  One interpretation of the activity and magnetism of late-type stars is that
these both intensify with decreasing Rossby number up to a saturation level,
suggesting that stellar dynamos depend on both rotation and convective
turbulence. Some studies have claimed, however, that rotation alone suffices to
parametrise this scaling adequately. Here, we tackle the question of the
relevance of turbulence to stellar dynamos by including evolved, post main
sequence stars in the analysis of the rotation-activity relation. These stars
rotate very slowly compared with main sequence stars, but exhibit similar
activity levels. We show that the two evolutionary stages fall together in the
rotation-activity diagram and form a single sequence in the unsaturated regime
in relation only to Rossby numbers derived from stellar models, confirming
earlier preliminary results that relied on a more simplistic parametrisation of
the convective turnover time. This mirrors recent results of fully convective M
dwarfs, which likewise fall on the same rotation-activity sequence as partially
convective solar-type stars. Our results demonstrate that turbulence plays a
crucial role in driving stellar dynamos and suggest that there is a common
turbulence-related dynamo mechanism explaining the magnetic activity of all
late-type stars.
