No Giant Planets in the Eta Cassiopeiae System: Dynamical Implications of a Wide Binary Companion

Given the vast number of stars that exist within binary systems, it remains important to explore the effect of binary star environments on the formation and evolution of exoplanetary systems. Nearby binaries provide opportunities to characterize their properties and orbits through a combination of radial velocities, astrometry, and direct imaging. Eta Cassiopeiae is a bright, well-known binary system for which recent observations have provided greatly improved stellar masses and orbital parameters. We present additional radial velocity data that are used to perform an injection-recovery analysis for potential planetary signatures. We further provide a detailed dynamical study that explores the viability of planetary orbits throughout the system. Our combined analysis shows that giant planets are significantly ruled out for the system, and indeed no planetary orbits are viable beyond ∼8 au of the primary star. However, terrestrial planets may yet exist within the habitable zone where orbits can remain long-term stable. We discuss the implications of these results, highlighting the effect of wide binary companions on giant planet formation, and the consequences for occurrence rates and planetary habitability.