Variation of UV spectral flux as a function of T_eff with fixed parameters (log g=3.0,[Fe/H]=−1.0). Upper row: variation for the [O/Fe] ratio of −0.2,+0.2,+0.6, and +0.8. Lower row: same as the upper row but for [Mg/Fe] ratios. The depth of the OH molecular band first increases and then decreases with rising T_eff, with the peak occurring around K-type stars (approximately 4000−5000 K). Similarly, the depth of the Mg I line increases and then decreases with rising T_eff, with the peak occurring around K-type to G-type stars (approximately 4000−5800 K), while the Mg II line continuously strengthens with increasing T_eff.