Time-variable differences between H2RG readout channels in high precision spectroscopy: a case study with the Habitable-zone Planet Finder

High precision Doppler spectroscopy hinges on an accurate understanding of the wavelength-to-pixel mapping (wavelength solution) of the spectrograph, including particularly systematics related to the detector. Herein, we describe the uniformity and stability of the wavelength solution of the Habitable-zone Planet Finder (HPF), a near-infrared spectrograph that utilizes a Hawaii-2RG (H2RG) hybrid CMOS detector. We focus on time-varying discontinuities equivalent to approximately 10 m/s in the otherwise-smooth wavelength solution, corresponding to the boundaries between H2RG readout channels. This behavior is revealed by calibration with dedicated laser frequency comb and white light-illuminated Fabry-Perot systems over a ~1 year baseline. These findings will inform the usage of similar near-infrared CMOS devices for high-precision applications including Doppler exoplanet and gravitational lensing WFIRST surveys.