Investigating Spectral Stability in the Vicinity of the Metastable Helium Triplet of WASP-107

Abstract I present an analysis of the stellar line variability of WASP-107, focusing on the metastable helium triplet at 1083 nm (He i *), which has become a key tracer of atmospheric escape in exoplanets. With high-resolution spectra from Canada–France–Hawaii Telescope/SPIRou collected over approximately one year. I asses the out-of-transit variability of He i * and nearby stellar features. An injection and recovery test demonstrates equivalent widths are reliably recovered above input depths of 0.005 nm, with low signal-to-noise ratios leading to slight systematic underestimation. The observed upper limit variability in three lines is 1.8%, 2.6%, and 2.0%, respectively, while nearby Mg i and Si i lines vary by 1.2%, including both stellar and instrumental effects. These results underscore the importance of quantifying variability in the triplet to accurately interpret absorption signals.