We present spectroscopic analysis of the low mass binary star system GJ 660.1AB , a pair of nearby M dwarfs for which we have obtained separated near-infrared spectra ( 0.9-2.5 \micron ) with the SpeX spectrograph .
The spectrum of GJ 660.1B is distinctly peculiar , with a triangular-shaped 1.7 \micron peak that initially suggests it to be a low surface gravity , young brown dwarf .
However , we rule out this hypothesis and determine instead that this companion is 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 GJ 660.1B to two sets of spectral models yields conflicting results , with a common effective temperature T _ { eff } = 2550–2650 K , but alternately low surface gravity ( \log { g } = 4.4 ^ { +0.5 } _ { -0.5 } ) and very low metallicity ( [ M/H ] = - 0.96 ^ { +0.19 } _ { -0.24 } ) , or high surface gravity ( \log { g } = 5.0–5.5 ) and slightly subsolar metallicity ( [ M/H ] = - 0.20 ^ { +0.13 } _ { -0.19 } ) .
We conjecture that insufficient condensate opacity and excessive collision induced H _ { 2 } absorption in the models bias them toward low surface gravities and a metallicity inconsistent with the primary , and points toward improvements needed in the spectral modeling of metal-poor , very-low mass dwarfs .
The peculiar spectral characteristics of GJ 660.1B emphasize that care is needed when interpreting surface gravity features in the spectra of ultracool dwarfs .