Normalized observational spectra (black solid curves). A straight line continuum was defined over the 3960–4000 Å range of each spectrum still in the observer rest frame. The top panel includes a synthetic A₁ band of C₆₀ with expected position and width, and arbitrary equivalent width (thick gray solid curve). Its position is indicated through all panels (vertical dotted line). The light gray area indicates the wavelength interval of two FWHMs taken into account to evaluate ^uW(C₆₀, A₁) at 3980 Å for each LOS. The spectral type of each target star is indicated.