SFADI: the Speckle-Free Angular Differential Imaging method

TL;DR

SFADI is a novel high-contrast imaging technique that enhances the detection of faint objects near bright stars by suppressing speckles in high-cadence adaptive optics data, significantly improving contrast limits.

Contribution

The paper introduces SFADI, a speckle suppression method for ADI that achieves better contrast in high-cadence observations, enabling detection of very faint exoplanets under challenging conditions.

Findings

Achieves contrast of 10^-5 at 100-300 mas separations

Improves contrast limit by a factor of 5 over standard ADI

Effective in poor and variable seeing conditions

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.