The distribution of the unstable modes in the HR diagram. (a) The pulsationally unstable fundamental (large solid dots) and the first overtone (crosses); (b) the second and third overtones (large solid dots and crosses, respectively); (c) the fourth and fifth overtones (large solid dots and crosses, respectively); (d) the sixth and seventh overtones (large solid dots and crosses, respectively). The small dots are pulsationally stable models.