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

Abstract

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 $\mu$m) with the SpeX spectrograph. The spectrum of GJ 660.1B is distinctly peculiar, with a triangular-shaped 1.7 $\mu$m 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$\pm$0.5 cgs) and very low metallicity ([M/H] = $-$0.96${}_{-0.24}^{+0.19}$), or high surface gravity ($\log g$ = 5.0-5.5) and slightly subsolar metallicity ([M/H] =$-$0.20${}_{-0.19}^{+0.13}$). We conjecture that insufficient condensate opacity and excessive collision induced H${}_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.

11 pages, 15 figures, accepted for publication to AJ

References in corpus (23)

• The 0.8-14.5 micron Spectra of Mid-L to Mid-T Dwarfs: Diagnostics of Effective Temperature, Grain Sedimentation, Gas Transport, and Surface Gravity
• Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime
• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life
• A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• Subtle Signatures of Multiplicity in Late-type Dwarf Spectra: The Unresolved M8.5 + T5 Binary 2MASS J03202839-0446358
• Consistent simulations of substellar atmospheres and non-equilibrium dust-cloud formation
• HD 203030B: an Unusually Cool Young Sub-Stellar Companion near the L/T Transition
• Clouds, Gravity and Metallicity in Blue L dwarfs: The Case of 2MASS J11263991-5003550
• SpeX Spectroscopy of Unresolved Very Low Mass Binaries. II. Identification of Fourteen Candidate Binaries with Late-M/Early-L and T Dwarf Components
• Physical parameters of two very cool T dwarfs
• Optical Spectroscopy of 2MASS Color-Selected Ultracool Subdwarfs
• HD3651B: the first directly imaged brown dwarf companion of an exoplanet host star
• Stellar parameters of early M dwarfs from ratios of spectral features at optical wavelengths
• Wide, Cool and Ultracool Companions to Nearby Stars from Pan-STARRS1
• Keck Laser Guide Star Adaptive Optics Monitoring of the M8+L7 Binary LHS 2397aAB: First Dynamical Mass Benchmark at the L/T Transition
• Cool Subdwarf Investigations (CSI) I: New Thoughts for the Spectral Types of K and M Subdwarfs
• Discovery of the Coolest Extreme Subdwarf
• WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun
• Trigonometric parallaxes of ten ultracool subdwarfs
• Halo Stars Near the Hydrogen-Burning Limit: The M/L Subdwarf Transition
• Optical and Near-Infrared Spectroscopy of the L Subdwarf SDSS J125637.13-022452.4

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