Stellar Companions to TESS Objects of Interest: A Test of Planet–Companion Alignment

Abstract

We present a catalog of stellar companions to host stars of Transiting Exoplanet Survey Satellite Objects of Interest (TOIs) identified from a marginalized likelihood ratio test that incorporates astrometric data from the Gaia Early Data Release 3 catalog (EDR3). The likelihood ratio is computed using a probabilistic model that incorporates parallax and proper-motion covariances and marginalizes the distances and 3D velocities of stars in order to identify comoving stellar pairs. We find 172 comoving companions to 170 non-false-positive TOI hosts, consisting of 168 systems with two stars and 2 systems with three stars. Among the 170 TOI hosts, 54 harbor confirmed planets that span a wide range of system architectures. We conduct an investigation of the mutual inclinations between the stellar companion and planetary orbits using Gaia EDR3, which is possible because transiting exoplanets must orbit within the line of sight; thus, stellar companion kinematics can constrain mutual inclinations. While the statistical significance of the current sample is weak, we find that 73⁺¹⁴₋₂₀% of systems with Kepler-like architectures (R_P ≤ 4 R_⊕ and a < 1 AU) appear to favor a nonisotropic orientation between the planetary and companion orbits with a typical mutual inclination α of 35 ± 24∘. In contrast, 65⁺²⁰₋₃₅% of systems with close-in giants (P < 10 days and R_P > 4 R_⊕) favor a perpendicular geometry (α= 89 ± 21∘) between the planet and companion. Moreover, the close-in giants with large stellar obliquities (planet-host misalignment) are also those that favor significant planet-companion misalignment.