On-sky dark-hole digging with implicit electric field conjugation on MagAO-X

Abstract

Direct spectroscopy is a very promising approach to characterizing the atmospheres of nearby rocky exoplanets, but non-common path aberrations (NCPA), which are differential aberrations between the science optical path and the adaptive optics optical path, can leak through the coronagraph and create speckles that mimic exoplanet signals. This limits the sensitivity of high-contrast imaging instruments at close angular separations - exactly the separations where we want to search for rocky exoplanets with current and future telescopes and instruments. We aim to actively remove the NCPA on-sky during observations by using focal-plane wavefront sensing and control with the newly upgraded MagAO-X instrument. MagAO-X is equipped with a unique second-stage adaptive optics (AO) system containing a dedicated deformable mirror (DM) for coronagraphic focal-plane wavefront control. Because this DM is placed after the science and AO beam splitter, it is not seen by the main AO loop. The DM has been recently upgraded from an ALPAO-97 to a Boston Micromachine Kilo-DM, which enables focal-plane wavefront control with the implicit electric field conjugation (iEFC) algorithm. We developed the necessary procedures to run iEFC with MagAO-X on-sky. We demonstrate the successful removal of NCPA on-sky with an iEFC interaction matrix that was calibrated on the MagAO-X internal source; this demonstrates the repeatability between our off-sky and on-sky alignment. The iEFC algorithm was tested on HR4796A and Alpha Centauri in 0.5” seeing conditions. The intensity of the speckles created by NCPA is reduced by a factor of 2 at the outer working angle and a factor of 20 at the inner working angle. This on-sky validation confirms the robustness and efficiency of iEFC under realistic observing conditions, which paves the way for its integration into next-generation AO systems for the Extremely Large Telescope and Giant Magellan Telescope.