Spectral average templates of 1–2.5 micron SpeX prism spectra of optically-classified field L dwarfs. Each of the three bands (JHK) are normalized across the whole band and plotted individually to remove the effect of the overall slope (color-term) of the spectrum. This allows the spectral features to be compared more directly.
The spectral features from L0 to L5 change gradually in the same direction, making a nice sequence in all three bands. The spectral features in the later type objects (L6–L8), however, do not follow the same trends as the earlier type objects and are therefore plotted separately.
The Planck functions for 2000, 1800, and 1600 K are shown (with arbitrary normalization) as dotted lines on the L0–L5 sequence. While molecular effects dominate the spectral morphology at most wavelengths, the shape of the J-band peak at 1.3 microns seems to be most sensitive to the underlying temperature-dependent Planck function rather than the strength of a particular absorption feature. It also looks like the slope of the H-band spectrum on either side of the water bands could also be modulated by the underlying Planck function rather than the water absorption itself.