Comparison of FUOr molecular diagnostics. In the top panels, the CO 2.30 μm EW in the K band is plotted vs. FeH 1.62 μm EW in the H band (left) and vs. the H₂O 1.34 μm spectral index in the J band (right). Both plots show some overlap between FUOrs and M dwarfs, with the FUOrs tending to be slightly stronger than dwarfs and significantly weaker than giants in their molecular absorption. In the bottom panels, the H₂O 1.74 μm spectral index in the H band is plotted vs. the CO 2.30 μm EW in the K band (left) and the H₂O 1.34 μm spectral index in the J band (right).