Data post-processing gain resulting from the patchy nature of speckles

TL;DR

This paper demonstrates that the patchy nature of speckles can significantly improve the sensitivity of exoplanet imaging, especially when combining observations at different angles, surpassing traditional noise assumptions.

Contribution

It reveals that exploiting speckle patchiness in ADI observations can enhance signal-to-noise ratios beyond standard expectations, offering a new approach for exo-Earth detection strategies.

Findings

Combining two observatory roll angles yields >√2 SNR gain.

The gain approaches a factor of 2 when speckle noise dominates.

Patchy speckles can be leveraged to improve detection sensitivity.

Abstract

The data post-processing gain is an important parameter for exposure time calculations used to inform the design of the Habitable Worlds Observatory (HWO). Assuming azimuthally symmetric noise properties is a common simplifying assumption for such simulations, which neglects the patchy nature of the residual diffracted starlight; i.e., speckles. Fortunately, patchiness might prove to be an opportunity that improves the overall sensitivity of observatory assuming photon-noise limited speckle subtraction. We illustrate this effect in the context of angular differential imaging (ADI), which is one of the possible observing strategies being considered for the detection and characterization of exo-Earth with HWO. We show that combining observations of two observatory roll angles leads to a gain in signal-to-noise greater than $\sqrt{2}$ when the patchy starlight dominates other noise sources. The gain can be closer to x2 when the starlight dominates the noise budget by more than an order of magnitude. In other words, combining good and bad observations is better than combining two average ones. This statement is very general as it is a direct consequence of combining data with a weighted mean. It applies more broadly to any combination of observations with varying noise level.