χ² difference between simulations of the 2010 data and the best fit without atmospheric escape as a function of the stellar wind density, assuming a constant escape rate and ionizing flux (Ṁ = 2 × 10⁹ g s^-1 and F_ion = 10  F_⊙, thick blue line). The intersection with the black dotted lines gives the proton density above which an absorption signature would have been detected at more than 1, 2 or 3σ in the 2010 observations. The upper limit on the proton density decreases with higher escape rates (Ṁ = 2 × 10¹⁰ g s^-1 and F_ion = 10  F_⊙, blue dotted line) and increases with higher ionizing fluxes (Ṁ = 2 × 10⁹ g s^-1 and F_ion = 20  F_⊙, blue dash-dotted line).