Relation between the flux ratio of C₂H₂ to H₂O as a function of stellar luminosity. Objects with M_*>0.2 M_⊙ are shown in blue and represent our T Tauri sample, and those with stellar masses below 0.2 M_⊙ are our VLMS sample and are shown in red. The two outliers around L_* ~ 1 L_⊙ are DL Tau and V1094 Sco, which will be analyzed in detail in Tabone et al. (in prep.). This trend is statistically significant with a p-value of 1.3×10⁻⁷ and a correlation coefficient of −0.77. 3σ upper and lower limits are the downward and upward triangles, respectively. The error bars are smaller than the points for most targets.