2017ApJS..230...23V

We present a 0.7-2.5 µm spectral library of 284 stars observed with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Maunakea, Hawaii. This library extends the metallicity range of the IRTF Cool Star library beyond solar metallicity to -1.7 < [Fe/H] < 0.6. All of the observed stars are also in the MILES optical stellar library, providing continuous spectral coverage for each star from 0.35 to 2.5 µm. The spectra are absolute flux calibrated using Two Micron All Sky Survey photometry, and the continuum shape of the spectra is preserved during the data reduction process. Synthesized JHK_S colors agree with observed colors at the 1%-2% level, on average. We also present a spectral interpolator that uses the library to create a data-driven model of spectra as a function of T_eff, log g, and [Fe/H]. We use the library and interpolator to compare empirical trends with theoretical predictions of spectral feature behavior as a function of stellar parameters. These comparisons extend to the previously difficult to access low-metallicity and cool dwarf regimes, as well as the previously poorly sampled super-solar metallicity regime. The library and interpolator are publicly available.