We have obtained a good quality R \sim 400 0.8–2.5 \mu m spectrum and accurate photometry of Gl 570D , one of the coolest and least luminous brown dwarfs currently known .
The spectrum shows that Gl 570D has deeper absorptions in the strong water and methane bands at 1.12–1.17 \mu m , 1.33–1.45 \mu m , 1.62–1.88 \mu m , and 2.20–2.45 \mu m and is both bluer at J - K and redder at K - L ^ { \prime } than previously observed T dwarfs .
Data analysis using model spectra coupled with knowledge of the well-understood primary implies that for the same surface gravity , Gl 570D is about 160 K cooler than Gl 229B .
For an age range of 2–5 Gyr Gl 570D has an effective temperature in the range 784–824 K , a log gravity in the range 5.00–5.27 cm s ^ { -2 } , and a luminosity in the range 2.88-2.98 \times 10 ^ { -6 } L _ { \odot } .