T dwarf

[6] This object had a temperature below 1000 K and showed methane (CH4), water vapor (H2O) and carbon monoxide (CO) in its spectrum.

[12] Later work found a dynamical mass of 70 ± 5 MJ for Gliese 229B, which is much higher than the cooling models would suggest.

[13] It is also suspected that Gliese 229B is a binary, which could explain its high mass and its unusual spectrum.

It shows a hint of FeH in the spectrum, which weakens in late L dwarfs, but strengthens in early to mid T-dwarfs due to cloud disruption.

[24][25] Observations of T-dwarfs in the near- and mid-infrared with JWST clearly show additional absorption features due to NH3, CH4, H2O, CO and carbon dioxide (CO2).

It shows blue near-infrared colors due to suppression of the 2.1 μm peak, likely caused by enhanced collision induced absorption (CIA) of hydrogen (H2).

This work also identified three brown dwarfs that are candidate members of stellar streams.

Future works with JWST, Euclid, Rubin and Roman will increase the sample of T subdwarfs to thousands.

[42] Another significant discovery is one of the closest planetary-mass objects, called SIMP J013656.5+093347 (T2.5, 12.7 ±1.0 MJ), which is part of the 200 Myr old Carina-Near moving group.

[45] Young directly imaged exoplanets and planetary-mass companions sometimes show a T spectral type, such as 51 Eridani b (T4.5-T6).

[4] Two of the most variable brown dwarfs are the T-dwarfs Luhman 16B, showing a variation up to 20%[46] and 2MASS J2139+02, which varies with an amplitude as high as 26%.

The variability has been connected to the presence of clouds, but other explanations were proposed, such as hot spots and aurorae.

This explains the reappearance and strengthening of FeH and the blue near-infrared color for early to mid T-dwarfs.

[25] Late T-dwarfs should also have cloud layers made of chromium, potassium chloride and different sulfides.

[53] Radio emission in T-dwarfs is thought to be generated by an aurora, similar to late L-dwarfs.