CCF for CO₂ on TRAPPIST-1 e corresponding to 40 stacked transits, fitted with two different models. Top: Gaussian + constant baseline fitted by bounded nonlinear least-squares (trust region reflective algorithm), minimizing the sum of squared residuals. It fails to capture the secondary lobes. Bottom: posterior predictive mean of the signal model, from our Bayesian framework. The molecule-specific kernel captures the full shape of the CCF, outperforming the simple Gaussian model.