Detecting Exoplanets Using Eclipsing Binaries as Natural Starshades

TL;DR

This paper proposes using eclipsing binaries as natural starshades to enhance direct imaging of exoplanets, potentially enabling detection of fainter and smaller planets around binary systems with current and future telescopes.

Contribution

It introduces a novel observational technique leveraging eclipses in binary stars to improve exoplanet detection contrast, expanding capabilities for imaging smaller and fainter planets.

Findings

Eclipsing binaries can boost planet-star contrast by over 10 times during eclipse.

Current instruments can detect super-Jupiter planets around young binaries using this method.

Future telescopes could image Earth-like planets in favorable binary systems.

Abstract

We investigate directly imaging exoplanets around eclipsing binaries, using the eclipse as a natural tool for dimming the binary and thus increasing the planet to star brightness contrast. At eclipse, the binary becomes point-like, making coronagraphy possible. We select binaries where the planet-star contrast would be boosted by $>10\times$ during eclipse, making it possible to detect a planet that is $\gtrsim10\times$ fainter or in a star system that is $\sim2$-$3\times$ more massive than otherwise. Our approach will yield insights into planet occurrence rates around binaries versus individual stars. We consider both self-luminous (SL) and reflected light (RL) planets. In the SL case, we select binaries whose age is young enough so that an orbiting SL planet would remain luminous; in U Cep and AC Sct, respectively, our method is sensitive to SL planets of $\sim$4.5$M_J$ and $\sim$9$M_J$ with current ground- or near-future space-based instruments, and $\sim$1.5$M_J$ and $\sim$6$M_J$ with future ground-based observatories. In the RL case, there are three nearby ($\lesssim50$ pc) systems -- V1412 Aql, RR Cae, RT Pic -- around which a Jupiter-like planet at a planet-star separation of $\gtrsim20$ mas might be imaged with future ground- and space-based coronagraphs. A Venus-like planet at the same distance might be detectable around RR Cae and RT Pic. A habitable Earth-like planet represents a challenge; while the planet-star contrast at eclipse and planet flux are accessible with a 6-8m space telescope, the planet-star separation is 1/3 - 1/4 of the angular separation limit of modern coronagraphy.