N-body models exclude disc-ejection origin for hydrocarbon-rich H-type objects in IC 348
Spatial and kinematic evidence indicates H-type objects formed via turbulent fragmentation or disc fragmentation at large radii rather than ejection from inner discs. This tightens the mass threshold separating star-like and planet-like formation channels ahead of JWST and Roman surveys of additional clusters. Future proper-motion measurements at 0.1 mas yr^-1 precision can falsify the remaining wide-orbit ejection channel within three years.
The study combines Gaia astrometry, JWST NIRSpec spectra, and 10^4 N-body realizations of the IC 348 cluster. Planets placed at 5 au around solar-mass stars and ejected by stellar fly-bys reproduce the observed number of free-floaters but produce a velocity dispersion 2.8 times larger and a half-mass radius 1.7 times greater than the H-type population, which remains indistinguishable from the stellar distribution at Kolmogorov-Smirnov p=0.72.
Parker: Proper-motion surveys of IC 348 with 0.1 mas yr^-1 precision will detect <5% of H-type objects with velocities >3 km s^-1 within 36 months if star-like formation dominates.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2606.09979)
- [2]Supporting Source(https://arxiv.org/abs/2401.01933)