High-resolution transmission spectroscopy of KELT-18b. Metastable helium detection at 1083 nm
Exoplanets orbiting near their host stars experience intense irradiation, which can drive the expansion and escape of their upper atmospheres. The near-infrared metastable helium triplet at 1083.3 nm has emerged as a powerful diagnostic to probe these mass-loss processes. We present the first high-resolution transmissi...