ISAAC J-band spectrum of J0538−0213 (black) is shown in comparison with field T dwarfs from the literature (green): 2MASS J05591914−1404488 (T4.5, Cushing et al. 2005), SDSS J212413.89+010000.3 (T5, Chiu et al. 2006), and 2MASS J09373487+2931409 (T6, Knapp et al. 2004). The T4.5 field dwarf has a similar spectral resolution to our data, while the other two field dwarfs have lower spectral resolution. The most prominent features are indicated at the top. We note that the K i doublet at around 1.25 μm is detected in J0538−0213, whose spectrum is shown with a smoothing of 3 pixels. All spectra are normalized to unity at 1.28–1.32 μm. A constant offset of 1.5 and 3.0 was added for clarity.