[Paper Review] Properties of planets in binary systems. The role of binary separation

S. Desidera, M. Barbieri|ArXiv.org|Oct 20, 2006

Stellar, planetary, and galactic studiesPhysics and Astronomy84 references128 citations

TL;DR

This study analyzes the statistical properties of exoplanets in binary star systems, focusing on how binary separation influences planetary characteristics. Using an updated sample of planets in binaries, it finds that massive short-period planets are predominantly found in tight binaries (separations < 100–300 AU), while planets in wide binaries are statistically similar to those around single stars, except for a possible excess of high-eccentricity planets.

ABSTRACT

The statistical properties of planets in binaries were investigated. Any difference to planets orbiting single stars can shed light on the formation and evolution of planetary systems. As planets were found around components of binaries with very different separation and mass ratio, it is particularly important to study the characteristics of planets as a function of the effective gravitational influence of the companion. A compilation of planets in binary systems was made; a search for companions orbiting stars recently shown to host planets was performed, resulting in the addition of two further binary planet hosts (HD 20782 and HD 109749). The probable original properties of the three binary planet hosts with white dwarfs companions were also investigated. Using this updated sample of planets in binaries we performed a statistical analysis of the distributions of planet mass, period, and eccentricity, fraction of multiplanet systems, and stellar metallicity for planets orbiting components of tight and wide binaries and single stars. The only highly significant difference revealed by our analysis concerns the mass distribution of short-period planets. Massive planets in short period orbits are found in most cases around the components of rather tight binaries. The properties of exoplanets orbiting the components of wide binaries are compatible with those of planets orbiting single stars, except for a possible greater abundance of high-eccentricity planets. The previously suggested lack of massive planets with P&gt;100 days in binaries is not confirmed. We conclude that the presence of a stellar companion with separation smaller than 100-300 AU is able to modify the formation and/or migration and/or the dynamical evolution history of giant planets while wide companions play a more limited role

Motivation & Objective

• To investigate how the gravitational influence of a stellar companion in binary systems affects planetary system formation and evolution.
• To determine whether planets in wide binaries differ significantly from those orbiting single stars in mass, period, eccentricity, and multiplicity.
• To assess the role of binary separation in shaping the observed distributions of exoplanet properties, especially for giant planets.
• To update the sample of known planets in binary systems by identifying new binary hosts and re-evaluating systems with white dwarf companions.
• To test the validity of previous claims—such as the lack of massive planets with P > 100 days in binaries—using a larger, more homogeneous dataset.

Proposed method

• Compiled an updated sample of exoplanets in binary systems, including newly identified hosts (HD 20782, HD 109749) through companion searches.
• Performed statistical analysis comparing distributions of planet mass, orbital period, eccentricity, multiplanet fraction, and stellar metallicity across tight binaries, wide binaries, and single stars.
• Used radial velocity and astrometric data to assess the dynamical compatibility of planetary and binary orbits, particularly in systems like HD 189733 and HD 219449.
• Evaluated the original properties (mass ratio, separation) of three systems with white dwarf companions using evolutionary models and orbital constraints.
• Applied criteria from the Catalog of Nearby Exoplanets (B06) and cross-referenced with other databases (e.g., Extrasolar Planet Encyclopedia) to ensure sample consistency.
• Conducted follow-up analysis on candidate companions using adaptive optics, radial velocity, and astrometric data to confirm or rule out physical association.

Experimental results

Research questions

• RQ1 Does the presence of a stellar companion in a binary system alter the distribution of planetary masses, periods, and eccentricities compared to single-star systems?
• RQ2 Are massive planets with orbital periods longer than 100 days absent in binary systems, as previously suggested?
• RQ3 How does binary separation—specifically tight vs. wide systems—affect the formation and dynamical evolution of giant planets?
• RQ4 To what extent do systems with white dwarf companions retain information about their original binary configurations and planetary system properties?
• RQ5 Are there detectable differences in the multiplicity or orbital architecture of planetary systems in wide binaries compared to single stars?

Key findings

• The only highly significant difference found is that massive planets in short-period orbits (P < 100 days) are predominantly found around components of tight binaries (separations < 100–300 AU).
• Planets orbiting components of wide binaries show statistical properties—such as mass, period, and eccentricity distributions—that are largely compatible with those of planets around single stars.
• The previously reported lack of massive planets with P > 100 days in binaries is not confirmed by the updated sample and statistical analysis.
• There is a possible excess of high-eccentricity planets in wide binary systems, suggesting a subtle dynamical influence from distant companions.
• The presence of a companion with separation smaller than 100–300 AU significantly affects the formation, migration, or dynamical evolution of giant planets.
• Three systems with white dwarf companions (HD 20782, HD 109749, GL 86) are likely to have had original binary separations consistent with the observed planetary system properties, indicating that planetary systems can survive post-main-sequence evolution in binary configurations.