JWST/NIRCam Imaging of Young Stellar Objects. II. Deep Constraints on Giant Planets and a Planet Candidate Outside of the Spiral Disk Around SAO 206462

Abstract

We present JWST/NIRCam F187N, F200W, F405N, and F410M direct imaging data of the disk surrounding SAO 206462. Previous images show a very structured disk, with a pair of spiral arms thought to be launched by one or more external perturbers. The spiral features are visible in three of the four filters, with the nondetection in F410M due to the large detector saturation radius. We detect with a signal-to-noise ratio of 4.4 a companion candidate that, if on a coplanar circular orbit, would orbit SAO 206462 at a separation of ∼300 au, 2.25 σ away from the predicted separation for the driver of the eastern spiral. No other companion candidates were detected. At the location predicted by simulations of both spirals generated by a single massive companion, the NIRCam data exclude objects more massive than ∼2.2 M _J assuming the BEX evolutionary models. In terms of temperatures, the data are sensitive to objects with T _eff ∼ 650–850 K, when assuming planets emit like blackbodies ( R _p between 1 and 3 R _J ). From these results, we conclude that if the spirals are driven by gas giants, these must be either cold or embedded in circumplanetary material. In addition, the NIRCam data provide tight constraints on ongoing accretion processes. In the low extinction scenario we are sensitive to mass accretion rates of the order $\dot{M}\sim {10}^{-9}{M}_{{\rm{J}}}$ yr ^−1 . Thanks to the longer wavelengths used to search for emission lines, we reach unprecedented sensitivities to processes with $\dot{M}\sim {10}^{-7}{M}_{{\rm{J}}}$ yr ^−1 even toward highly extincted environments ( A _V ≈ 50 mag).

Keywords

• Exoplanet formation
• Protoplanetary disks
• Direct imaging