Bayesian Characterisation of Circumbinary Exoplanets with LISA

TL;DR

This paper introduces a Bayesian method for detecting and characterizing circumbinary exoplanets and brown dwarfs with LISA, revealing how these third bodies influence binary signals and their detectability.

Contribution

First fully Bayesian analysis of sub-stellar objects with LISA, including orbital eccentricity, and assessment of their detectability and impact on binary parameter estimation.

Findings

Posterior behavior bifurcates based on third-body period relative to observation time.

Undetectable third bodies can bias inner binary parameters.

Predicted number of detectable brown dwarf systems in the catalogue.

Abstract

The Laser Interferometer Space Antenna (LISA) will detect and characterize $\sim10^4$ Galactic Binaries consisting predominantly of two White Dwarfs (WD). An interesting prospect within this population is a third object--another WD star, a Circumbinary Exoplanet (CBP), or a Brown Dwarf (BD)--in orbit about the inner WD pair. We present the first fully Bayesian detection and posterior analysis of sub-stellar objects with LISA, focusing on the characterization of CBPs. We used an optimistic astrophysically motivated catalogue of these CBP third-body sources, including their orbital eccentricity around the inner binary for the first time. We examined Bayesian Evidence computations for detectability, as well as the effects on the posterior distributions for both the inner binary parameters and the third-body parameters. We find that the posterior behavior bifurcates based on whether the third-body period is above or below half the observation time. Additionally, we find that undetectable third-body sources can bias the inner binary parameters whether or not the correct template is used. We used the information retrieved from the study of the CBP population to make an initial conservative prediction for the number of detectable BD systems in the original catalogue. We end with commentary on the predicted qualitative effects on LISA global fitting and Galactic Binary population analysis. The procedure used in this work is generic and can be directly applied to other astrophysical effects expected within the Galactic Binary population.