Observation (gray) of Hen 2−39 compared to model spectra with T_eff = 4000, 4250, 4500 K (blue, red, green) for selected regions that were used for the determination of T_eff. CN, C₂, and CH absorption lines are indicated at the bottom in green, purple, and cyan, respectively. All absorption lines that appear with an equivalent width ≥ 20 mÅ in the calculated spectrum are indicated.