Millisecond exoplanet imaging: II. regression equations and technical discussion

Abstract

The leading difficulty in achieving the contrast necessary to directly image exoplanets and associated structures (e.g., protoplanetary disks) at wavelengths ranging from the visible to the infrared are quasistatic speckles, and they are hard to distinguish from planets at the necessary level of precision. The source of the quasi-static speckles is hardware aberrations that are not compensated by the adaptive optics (AO) system. These aberrations are called non-common path aberrations (NCPA) by the community. In 2013, Frazin showed how, in principle, simultaneous millisecond (ms) telemetry from the wavefront sensor (WFS) and the science camera behind a stellar coronagraph can be used as input into a regression scheme that simultaneously and self-consistently estimates the NCPA and the sought-after image of the planetary system (the exoplanet image). The physical principle underlying the regression method is rather simple: the wavefronts, which are measured by the WFS, modulate the speckles caused by the NCPA and therefore can be used as probes of the optical system. The simulations in the Part I article provide results on the joint regression on the NCPA and the exoplanet image from three different methods, called the ideal, the naïve, and the bias-corrected estimators. The ideal estimator is not physically realizable but is a useful as a benchmark for simulation studies, but the other two are, at least in principle. This article provides the regression equations for all three of these estimators as well as a supporting technical discussion. Briefly, the naïve estimator simply uses the noisy WFS measurements without any attempt to account for the errors, and the bias-corrected estimator uses statistical knowledge of the wavefronts to treat errors in the WFS measurements.

Speckle Space–Time Covariance in High-contrast Imaging

“…(Note: recent work from Mullen et al (2019) shows that using KLIP on shorter exposures may even help remove quasi-static speckles more effectively, further bolstering the case for the stKLIP's effectiveness in this regime.) Additionally, the presence of atmospheric residuals could even provide information about the phase of quasi-static speckles, allowing them to be effectively nulled with a deformable mirror (Frazin 2014;Frazin & Rodack 2021). Future simulations may explore this regime and determine if additional contrast gain is possible.…”