Direct Exoplanet Detection with Binary Differential Imaging

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.

Accepted to ApJ on Aug. 30, 2015. 9 pages (emulateapj), 4 figures. Full-resolution version available upon request

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Cited by in corpus (9)

• Imaging Extrasolar Giant Planets
• Characterization of exoplanets from their formation III: The statistics of planetary luminosities
• On-sky performance analysis of the vector Apodizing Phase Plate coronagraph on MagAO/Clio2
• Reference-star differential imaging on SPHERE/IRDIS
• SPOTS: The Search for Planets Orbiting Two Stars. III. Complete Sample and Statistical Analysis
• Techniques for High-Contrast Imaging in Multi-Star Systems II: Multi-Star Wavefront Control
• MagAO: Status and Science
• Companion Mass Limits for 17 Binary Systems Obtained with Binary Differential Imaging and MagAO/Clio
• HIP 67506 C: MagAO-X Confirmation of a New Low-Mass Stellar Companion to HIP 67506 A