Radial velocity follow-up of \textit{Gaia} astrometric substellar companions: six confirmed brown dwarfs and 13 impostor binaries
Abstract
With microarcsecond precision, \textit{Gaia} has made the astrometric discovery of substellar companions feasible. However, follow-up observations are needed to check on orbital solutions and rule out astrophysical false positives. We validate and characterise a sample of 20 \textit{Gaia} Data Release 3 (DR3) astrometric candidates for substellar companions, with the dual goal of identifying false positives and deriving robust physical parameters for genuine companions. We performed high-resolution spectroscopy using FIES, NIRPS, and NEID at the Nordic Optical Telescope, the ESO 3.6m telescope, and the WIYN Telescope, respectively. Double-lined spectroscopic binaries were identified as false positives, and surviving systems were characterised through joint \textit{Gaia} astrometry and radial velocity modelling. Thirteen of the candidates proved to be near-twin binary stars for which the astrometric motion of the center of light is small enough to mimic that of a single star in response to a substellar companion. We confirm that six companions are brown dwarfs with masses in the range ∼26--68 MJup, two of them for the first time. In contrast to earlier studies of lower-mass \textit{Gaia} candidates, we find that the astrometric orbital solutions are generally reliable to within the stated uncertainties.
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BibTeX
@misc{marcussen2026radial,
title = {{Radial velocity follow-up of \textitGaia astrometric substellar companions: six confirmed brown dwarfs and 13 impostor binaries}},
author = {Marcus L. Marcussen and Simon H. Albrecht and Kamil K. Kalinowski and Joshua N. Winn and Guðmundur Stefánsson and Jens Reersted Larsen and Julie Gadeberg and Evan Fitzmaurice and Kevin Schlaufman and Suvrath Mahadevan},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.08590},
eprint = {2609.08590},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.08590},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Radial velocity follow-up of \textit{Gaia} astrometric substellar companions: six confirmed brown dwarfs and 13 impostor binaries
AU - Marcus L. Marcussen
AU - Simon H. Albrecht
AU - Kamil K. Kalinowski
AU - Joshua N. Winn
AU - Guðmundur Stefánsson
AU - Jens Reersted Larsen
AU - Julie Gadeberg
AU - Evan Fitzmaurice
AU - Kevin Schlaufman
AU - Suvrath Mahadevan
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2609.08590
UR - https://arxiv.org/abs/2609.08590
AB - With microarcsecond precision, \textit{Gaia} has made the astrometric discovery of substellar companions feasible. However, follow-up observations are needed to check on orbital solutions and rule out astrophysical false positives. We validate and characterise a sample of 20 \textit{Gaia} Data Release 3 (DR3) astrometric candidates for substellar companions, with the dual goal of identifying false positives and deriving robust physical parameters for genuine companions. We performed high-resolution spectroscopy using FIES, NIRPS, and NEID at the Nordic Optical Telescope, the ESO 3.6m telescope, and the WIYN Telescope, respectively. Double-lined spectroscopic binaries were identified as false positives, and surviving systems were characterised through joint \textit{Gaia} astrometry and radial velocity modelling. Thirteen of the candidates proved to be near-twin binary stars for which the astrometric motion of the center of light is small enough to mimic that of a single star in response to a substellar companion. We confirm that six companions are brown dwarfs with masses in the range ∼26--68 M_Jup, two of them for the first time. In contrast to earlier studies of lower-mass \textit{Gaia} candidates, we find that the astrometric orbital solutions are generally reliable to within the stated uncertainties.
ER -