Investigating the High-energy Radiation Environment of Planets in Sun-like Binary Systems

TL;DR

This work tackles how X-ray–UV irradiation from Sun-like binary stars shapes exoplanetary photochemistry and atmospheric escape, with emphasis on FUV drivers and the uncertain EUV regime. Using the SISTINE rocket, the authors obtain a simultaneous 980–1570 Å spectrum of α Cen AB and build comprehensive SEDs spanning $5$ Å to $1$ mm by merging archival data, model spectra, and a stellar activity model. They then simulate atmospheric abundances for a hypothetical planet around α Cen A under minimum and maximum irradiation using the VULCAN chemical kinetics code. The results indicate that binarity-induced enhancement of atmospheric mass loss is unlikely to pose a major obstacle for future exoplanet surveys like Habitable Worlds Observatory, supporting the viability of Earth-like planet searches around Sun-like binaries.

Abstract

Far-ultraviolet (FUV) radiation is a driving source of photochemistry in planetary atmospheres. Proper interpretation of atmospheric observations requires a full understanding of the radiation environment that a planet is exposed to. Using the Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SISTINE) rocket-borne spectrograph, we observed the Sun-like binary system $α$ Centauri AB and captured the FUV spectrum of both stars simultaneously. Our spectra cover 980--1570 Å, providing the broadest FUV wavelength coverage taken in a single exposure and spanning several key stellar emission features which are important photochemical drivers. Combining the SISTINE spectrum with archival observations, model spectra, and a novel stellar activity model, we have created spectral energy distributions (SEDs) spanning 5 Å--1 mm for both $α$ Centauri A and B. We use the SEDs to estimate the total high-energy flux (X-ray--UV) incident on a hypothetical exoplanet orbiting $α$ Centauri A. Because the incident flux varies over time due to the orbit of the stellar companion and the activity level of each star, we use the VULCAN photochemical kinetics code to estimate atmospheric chemical abundances in the case of minimum and maximum flux exposure. Our results indicate that enhanced atmospheric mass loss due to stellar binarity will likely not be an issue for future exoplanet-hunting missions such as the Habitable Worlds Observatory when searching for Earth-like planets around Sun-like stars.