The GAPS Programme at TNG. LXXXI. The puzzle of the HeI absorption signal in the atmosphere of V1298Taub with GIARPS@TNG

Atmospheric escape shapes the mass, radius, and atmospheric composition of close-in planets, primarily over their first tens of Myr. The young system (10,--,30 Myr) represents a benchmark for investigating photoevaporation and planetary evolution at early stages of a system's existence. The metastable ̋ei near-infrared triplet is a key proxy for exoplanetary atmospheric escape. We aim to detect and characterise ̋ei in the extended atmosphere of We analysed four transits spanning a four-year baseline using the GIARPS (GIANO-B + HARPS-N) observing mode at the Telescopio Nazionale . We re-derived the projected spin-orbit angle by modelling the Rossiter-McLaughlin effect. Using the simultaneous optical and near-infrared high-resolution transmission spectroscopy of ) to disentangle stellar activity from planetary evaporation. Galileo we monitored the ̋ei triplet alongside key chromospheric indicators (łogrhk, ̋a, and Na i While the stellar spectra show significant night-to-night variability, transmission spectroscopy reveals persistent absorption across all four epochs. This contrasts with optical indicators (̋a and He i Na i ), observed over the two nights with simultaneous optical monitoring, which fluctuate between emission and absorption due to stellar activity. The consistent presence of over these four years could suggest a planetary origin, despite stellar-driven depth modulation. hydrodynamic simulations show that stellar XUV flux variations significantly modulate the ̋ei absorption depth and equivalent width. Furthermore, stellar wind fluctuations likely drive the observed night-to-night variability of the exospheric structure. He i ATES The detection of ̋ei across all epochs could support the assumption of planetary evaporation, despite it being modulated by stellar activity. Our results underscore the fact that disentangling a planetary signal from stellar contamination remains a big challenge for highly active hosts. Ultimately, confirming the planetary nature of the ̋ei signature requires comprehensive activity monitoring and full transit coverage to establish a robust baseline.