T_e(He i) vs. T_e(H i) diagram. Two methods for deriving T_e(He i) have been used. One follows the method of Zhang et al. (2005), based on the line ratio λ7281/λ6678 (open circles). The other follows the Peimbert et al. (2002) procedure and computes T_e(He i) based on several He i lines (black circles). Solid line represents equality (t² = 0), and dotted lines show the variation in T_e(H i) as a function of T_e(He i) considering different t² values.