Spin-orbit angle in compact planetary systems perturbed by an inclined companion. Application to the 55 Cancri system

TL;DR

This paper investigates how an inclined stellar companion can influence the spin-orbit alignment in compact planetary systems, with a detailed case study of the 55 Cancri system, revealing possible orbital configurations consistent with observations.

Contribution

It presents a secular evolution model for systems with inclined companions and applies it to 55 Cancri, offering new insights into the origin of its large obliquity.

Findings

Two orbital configurations fit current observations

Inclined binary companions can induce large stellar obliquities

Secular evolution explains observed spin-orbit misalignments

Abstract

The stellar spin orientation relative to the orbital planes of multiplanet systems are becoming accessible to observations. For example, 55 Cancri is a system composed of 5 planets orbiting a member of a stellar binary for which a projected obliquity of 72+-12 deg relative to the orbit of the innermost planet has been reported (Bourrier & Hebrard 2014). This large obliquity has been attributed to the perturbation induced by the binary. Here we describe the secular evolution of similar systems and we discuss the case of the 55 Cancri system more deeply. We provide two different orbital configurations compatible with the currently available observations.