  Determining accurate effective temperatures of stars buried in the
dust-obscured Galactic regions is extremely difficult from photometry.
Fortunately, high-resolution infrared spectroscopy is a powerful tool for
determining the temperatures of stars with no dependence on interstellar
extinction. It has long been known that the depth ratios of
temperature-sensitive and relatively insensitive spectral lines are excellent
temperature indices. In this work, we provide the first extensive line depth
ratio (LDR) method application in the infrared region that encompasses both \H\
and \K\ bands (1.48 $\mu$m - 2.48 $\mu$m). We applied the LDR method to
high-resolution (R $\simeq$ 45,000) \H\ and \K-band spectra of 110 stars
obtained with the Immersion Grating Infrared Spectrograph (IGRINS). Our sample
contained stars with 3200 $<$ \teff\ (K) $<$ 5500, 0.20 $\leq$ log g $<$ 4.6,
and $-$1.5 $<$ [M/H] $<$ 0.5. Application of this method in the \K-band yielded
21 new LDR$-$\teff\ relations. We also report five new LDR$-$\teff\ relations
found in the \H-band region, augmenting the relations already published by
other groups. The temperatures found from our calibrations provide reliable
temperatures within $\sim$70 K accuracy compared to spectral \teff\ values from
the literature.

Solar and Stellar Astrophysics;Astrophysics of Galaxies