Determine the physical origin of the 1.3 μm J-band absorption feature in VHS J1831−5513

Determine the physical origin of the prominent approximately 1.3 μm absorption feature at the J-band peak observed in the Magellan/FIRE near-infrared spectrum of the L/T transition brown dwarf VHS J183135.58−551355.9 (VHS J1831−5513), assessing whether it arises from methane (CH4), telluric contamination, or another absorber.

Background

In the Analysis section, the authors report an unusual absorption feature near 1.3 μm at the J-band peak in the spectrum of VHS J1831−5513. This feature is not reproduced by Sonora models and does not match typical CH4 behavior, although other CH4 features are present elsewhere in the spectrum.

They checked for telluric correction issues and instrumental artifacts but found no obvious cause, and note a nearby telluric O2 band that could contribute. The feature is therefore characterized as an unknown absorber, motivating higher resolution and higher signal-to-noise spectroscopy and retrieval analyses to determine its origin.