SFADI: the Speckle-Free Angular Differential Imaging method

Abstract

We present a new processing technique aimed at significantly improving the angular differential imaging method (ADI) in the context of high-contrast imaging of faint objects nearby bright stars in observations obtained with extreme adaptive optics (EXAO) systems. This technique, named "SFADI" for "Speckle-Free ADI", allows to improve the achievable contrast by means of speckles identification and suppression. This is possible in very high cadence data, which freeze the atmospheric evolution. Here we present simulations in which synthetic planets are injected into a real millisecond frame rate sequence, acquired at the LBT telescope at visible wavelength, and show that this technique can deliver low and uniform background, allowing unambiguous detection of $10^{-5}$ contrast planets, from $100$ to $300$ mas separations, under poor and highly variable seeing conditions ($0.8$ to $1.5$ arcsec FWHM) and in only $20$ min of acquisition. A comparison with a standard ADI approach shows that the contrast limit is improved by a factor of $5$. We extensively discuss the SFADI dependence on the various parameters like speckle identification threshold, frame integration time, and number of frames, as well as its ability to provide high-contrast imaging for extended sources, and also to work with fast acquisitions.

Accepted for publication in ApJ

References in corpus (7)

• The Gemini Planet Imager: First Light
• Solar Magnetic Tracking. I. Software Comparison and Recommended Practices
• Magellan Adaptive Optics first-light observations of the exoplanet $\beta$ Pic b. I. Direct imaging in the far-red optical with MagAO+VisAO and in the near-IR with NICI
• The First Science Results from SPHERE: Disproving the Predicted Brown Dwarf around V471 Tau
• Non-linear propagation of kink waves to the solar chromosphere
• Large Binocular Telescope Interferometer Adaptive Optics: On-sky performance and lessons learned
• Sub-0.1" optical imaging of the Z CMa jets with SPHERE/ZIMPOL