Ba II line at 4554 Å. In the upper panels, we show the observed spectra with a black line. The blue lines are the synthetic spectra obtained with an r-process isotopic composition of barium. The red lines are the synthetic spectra obtained with an s-process composition. In the lower panels, the residual for both synthetic spectra are reported. In the left panels, we present the results for HD 6268, and on the right we show those for HD 4306.