Fast Coherent Differential Imaging on Ground-based Telescopes Using the Self-coherent Camera

摘要

Direct imaging and spectral characterization of exoplanets using extreme adaptive optics (ExAO) is a key sciencegoal of future extremely large telescopes and space observatories. However, quasi-static wavefront errors will limitthe sensitivity of this endeavor. Additional limitations for ground-based telescopes arise from residual AO-corrected atmospheric wavefront errors, generating millisecond-lifetime speckles that average into a halo over along exposure. A solution to both of these problems is to use the science camera of an ExAO system as a wavefrontsensor to perform a fast measurement and correction method to minimize these aberrations as soon as they aredetected. We develop the framework for one such method based on the self-coherent camera (SCC) to be applied toground-based telescopes, called the Fast Atmospheric SCC Technique (FAST). We show that with the use of aspecially designed coronagraph and coherent differential imaging algorithm, recording images every fewmilliseconds allows for a subtraction of atmospheric and static speckles while maintaining an algorithmicexoplanet throughput close to unity. Detailed simulations reach a contrast close to the photon noise limit after 30 sfor a 1% bandpass in the H band on both zeroth and fifth magnitude stars. For the latter case, this is about 110 timesbetter in raw contrast than what is currently achieved from ExAO instruments if we extrapolate for an hour ofobserving time, illustrating that the improvement in sensitivity from this method could play an important role in thefuture detection and characterization of lower mass exoplanets.