A Detailed Investigation of the Proposed NN Serpentis Planetary System

TL;DR

This paper investigates the orbital stability of proposed planetary systems around NN Serpentis, finding that only resonant configurations are stable and emphasizing the need for further observations to clarify the system's true architecture.

Contribution

It provides a dynamical analysis of proposed NN Serpentis planetary system architectures and offers a revised orbital solution without artificial eccentricity constraints.

Findings

Resonant orbital configurations are necessary for stability.

Allowing eccentricity leads to system instability.

Further observations are needed to confirm the system's architecture.

Abstract

The post-main sequence eclipsing binary NN Serpentis was recently announced as the potential host of at least two massive planetary companions. In that work, the authors put forward two potential architectures that fit the observations of the eclipsing binary with almost identical precision. In this work, we present the results of a dynamical investigation of the orbital stability of both proposed system architectures, finding that they are only stable for scenarios in which the planets are locked in mutual mean motion resonance. In the discovery work, the authors artificially fixed the orbital eccentricity of the more massive planet, NN Ser(AB) c, at 0. Here, we reanalyse the observational data on NN Serpentis without this artificial constraint, and derive a new orbital solution for the two proposed planets. We detail the results of further dynamical simulations investigating the stability of our new orbital solution, and find that allowing a small non-zero eccentricity for the outer planet renders the system unstable. We conclude that, although the original orbits proposed for the NN Serpentis planetary system prove dynamically feasible, further observations of the system are vital in order to better constrain the system's true architecture.