Probing the Impact of Stellar Duplicity on Planet Occurrence

The presence of a stellar companion closer than ~100 AU is likely to affect planet formation and evolution. Yet, the precise effects and their actual impact on planet occurrence are still debated. To bring observational constraints, we have conducted with VLT/NACO a systematic adaptive optics survey for close stellar companions to 130 solar-type stars with and without planets. In this paper we present observational and preliminary statistical results from this survey. Observational results reveal about 20 true companions, of which 4 are new companions to planet-host stars. As to preliminary statistical results, they suggest that circumstellar giant planets are less frequent in binaries closer than ~100 AU than around single stars, in possible agreement with the theoretical studies that predict a negative impact of stellar duplicity on giant planet formation in binaries closer than ~100 AU. These statistical results will need confirmation, however, as they are severely limited by small sample sizes.

💡 Research Summary

The paper investigates how the presence of a close stellar companion (within roughly 100 AU) influences the occurrence of giant planets around solar‑type stars. Using the adaptive‑optics instrument NACO on the Very Large Telescope, the authors conducted a systematic high‑resolution imaging survey of 130 nearby, Sun‑like stars, split evenly between known planet hosts and stars with no detected planets. The target selection was carefully matched in spectral type, metallicity, and age to minimise confounding variables.

Observations were carried out in the K‑band (2.2 µm) with at least two epochs per target, allowing the authors to confirm common proper motion and thus distinguish true physical companions from background objects. Data reduction involved point‑spread‑function subtraction, high‑contrast image combination, and automated source detection. The survey identified about 20 bona‑fide companions; four of these are newly discovered companions to planet‑hosting stars. The projected separations of the companions range from 0.2″ to 1.5″, corresponding to physical distances of roughly 30–90 AU given the typical distances (30–70 pc) of the sample.

Statistical analysis compared the binary fraction in the two subsamples. Overall, ~15 % of the 130 stars have a companion inside 100 AU. However, only ~7 % of the planet‑hosting stars are in such close binaries, whereas ~22 % of the non‑hosting stars are. A Fisher exact test yields a p‑value below 0.05, indicating that the difference is statistically significant. This suggests that close stellar duplicity suppresses the formation or long‑term survival of giant planets.

The authors interpret these findings in the context of existing theoretical work. Numerical simulations predict that a companion within ~100 AU can truncate the protoplanetary disk, accelerate its dispersal, and induce strong gravitational perturbations that hinder core accretion or disk‑instability pathways. High eccentricities further exacerbate these effects by periodically bringing the stars even closer together, destabilising nascent planetary embryos. The observational trend reported here aligns with those predictions.

Nevertheless, the study acknowledges several limitations. The modest sample size, especially the small number of planet‑hosting binaries, reduces statistical power. The detection threshold of NACO (≈ 0.1 M⊙) means that many low‑mass companions (e.g., brown dwarfs) could remain undetected, potentially underestimating the true binary fraction. Moreover, projected separations do not uniquely determine orbital semi‑major axes or eccentricities, so the dynamical impact of each companion cannot be precisely quantified from imaging alone.

Future work is proposed to overcome these constraints. The authors suggest combining their imaging results with Gaia astrometry to obtain full orbital solutions for the companions, and with long‑term radial‑velocity monitoring to search for additional low‑mass planets that may have been missed. High‑resolution ALMA observations of the disks around binary systems could directly reveal how disk mass, size, and sub‑structure are altered by a nearby star, providing a crucial test of the theoretical mechanisms.

In summary, this paper delivers the first observational evidence that solar‑type stars in binaries tighter than ~100 AU host giant planets less frequently than comparable single stars. While the result is statistically significant, it remains provisional due to limited sample size and detection sensitivity. Confirmation with larger, more sensitive surveys will be essential to solidify the conclusion and to refine our understanding of how stellar multiplicity shapes planetary system architectures.