  Seismic observations have shown that a number of evolved stars exhibit
low-amplitude dipole modes, which are referred to as depressed modes. Recently,
these low amplitudes have been attributed to the presence of a strong magnetic
field in the stellar core of those stars.
  We intend to study the properties of depressed modes in evolved stars, which
is a necessary condition before concluding on the physical nature of the
mechanism responsible for the reduction of the dipole mode amplitudes.
  We perform a thorough characterization of the global seismic parameters of
depressed dipole modes and show that these modes have a mixed character. The
observation of stars showing dipole mixed modes that are depressed is
especially useful for deriving model-independent conclusions on the dipole mode
damping.
  Observations prove that depressed dipole modes in red giants are not pure
pressure modes but mixed modes. This result invalidates the hypothesis that the
depressed dipole modes result from the suppression of the oscillation in the
radiative core of the stars. Observations also show that, except for the
visibility, the seismic properties of the stars with depressed modes are
equivalent to those of normal stars.
  The mixed nature of the depressed modes in red giants and their unperturbed
global seismic parameters carry strong constraints on the physical mechanism
responsible for the damping of the oscillation in the core. This mechanism is
able to damp the oscillation in the core but cannot fully suppress it.
Moreover, it cannot modify the radiative cavity probed by the gravity component
of the mixed modes. The recent mechanism involving high magnetic field proposed
for explaining depressed modes is not compliant with the observations and
cannot be used to infer the strength and the prevalence of high magnetic fields
in red giants.
