Left panel: comparison between the observed DK Cha Brackett decrement and the expected curves for Case B recombination and black-body emission. The crosses represent the ratios from case B recombination at T = 10 000 K, n = 10¹⁰ cm^-3 (black continuous line) and T = 1000 K, n = 10¹⁰ cm^-3 (green dashed line), while dots represent the black-body curves at T = 3500 K (dashed red line). Right panel: comparison between the observed DK Cha Paschen decrement (black dots), the Paschen decrement of the CTTSs sample of Bary et al. (2008, open green squares) and the expected Paschen ratios from Case B recombination at T = 1000 K, n = 10¹⁰ cm^-3 (green dashed line).