Challenges in high-resolution near-infrared spectroscopy

High-resolution near-infrared spectrographs open the door to exciting science in a variety of domains of astrophysics. These spectrographs have a number of peculiarities compared with optical spectrographs at comparable resolution. These challenges come from two main sources, telluric (both emission and absorption) and instrumental (detector, fibre properties). Telluric absorption correction at high accuracy is notoriously challenging, and correction at a sub-percent accuracy requires accounting for higher-order terms not captured by atmospheric models. Sky emission is simpler to model with a sky fibre correction but nonetheless requires careful error and noise propagation as well as the inclusion of thermal background emission in the K band and beyond. Infrared arrays are now available in large format (4k4k arrays). Still, their cosmetics and noise properties differ significantly from those of CCDs and affect spectra at the pixel level and on large spectral scales. Furthermore, precision radial velocity is a key aspect of nIR high-resolution spectroscopy, but it must account for systematics at a level significantly larger than equivalent observations in the optical domain. I will present a review of these challenges, solutions, and insight gained from the NIRPS spectrograph recently commissioned at the La Silla 3.6m telescope.