Absence of methane emission from other irradiated disks

Determine why 3.33 μm methane emission has never been observed from disks around other young stars and brown dwarfs if an irradiated disk around LRL 11001 is responsible for its 3.33 μm methane emission.

Background

The paper reports 3.33 μm methane emission from the approximately 6 M_Jup brown dwarf LRL 11001 and considers whether the emission originates in the brown dwarf’s upper atmosphere or in the surface of a circumstellar disk. An irradiated disk is regarded as less likely because the observed hydrocarbon features appear to be produced by the brown dwarf rather than by a disk.

The authors nevertheless identify an unresolved issue: if an irradiated disk around LRL 11001 produces the methane emission, comparable emission should potentially be observable in disks around other young stars and brown dwarfs, yet no such emission has been observed. Resolving this discrepancy would help distinguish between atmospheric and disk-based origins for the emission.