  Application of the radial velocity (RV) technique in the near infrared is
valuable because of the diminished impact of stellar activity at longer
wavelengths, making it particularly advantageous for the study of late-type
stars but also for solar-type objects. In this paper, we present the IGRINS RV
open source python pipeline for computing infrared RV measurements from reduced
spectra taken with IGRINS, a R ~ 45,000 spectrograph with simultaneous coverage
of the H band (1.49--1.80 $\mu$m) and K band (1.96--2.46 $\mu$m). Using a
modified forward modeling technique, we construct high resolution telluric
templates from A0 standard observations on a nightly basis to provide a source
of common-path wavelength calibration while mitigating the need to mask or
correct for telluric absorption. Telluric standard observations are also used
to model the variations in instrumental resolution across the detector,
including a yearlong period when the K band was defocused. Without any
additional instrument hardware, such as a gas cell or laser frequency comb, we
are able to achieve precisions of 26.8 $\rm m\,s^{-1}$ in the K band and 31.1
$\rm m\,s^{-1}$ in the H band for narrow-line hosts. These precisions are
empirically determined by a monitoring campaign of two RV standard stars as
well as the successful retrieval of planet-induced RV signals for both HD
189733 and $\tau$ Boo A; furthermore, our results affirm the presence of the
Rossiter-McLaughlin effect for HD 189733. The IGRINS RV pipeline extends
another important science capability to IGRINS, with publicly available
software designed for widespread use.
