JWST-TST High Contrast: JWST/NIRCam observations of the young giant planet $\beta$ Pic b

Abstract

We present the first JWST/NIRCam observations of the directly-imaged gas giant exoplanet $\beta$ Pic b. Observations in six filters using NIRCam's round coronagraphic masks provide a high signal-to-noise detection of $\beta$ Pic b and the archetypal debris disk around $\beta$ Pic over a wavelength range of $\sim$1.7-5 $\mu$m. This paper focuses on the detection of $\beta$ Pic b and other potential point sources in the NIRCam data, following a paper by Rebollido et al. which presented the NIRCam and MIRI view of the debris disk around $\beta$ Pic. We develop and validate approaches for obtaining accurate photometry of planets in the presence of bright, complex circumstellar backgrounds. By simultaneously fitting the planet's PSF and a geometric model for the disk, we obtain planet photometry that is in good agreement with previous measurements from the ground. The NIRCam data supports the cloudy nature of $\beta$ Pic b's atmosphere and the discrepancy between its mass as inferred from evolutionary models and the dynamical mass reported in the literature. We further identify five additional localized sources in the data, but all of them are found to be background stars or galaxies based on their color or spatial extent. We can rule out additional planets in the disk midplane above 1 Jupiter mass outward of 2 arcsec ($\sim$40 au) and away from the disk midplane above 0.05 Jupiter masses outward of 4 arcsec ($\sim$80 au). The inner giant planet $\beta$ Pic c remains undetected behind the coronagraphic masks of NIRCam in our observations.