FLIP starlight model for JWST NIRCam raises sensitivity 2–15× and detects 51 Eridani b at 4.3 μm
Authors report a physics-based starlight subtraction method that models telescope instabilities instead of relying on reference images; tested on real JWST coronagraphic data.
A team led by Rodrigo Ferrer-Chavez of Northwestern University has presented a new starlight subtraction method for coronagraphic exoplanet imaging, according to a paper on nature.com 
nature.comnature.comnature.comOpen source ↗. Applied to observations from the Near-InfraRed Camera (NIRCam) coronagraph on the James Webb Space Telescope (JWST), the method reached sensitivity 2–15 times better than standard techniques, the authors report nature.comnature.comnature.comOpen source ↗. It also produced the first detection of the planet 51 Eridani b at 4.3 μm nature.comnature.comnature.comOpen source ↗.
Why reference images fall short
Direct imaging requires suppressing the glare of the host star. Even the brightest young giant planets are about 10^5 times fainter than their stars in the near-infrared nature.comnature.comnature.comOpen source ↗. Standard algorithms model the stellar point spread function (PSF) from reference observations taken at other times or wavelengths, or of other stars nature.comnature.comnature.comOpen source ↗.
These algorithms are limited by telescope instabilities, mostly pointing errors and thermal drifts, which make the reference PSF differ from the science PSF nature.comnature.comnature.comOpen source ↗. Model-based subtraction, which reconstructs the PSF from the physics of the instrument, had been considered a way to relax stability requirements. Earlier studies noted that the complexity of optical systems prevented accurate modelling, and synthetic PSFs on JWST NIRCam had never given sensitivity better than standard techniques, the authors write nature.comnature.comnature.comOpen source ↗.
How FLIP works
The method, called FLIP, first calibrates an instrument model on reference images so that it reproduces the reference PSF. It then solves for small changes in telescope aberrations that better explain the science image nature.comnature.comnature.comOpen source ↗. A multistep optimization combined with a flexible physical model allows instrument instabilities to be modelled and compensated nature.comnature.comnature.comOpen source ↗.
Automatic differentiation is used to optimize millions of model parameters, and GPU-accelerated differentiable models make the computation tractable nature.comnature.comnature.comOpen source ↗. The authors state that, to their knowledge, this is the first time such an approach has shown substantially improved sensitivity on real on-sky coronagraphic images nature.comnature.comnature.comOpen source ↗.
They add that the framework can be extended to other current and future ground-based and space-based observatories, including the Nancy Grace Roman Space Telescope and the Habitable Worlds Observatory (HWO) nature.comnature.comnature.comOpen source ↗. HWO aims to image Earth analogues around Sun-like stars, a 10^10 brightness contrast, which calls for picometre-level stability, 100 to 1,000 times better than JWST nature.comnature.comnature.comOpen source ↗. According to the authors, the approach could potentially relax such stability requirements nature.comnature.comnature.comOpen source ↗.
