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We present spectroscopic analysis of the low mass binary star system GJ660.1AB, a pair of nearby M dwarfs for which we have obtained separatednear-infrared spectra (0.9-2.5 $\mu$m) with the SpeX spectrograph. The spectrumof GJ 660.1B is distinctly peculiar, with a triangular-shaped 1.7 $\mu$m peakthat initially suggests it to be a low surface gravity, young brown dwarf.However, we rule out this hypothesis and determine instead that this companionis a mild subdwarf (d/sdM7) based on the subsolar metallicity of the primary,[Fe/H] = $-$0.63$\pm$0.06. Comparison of the near-infrared spectrum of GJ660.1B to two sets of spectral models yields conflicting results, with a commoneffective temperature T$_{eff}$ = 2550-2650 K, but alternately low surfacegravity ($\log{g}$ = 4.4$\pm$0.5 cgs) and very low metallicity ([M/H] =$-$0.96$^{+0.19}_{-0.24}$), or high surface gravity ($\log{g}$ = 5.0-5.5) andslightly subsolar metallicity ([M/H] =$-$0.20$^{+0.13}_{-0.19}$). We conjecturethat insufficient condensate opacity and excessive collision induced H$_2$absorption in the models bias them toward low surface gravities and ametallicity inconsistent with the primary, and points toward improvementsneeded in the spectral modeling of metal-poor, very-low mass dwarfs. Thepeculiar spectral characteristics of GJ 660.1B emphasize that care is neededwhen interpreting surface gravity features in the spectra of ultracool dwarfs.

Characterization of the Very Low Mass Secondary in the GJ 660.1AB System