2017MNRAS.464.1108Z

The origin of the very red optical and infrared colours of intermediate-age (∼10-500 Myr) L-type dwarfs remains unknown. It has been suggested that low-gravity atmospheres containing large amounts of dust may account for the observed reddish nature. We explored an alternative scenario by simulating debris disc around G 196-3 B, which is an L3 young brown dwarf with a mass of ∼15 M_Jup and an age in the interval 20-300 Myr. The best-fit solution to G 196-3 B's photometric spectral energy distribution from optical wavelengths through 24 µm corresponds to the combination of an unreddened L3 atmosphere (T_eff ≃ 1870 K) and a warm (≃1280 K), narrow (≃0.07-0.11 R_☉) debris disc located at very close distances (≃0.12-0.20 R_☉) from the central brown dwarf. This putative, optically thick, dusty belt, whose presence is compatible with the relatively young system age, would have a mass >=7 x 10^–10 M_⊕ comprised of submicron/micron characteristic dusty particles with temperatures close to the sublimation threshold of silicates. Considering the derived global properties of the belt and the disc-to-brown dwarf mass ratio, the dusty ring around G 196-3 B may resemble the rings of Neptune and Jupiter, except for its high temperature and thick vertical height (≃6 x 10³ km). Our inferred debris disc model is able to reproduce G 196-3 B's spectral energy distribution to a satisfactory level of achievement.