ESCAPE project: fundamental detection limits of JWST/NIRCam coronographic observations

TL;DR

This paper investigates the fundamental detection limits of JWST/NIRCam coronagraphy, showing that current post-processing techniques are far from these limits, especially at shorter separations, and proposes analytical methods for quick estimates.

Contribution

It introduces an analytical approach to estimate the fundamental contrast limit of JWST/NIRCam coronagraphy, providing a faster alternative to computationally intensive MCMC methods.

Findings

Fundamental contrast is significantly deeper than current post-processed limits.

At 0.5'' and 1'', contrast limits are 10 and 4 times deeper respectively.

Shorter separations could benefit from improved post-processing techniques.

Abstract

In this study, we explored the fundamental contrast limit of NIRCam coronagraphy observations, representing the achievable performance with post-processing techniques. This limit is influenced by photon noise and readout noise, with complex noise propagation through post-processing methods like principal component analysis. We employed two approaches: developing a formula based on simplified scenarios and using Markov Chain Monte Carlo (MCMC) methods, assuming Gaussian noise properties and uncorrelated pixel noise. Tested on datasets HIP\,65426, AF\,Lep, and HD\,114174, the MCMC method provided accurate but computationally intensive estimates. The analytical approach offered quick, reliable estimates closely matching MCMC results in simpler scenarios. Our findings showed the fundamental contrast curve is significantly deeper than the current achievable contrast limit obtained with post-processing techniques at shorter separations, being 10 times deeper at $0.5''$ and 4 times deeper at $1''$. At greater separations, increased exposure time improves sensitivity, with the transition between photon and readout noise dominance occurring between $2''$ and $3''$. We conclude the analytical approach is a reliable estimate of the fundamental contrast limit, offering a faster alternative to MCMC. These results emphasize the potential for greater sensitivity at shorter separations, highlighting the need for improved or new post-processing techniques to enhance JWST NIRCam sensitivity or contrast curve.