Exomoon search with VLTI/GRAVITY around the substellar companion HD 206893 B
Abstract
Direct astrometric detection of exomoons remains unexplored. This study presents the first application of high-precision astrometry to search for exomoons around substellar companions. We investigate whether the orbital motion of the companion HD 206893 B exhibits astrometric residuals consistent with the gravitational influence of an exomoon or binary planet. Using the VLTI/GRAVITY instrument, we monitored the astrometric positions of HD 206893 B and c across both short (days to months) and long (yearly) timescales. This enabled us to isolate potential residual wobbles in the motion of component B attributable to an orbiting moon. Our analysis reveals tentative astrometric residuals in the HD 206893 B orbit. If interpreted as an exomoon signature, these residuals correspond to a candidate (HD 206893 B I) with an orbital period of approximately 0.76 years and a mass of 0.4 Jupiter masses. However, the origin of these residuals remains ambiguous and could be due to systematics. Complementing the astrometry, our analysis of GRAVITY spectroscopy for HD 206893 B confirms a clear detection of water, but no CO is found using cross-correlation. We also find that AF Lep b, and Pic b are the best short-term candidates to look for moons with GRAVITY+. Our observations demonstrate the transformative potential of high-precision astrometry in the search for exomoons, and proves the feasibility of the technique to detect moons with masses lower than Jupiter and potentially down to less than Neptune in optimistic cases. Crucially, further high-precision astrometric observations with VLTI/GRAVITY are essential to verify the reality and nature of this signal and attempt this technique on a variety of planetary systems.
Cite
@article{arxiv.2511.20091,
title = {Exomoon search with VLTI/GRAVITY around the substellar companion HD 206893 B},
author = {Q. Kral and J. Wang and J. Kammerer and S. Lacour and M. Malin and T. Winterhalder and B. Charnay and C. Perrot and P. Huet and R. Abuter and A. Amorim and W. O. Balmer and M. Benisty and J. -P. Berger and H. Beust and S. Blunt and A. Boccaletti and M. Bonnefoy and H. Bonnet and M. S. Bordoni and G. Bourdarot and W. Brandner and F. Cantalloube and P. Caselli and G. Chauvin and A. Chavez and A. Chomez and E. Choquet and V. Christiaens and Y. Clénet and V. Coudé du Foresto and A. Cridland and R. Davies and R. Dembet and J. Dexter and A. Drescher and G. Duvert and A. Eckart and F. Eisenhauer and N. M. Förster Schreiber and P. Garcia and R. Garcia Lopez and T. Gardner and E. Gendron and R. Genzel and S. Gillessen and J. H. Girard and S. Grant and X. Haubois and Th. Henning and S. Hinkley and S. Hippler and M. Houllé and Z. Hubert and L. Jocou and M. Keppler and P. Kervella and L. Kreidberg and N. T. Kurtovic and A. -M. Lagrange and V. Lapeyrère and J. -B. Le Bouquin and D. Lutz and A. -L. Maire and F. Mang and G. -D. Marleau and A. Mérand and P. Mollière and J. D. Monnier and C. Mordasini and D. Mouillet and E. Nasedkin and M. Nowak and T. Ott and G. P. P. L. Otten and C. Paladini and T. Paumard and K. Perraut and G. Perrin and O. Pfuhl and N. Pourré and L. Pueyo and D. C. Ribeiro and E. Rickman and Z. Rustamkulov and J. Shangguan and T. Shimizu and D. Sing and J. Stadler and T. Stolker and O. Straub and C. Straubmeier and E. Sturm and L. J. Tacconi and A. Vigan and F. Vincent and S. D. von Fellenberg and F. Widmann and J. Woillez and S. Yazici and the GRAVITY Collaboration and K. Abd El Dayem and N. Aimar and A. Berdeu and C. Correia and D. Defrère and M. Fabricius and H. Feuchtgruber and A. Foschi and S. F. Hönig and S. Joharle and R. Laugier and O. Lai and J. Leftley and B. Lopez and F. Millour and M. Montargès and N. Morujão and H. Nowacki and J. Osorno and R. Petrov and P. O. Petrucci and S. Rabien and S. Robbe-Dubois and M. Sadun Bordoni and J. Sánchez Bermúdez and D. Santos and J. Sauter and J. Scigliuto and F. Soulez and M. Subroweit and C. Sykes and the GRAVITY+ Collaboration},
journal= {arXiv preprint arXiv:2511.20091},
year = {2026}
}
Comments
accepted for publication in A&A