Observed and synthetic spectra around the Sr lines at 4077 Å and 4215 Å  and the G band for the s-rich star #2505. In each panel the points represent the observed spectrum, and the continuous lines are the synthesis computed with different strontium and carbon abundances. The magenta line is the spectrum computed with no contribution from Sr ii and C; the red line is the best-fitting synthesis (with the abundances given in Table 3); and the green and blue lines are the syntheses computed with Sr and C abundances altered by  ± 0.3 dex from the best value.