenhauer; Helmut Feuchtgruber; Dieter Lutz; Etienne Rosin; Stefan Gillessen; Reinhard Genzel; Taro Shimizu; Oliver Pfuhl; Felix Mang; Michael Hartl; Thomas Ott; Ekkehard Wieprecht; Vishaal Gopinath; Françoise Delplancke-Stroebele; Luis Esteras Otal; Felix Widmann; Sebastiano von Fellenberg; Pierre Bourget; Guy Perrin; Julien Woillez; Paulo Garcia; Sebastian Hönig; Laura Kreidberg; Jean-Baptiste Le Bouquin; Thibaut Paumard; Christian Straubmeier; for the GRAVITY+ Collaboration

arXiv · 2608.05751

GRAVITY+: reducing non-common-path aberrations for sub-10 {\mu}as astrometric accuracy

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Abstract

GRAVITY is a state-of-the-art instrument for near-infrared astrometric interferometry that routinely achieves astrometric accuracy of 30-100 microarcsecond in its phase-referenced dual-field mode. However, its fundamental limit is not yet reached, and can still be improved by several factors. In this paper, we focus on the effect of systematics, and in particular the effect of non-common path aberrations between the science channel and the metrology signal in the GRAVITY Fiber Coupler. Through comprehensive laboratory measurements using a dedicated fiber coupler replica and phase-shifting interferometry at 1908 nm, we have characterized these high-order wavefront errors with nanometer precision in the laboratory. We characterized on-sky the effect of these high-order wavefront imperfections on narrow-angle astrometry, using observations of the binary system GJ65. As part of the GRAVITY+ project, high-precision mirrors designed for nanometer-level surface quality, bringing an order of magnitude improvement over existing GRAVITY injection optics, are currently in production and will be installed in the fiber coupler units by the end of 2027. This upgrade is expected to enable astrometric accuracy at the sub-10 microarcsecond level in dual-field mode with integration times of just a few minutes.

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Quentin Fournier, Guillaume Bourdarot, Frank Eisenhauer, Helmut Feuchtgruber, Dieter Lutz, Etienne Rosin, Stefan Gillessen, Reinhard Genzel, Taro Shimizu, Oliver Pfuhl, Felix Mang, Michael Hartl, Thomas Ott, Ekkehard Wieprecht, Vishaal Gopinath, Françoise Delplancke-Stroebele, Luis Esteras Otal, Felix Widmann, Sebastiano von Fellenberg, Pierre Bourget, Guy Perrin, Julien Woillez, Paulo Garcia, Sebastian Hönig, Laura Kreidberg, Jean-Baptiste Le Bouquin, Thibaut Paumard, Christian Straubmeier, for the GRAVITY+ Collaboration. 2026-08-06. GRAVITY+: reducing non-common-path aberrations for sub-10 {\mu}as astrometric accuracy. https://arxiv.org/abs/2608.05751

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