Direct Exoplanet Detection with Binary Differential Imaging

TL;DR

Binary Differential Imaging (BDI) leverages simultaneous imaging of binary stars to improve exoplanet detection sensitivity, outperforming traditional methods like ADI, especially for planets close to their host stars, and is promising for future space telescopes.

Contribution

This paper introduces BDI as a novel technique for direct exoplanet imaging that enhances sensitivity and efficiency by imaging binary stars simultaneously, a significant improvement over existing methods.

Findings

BDI achieves ~0.5 mag better contrast than ADI within 1 arcsecond.

BDI is 2-4 times more efficient than ADI and classical PSF subtraction.

Preliminary observations demonstrate BDI's potential in detecting exoplanets in binary systems.

Abstract

Binaries are typically excluded from direct imaging exoplanet surveys. However, the recent findings of Kepler and radial velocity programs show that planets can and do form in binary systems. Here, we suggest that visual binaries offer unique advantages for direct imaging. We show that Binary Differential Imaging (BDI), whereby two stars are imaged simultaneously at the same wavelength within the isoplanatic patch at high Strehl ratio, offers improved point spread function (PSF) subtraction that can result in increased sensitivity to planets close to each star. We demonstrate this by observing a young visual binary separated by 4\asec ~with MagAO/Clio-2 at 3.9 \microns, where the Strehl ratio is high, the isoplanatic patch is large, and giant planets are bright. Comparing BDI to angular differential imaging (ADI), we find that BDI's 5$\sigma$ contrast is \about 0.5 mags better than ADI's within \about 1\asec ~for the particular binary we observed. Because planets typically reside close to their host stars, BDI is a promising technique for discovering exoplanets in stellar systems that are often ignored. BDI is also 2-4$\times$ more efficient than ADI and classical reference PSF subtraction, since planets can be detected around both the target and PSF reference simultaneously. We are currently exploiting this technique in a new MagAO survey for giant planets in 140 young nearby visual binaries. BDI on a space-based telescope would not be limited by isoplanatism effects and would therefore be an even more powerful tool for imaging and discovering planets.