Probing Photon Statistics in Adaptive Optics Images with SCExAO/MEC

TL;DR

This paper explores photon statistics in high-contrast imaging using MKID detectors behind SCExAO, demonstrating how photon arrival time data can distinguish exoplanets from speckles and discussing future improvements for on-sky applications.

Contribution

It introduces the application of photon arrival time statistics and the SSD technique to high-contrast imaging, including the first demonstration on an extended source and simulation-based analysis of PCSSD limitations.

Findings

Photon statistics match expected distributions for on-axis and off-axis sources.

SSD can distinguish companions from speckles using photon arrival times.

Simulations reveal current limitations and future pathways for PCSSD on-sky use.

Abstract

We present an experimental study of photon statistics for high-contrast imaging with the Microwave Kinetic Inductance Detector (MKID) Exoplanet Camera (MEC) located behind the Subaru Coronagraphic Extreme Adaptive Optics System (SCExAO) at the Subaru Telescope. We show that MEC measures the expected distributions for both on-axis companion intensity and off-axis intensity which manifests as quasi-static speckles in the image plane and currently limits high-contrast imaging performance. These statistics can be probed by any MEC observation due to the photon-counting capabilities of MKID detectors. Photon arrival time statistics can also be used to directly distinguish companions from speckles using a post-processing technique called Stochastic Speckle Discrimination (SSD). Here, we we give an overview of the SSD technique and highlight the first demonstration of SSD on an extended source -- the protoplanetary disk AB Aurigae. We then present simulations that provide an in-depth exploration as to the current limitations of an extension of the SSD technique called Photon-Counting SSD (PCSSD) to provide a path forward for transitioning PCSSD from simulations to on-sky results. We end with a discussion of how to further improve the efficacy of such arrival time based post-processing techniques applicable to both MKIDs, as well as other high speed astronomical cameras.