# Spectral Calibration of K$-$M Giants from medium resolution near-infrared HK-band spectra

## TL;DR

This study provides new medium-resolution near-infrared spectra of K-M giants and establishes empirical relations between spectral features and stellar parameters, improving temperature and gravity estimates.

## Contribution

It introduces calibrated empirical relations linking spectral line equivalent widths to stellar parameters using new and archival spectra, enhancing parameter determination accuracy.

## Key findings

- $^{12}$CO bands are good temperature indicators above 3400 K.
- Surface gravity significantly improves the empirical relations.
- Calibrated relations are based on 107 giant spectra.

## Abstract

We present here new medium resolution spectra ($\lambda/\Delta\lambda$ $\sim$ 1200) of K$-$M giants covering wavelength range 1.50$-$1.80 and 1.95$-$2.45 $\mu$m. The sample includes 72 K0$-$M8 giants from our TIRSPEC observations and all available 35 giants in that spectral range from archival IRTF spectral library. We have calibrated here the empirical relations between fundamental parameters (e.g., effective temperature, surface gravity) and equivalent widths of some important spectral features like Si I, Na I, Ca I, $^{12}$CO. We find that the $^{12}$CO first overtone band at 2.29 $\mu$m and second overtone band at 1.62 $\mu$m are a reasonably good indicator of temperature above 3400 K and surface gravity. We show that the dispersion of empirical relations between $^{12}$CO and $T_{eff}$ significantly improve considering the effect of surface gravity.