Curve of growth for Fe ii lines using oscillator strengths from Meléndez & Barbuy (2009). Unit slope is indicated by the solid gray line. Along this line, the ordinate, and the abscissa (X), are equal. SS model curves are drawn for a = γ_λ / (2·Δλ_D) of 1, 0.1, 0.01, and 0.001 (from the top). The abscissae for the points are log (gfλ) − θ·χ. Open circles are for 2.58 ≤ χ ≤ 2.89, open squares for 3.20 ≤ χ ≤ 3.89, and filled stars for 5.51 ≤ χ ≤ 6.22 eV. The observed points have been made to coincide by adding +5.7 to the abscissa, and −0.6 to the ordinate. The latter figure is relevant for the microturbulence. This plot was made with θ = 0.7 (7200 K).