Mass-dependent multiplicity fraction in low mass stars revealed by Gaia astrometry
Abstract
Stellar multiplicity at different orbital periods is probed by different techniques: radial velocities at the shortest periods, direct imaging at the longest, and astrometry in between. Gaia DR3 provides unprecedented astrometric information to constrain binary populations with periods of tens to thousands of days. Beyond the small fraction of direct orbit solutions, Gaia publishes coarser astrometric diagnostics for all objects, such as on-sky accelerations, jerks, or the single-star goodness-of-fit measure, RUWE. We show that these diagnostics together are sensitive to a far wider range of orbital periods than orbit solutions alone. Built on the Gaiamock emulator, we develop a forward-modelling framework to constrain rates of multiplicity from Gaia data, using all astrometric solution types. We apply this framework to 366 027 primaries of $0.2−−0.75\,M_\odot$ between $50$ and $200$ pc, including vastly more M-dwarfs than previous multiplicity studies. For fiducial models of the period and mass-ratio distributions, the inferred multiplicity fraction is approximately constant at ∼45% from the solar-type regime down to 0.4 M⊙, only then dropping to ∼15% by 0.2 M⊙. This mass-multiplicity relationship revises the conventional picture of a monotonically rising mass--multiplicity relation, and aligns the upper M-dwarf regime with solar-type stars rather than placing it on a continuous decline.
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BibTeX
@misc{pennell2026massdependent,
title = {{Mass-dependent multiplicity fraction in low mass stars revealed by Gaia astrometry}},
author = {Ben Pennell and Hans-Walter Rix and Kareem El-Badry and Sahar Shahaf and Johanna Müller-Horn and Jiadong Li},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.01822},
eprint = {2609.01822},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.01822},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Mass-dependent multiplicity fraction in low mass stars revealed by Gaia astrometry
AU - Ben Pennell
AU - Hans-Walter Rix
AU - Kareem El-Badry
AU - Sahar Shahaf
AU - Johanna Müller-Horn
AU - Jiadong Li
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.01822
UR - https://arxiv.org/abs/2609.01822
AB - Stellar multiplicity at different orbital periods is probed by different techniques: radial velocities at the shortest periods, direct imaging at the longest, and astrometry in between. Gaia DR3 provides unprecedented astrometric information to constrain binary populations with periods of tens to thousands of days. Beyond the small fraction of direct orbit solutions, Gaia publishes coarser astrometric diagnostics for all objects, such as on-sky accelerations, jerks, or the single-star goodness-of-fit measure, RUWE. We show that these diagnostics together are sensitive to a far wider range of orbital periods than orbit solutions alone. Built on the Gaiamock emulator, we develop a forward-modelling framework to constrain rates of multiplicity from Gaia data, using all astrometric solution types. We apply this framework to 366 027 primaries of $0.2−−0.75\,M_\odot$ between $50$ and $200$ pc, including vastly more M-dwarfs than previous multiplicity studies. For fiducial models of the period and mass-ratio distributions, the inferred multiplicity fraction is approximately constant at ∼45% from the solar-type regime down to 0.4 M_⊙, only then dropping to ∼15% by 0.2 M_⊙. This mass-multiplicity relationship revises the conventional picture of a monotonically rising mass--multiplicity relation, and aligns the upper M-dwarf regime with solar-type stars rather than placing it on a continuous decline.
ER -