Left: electron temperatures and densities that fit the ratios between the 1.069 μm line and all other lines at a 1σ level (colored contours, wavelengths labeled). The lines are color coded to match the spectra in the right panel. The green fill in between the green contours is an example of how to read the contour plot; the filled region covers the best-fitting set of n_e and T_e for the 1.07 μm line ratio. Other contours are not filled, but the tickmarks point downhill. The gray contour indicates where the non-detection at 1.0544 μm is matched. The black contours are the 1, 2, and 3σ confidence intervals on the best-fit to the combined lines. Right: continuum subtracted spectra of the six main C⁰ transition clusters and the non-detections at 0.985 and 1.0544 μm, normalized to the flux at 1.0694 μm, in DO Tau. Model fits for T_e = 5750 K and n_e = 6.3 × 10¹² cm⁻³ are overplotted. The spectra are color-coded to match the 1σ line ratios regions in the left panel.