Direct Imaging of Exoplanets Beyond the Radial Velocity Limit: Application to the HD 134987 System

TL;DR

This paper demonstrates how future direct imaging can discover exoplanets undetectable by radial velocity methods, using the HD 134987 system as a case study, and explores detection capabilities of upcoming missions.

Contribution

It introduces a method combining RV and direct imaging limits to identify planets detectable only through reflected light, validated with dynamical simulations and applied to future mission concepts.

Findings

Planets can be detected via direct imaging while remaining hidden from RV surveys.

The method is adaptable to other systems and imaging instruments.

Future missions like the Roman Space Telescope and Habitable Exoplanet Observatory can discover new exoplanets.

Abstract

Future direct imaging missions will primarily observe planets that have been previously detected, mostly via the radial velocity (RV) technique, to characterize planetary atmospheres. In the meantime, direct imaging may discover new planets within existing planetary systems that have bright enough reflected flux, yet with insufficient signals for other methods to detect. Here, we investigate the parameter space within which planets are unlikely to be detected by RV in the near future due to precision limitations, but could be discovered through reflected light with future direct imaging missions. We use the HD 134987 system as a working example, combine RV and direct imaging detection limit curves in the same parameter space through various assumptions, and insert a fictitious planet into the system while ensuring it lies between the RV and imaging detection limits. Planet validity tested through dynamical simulations and retrieval tests revealed that the planet could indeed be detected by imaging while remaining hidden from RV surveys. Direct imaging retrieval was carried out using starshade simulations for two mission concepts: the Starshade Rendezvous Probe that could be coupled with the Nancy Grace Roman Space Telescope, and the Habitable Exoplanet Observatory. This method is applicable to any other systems and high contrast direct imaging instruments, and could help inform future imaging observations and data analysis on the discovery of new exoplanets.