JOINT HIGH- AND LOW-RESOLUTION ANALYSIS OF WASP-107B'S ATMOSPHERE: COMBINED STRENGTHS AND INTRINSIC OBSERVATIONAL LIMITS (HoRS3S)

The atmospheric characterization of Neptune-mass exoplanets serves as a crucial stepping stone toward understanding smaller, potentially habitable worlds. This study presents a comprehensive multi-resolution analysis of WASP-107b, a warm super-Neptune with an extended atmosphere ideal for transmission spectroscopy. Our purpose is to combine high-resolution (HR) ground-based observations (TNG/GIANO-B, GEMINI SOUTH/IGRINS) with low-resolution (LR) space-based data (HST/WFC3, JWST/NIRCam, JWST/ MIRI). Combining HR and LR spectroscopy provides complementary atmospheric constraints. HR resolves molecular absorption into unique line forests, disentangling overlapping spectral signatures between primary and secondary species. It probes the upper atmospheric layers and penetrates through clouds. LR preserves continuum information essential for measuring absolute abundances and probes lower atmospheric regions. This multi-resolution approach enables complete vertical atmospheric coverage while providing tighter constraints on molecular detections. We first validated previous LR studies, confirming strong spectral signatures of CO₂, CO, H₂O, and SO₂, along with weaker signatures of NH₃ and CH₄. For the HR analysis, we combined two transits from GIANO-B (0.95–2.45 μm) with three transits from IGRINS (1.45–2.45 μm), both providing R ≃ 48,000. After disentangling the planetary signal from telluric and stellar contamination using Principal Component Analysis, we applied cross-correlation techniques to assess whether LR-detected molecules are detectable at HR and to search for additional secondary species. Finally, the combined analysis is completed through a Bayesian atmospheric retrieval that simultaneously fits both datasets, leveraging their complementary capabilities to provide tighter constraints on atmospheric composition and structure. A fundamental observational challenge for this planetary class emerges from their orbital dynamics. Unlike hot Jupiters (Kp > 140 km/s), where planetary and telluric signals separate cleanly in velocity space, warm Neptunes like WASP-107b (Kp ≃ 105 km/s) experience significant velocity overlap between planetary and telluric features, limiting molecular identification at HR. This challenge becomes increasingly critical for Earth-sized and super-Earth targets. While upcoming Extremely Large Telescopes will enhance sensitivity through greater collecting power, the velocity overlap represents a fundamental systematic limitation requiring advanced techniques to disentangle planetary from stellar and telluric signals for reliable ground-based characterization of terrestrial exoplanet atmospheres.