# The Extended IRTF Spectral Library: Expanded coverage in metallicity, temperature, and surface gravity

## TL;DR

This paper introduces an expanded infrared spectral library of 284 stars covering a broad range of metallicities, temperatures, and gravities, with a spectral interpolator for modeling stellar spectra based on these parameters.

## Contribution

The paper provides a new, extensive spectral library with improved metallicity coverage and a data-driven spectral interpolator, enhancing stellar characterization across diverse stellar types.

## Key findings

- Spectral library covers $0.7-2.5\,\mu m$ with 284 stars.
- Library extends metallicity range to $-1.7 < [Fe/H] < 0.6$.
- Spectral interpolator models spectra as a function of stellar parameters.

## Abstract

We present a $0.7-2.5\mu m$ spectral library of 284 stars observed with the medium-resolution infrared spectrograph, SpeX, at the 3.0 meter 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 $0.35-2.5\mu m$. 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 $teff$, $logg$, 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.