K-Stacker, a new way of detecting and characterizing exoplanets with high contrast imaging instruments

Abstract

This year, a second generation of coronagraphs dedicated to high-contrast direct imaging of exoplanets is starting operations. Among them, SPHERE, installed at the focus of the UT3 Very Large Telescope, reaches unprecedented contrast ratios up to 10 −6 -10 −7 , using eXtreme Adaptive Optics and the Angular Differential Imaging (ADI) techniques. In this paper, we present a new method called Keplerian-Stacker that improves the detection limit of high contrast instruments like SPHERE, by up to a factor of 10. It consists of observing a star on a long enough period to let a hypothetical planet around that star move along its orbit. Even if in each individual observation taken during one night, we do not detect anything, we show that it is possible, using an optimization algorithm, to re-center the images according to keplerian motions (ex: 10-100 images taken over a long period of typically 1-10 years) and detect planets otherwise unreachable. This method can be used in combination with the ADI technics (or possibly any other high contrast data reduction method) to improve the Signal to Noise Ratio in each individual image, and to further improve the global detection limit. It also directly provides orbital parameters of the detected planets, as a by-product of the optimization algorithm.

Deep orbital search for additional planets in the HR 8799 system

“…This approach is similar to Mawet et al (2019) in which direct images of Eridani are combined with radial velocity data; however, we do not include radial velocities (the planets of HR 8799 orbit almost face on from our perspective) but instead combine images from multiple epochs as in Skemer & Close (2011). It also shares some similarities in concept with those of K-stacker (Coroller et al 2015;Nowak et al 2018) and for example the recent results of Le Coroller et al (2022).…”