  We have studied the magnetic field of about 50 active and non-active single
G-K-type red giants by means of spectropolarimetry with Narval and ESPaDOnS. 30
giants have been significantly Zeeman-detected. A close study of the 17 giants
with known rotational periods shows that the measured magnetic field strength
is correlated to the rotation, in particular to the Rossby number. 4 giants for
which the magnetic field is measured to be outstandingly strong with respect to
the rotational period or the evolutionary state are identified as probable
Ap-star descendants. We detail their magnetic properties and propose criteria
to identify Ap-star descendants.
