X-Shooter spectra of young LT dwarfs

These young planetary-mass brown dwarfs have spectral types L and T; they are shaped by molecular absorption and modified by their low gravity, which makes them distinct from field objects. We aim to provide a detailed characterization of near-infrared spectra for young LT brown dwarfs, including robust spectral typing, calibrating spectral indices, identifying possible binaries, and selecting suitable spectral standards.

We processed and analyzed archival spectra from VLT/X-shooter for a sample of 56 dwarfs with ages between 10 and 600Myr and spectral types between late-M and mid-T. We re-determine spectral types by comparing them with a set of literature templates and assess a large range of spectral indices, calibrated using a specifically designed literature sample. We are able to identify 15 spectral indices that are useful for spectral typing for specific spectral ranges discussed here and provide the scaling relations with spectral types.