HR diagram of intrinsic (filled triangles) and extrinsic (open squares) S stars along with the STAREVOL evolutionary tracks corresponding to the closest grid metallicity. The red giant branch is represented by the blue dots, the core He-burning phase by the green solid line, whereas the red dashed line corresponds to the AGB tracks. HD 189581 has been moved by − 100 K to avoid overlap with the extrinsic S stars AB Col and V530 Lyr in the left panel.