Author ORCID Identifier

Kimberly Ward-Duong: 0000-0002-4479-8291

Mickaël Bonnefoy: 0000-0001-5579-5339

Nicole Arulanantham: 0000-0003-2631-5265

Benoît Tabone: 0000-0002-1103-3225

Catherine Dougados: 0000-0001-6660-936X

Laurent Pueyo: 0000-0003-3818-408X

Mathilde Mâlin: 0000-0002-2918-8479

Document Type

Article

Publication Date

6-2026

Publication Title

The 23rd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun

Abstract

We present near- to mid-infrared spectroscopy of the young (2 Myr), wide-orbit planetary mass companion SR 12 c, recently observed with JWST at unprecedented spectral resolution and sensitivity. With a mass of only 11 Jupiter masses, and a projected separation of nearly 1000 au from its cool (K+M type) binary host, SR 12 c represents an important and uniquely accessible case study of a circumplanetary disk. It is one of only three such objects detected to date in ALMA continuum observations, alongside the PDS 70 system and the free-floating planet OTS 44. Using JWST/MRS spectra at R3000, we characterize the circumplanetary disk dust temperature and composition of SR 12 c, finding strong evidence for at least six complex gas-phase hydrocarbon species. As SR 12 c is the planetary-mass object with the broadest observed wavelength coverage to date, spanning the ultraviolet through the submillimeter, we place its NIR-MIR spectra and derived atmospheric and disk properties in context with previous accretion studies, providing a direct comparison of disk gas and dust. The combination of high spectral resolution and broad wavelength coverage also makes SR 12 c an excellent test case for detailed thermochemical modeling of its disk, an approach previously applied only to stellar systems. This young circumplanetary disk represents a critical addition to the small but growing population of disks identified around the coolest substellar objects, indicating that the complex, carbon-rich chemistry observed around the lowest-mass stars and brown dwarfs can extend in a self-similar manner to the small disks surrounding young giant planets.

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