  We report here results of spectropolarimetric observations of the classical T
Tauri star DN Tau carried out (at 2 epochs) with ESPaDOnS at the
Canada-France-Hawaii Telescope within the `Magnetic Protostars and Planets'
programme. We infer that DN Tau, with a photospheric temperature of 3,950+-50
K, a luminosity of 0.8+-0.2 Lsun and a rotation period of 6.32 d, is a
~2Myr-old fully-convective 0.65+-0.05 Msun star with a radius of 1.9+-0.2 Dsun,
viewed at an inclination of 35+-10degr.
  Clear circularly-polarized Zeeman signatures are detected in both
photospheric and accretion-powered emission lines, probing longitudinal fields
of up to 1.8 kG (in the He1 D3 accretion proxy). Rotational modulation of
Zeeman signatures, detected both in photospheric and accretion lines, is
different between our 2 runs, providing further evidence that fields of cTTSs
are generated by non-stationary dynamos.
  Using tomographic imaging, we reconstruct maps of the large-scale field, of
the photospheric brightness and of the accretion-powered emission at the
surface of DN Tau at both epochs. We find that the magnetic topology is mostly
poloidal, and largely axisymmetric, with an octupolar component (of polar
strength 0.6-0.8 kG) 1.5-2.0x larger than the dipolar component (of polar
strength 0.3-0.5 kG).
  DN Tau features dominantly poleward accretion at both epochs. The large-scale
dipole component of DN Tau is however too weak to disrupt the surrounding
accretion disc further than 65-90% of the corotation radius (at which the disc
Keplerian period matches the stellar rotation period), suggesting that DN Tau
is already spinning up despite being fully convective.
