The GAPS Programme at TNG

Context . Atmospheric escape plays a fundamental role in shaping the properties of exoplanets. The metastable near-infrared (nIR) helium triplet at 1083.3 nm (He I ) is a powerful proxy of extended and evaporating atmospheres. Aims . We used the GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio Nazionale Galileo to search for He I absorption in the upper atmospheres of five close-in giant planets hosted by the K and M dwarf stars of our sample, namely WASP-69 b, WASP-107 b, HAT-P-11 b, GJ 436 b, and GJ 3470 b. Methods . We focused our analysis on the nIR He I triplet, performing high-resolution transmission spectroscopy by comparing the in-transit and out-of-transit observations. In instances where nightly variability in the He I absorption signal was identified, we investigated the potential influence of stellar magnetic activity on the planetary absorption signal by searching for variations in the H α transmission spectrum. Results . We spectrally resolve the He I triplet and confirm the published detections for WASP-69 b (3.91 ± 0.22%, 17.6 σ ), WASP-107 b (8.17 −0.76 +0.80 %, 10.5 σ ), HAT-P-11 b (1.36 ± 0.17%, 8.0 σ ), and GJ 3470 b (1.75 −0.36 +0.39 %, 4.7 σ ). We do not find evidence of extra absorption for GJ 436 b. We observe night-to-night variations in the He I absorption signal for WASP-69 b, associated with variability in H α , which likely indicates the influence of pseudo-signals related to stellar activity. Additionally, we find that the He I signal of GJ 3470 b originates from a single transit observation, thereby corroborating the discrepancies found in the existing literature. An inspection of the H α line reveals an absorption signal during the same transit event. Conclusions . By combining our findings with previous analyses of GIANO-B He I measurements of planets orbiting K dwarfs, we explore potential trends with planetary and stellar parameters that are thought to affect the absorption of metastable He I . Our analysis is unable to identify clear patterns, thus emphasising the necessity for additional measurements and the exploration of potential additional parameters that may be important in controlling He I absorption in planetary upper atmospheres.