We report here results of spectropolarimetric observations of the classical T Tauri star ( cTTS ) GQ Lup carried out with ESPaDOnS at the Canada-France-Hawaii Telescope ( CFHT ) in the framework of the ‘ Magnetic Protostars and Planets ’ ( MaPP ) programme , and obtained at 2 different epochs ( 2009 July and 2011 June ) .
From these observations , we first infer that GQ Lup has a photospheric temperature of 4 , 300 \pm 50 K and a rotation period of 8.4 \pm 0.3 d ; it implies that it is a 1.05 \pm 0.07 { M } _ { \odot } star viewed at an inclination of \simeq 30 ^ { \circ } , with an age of 2–5 Myr , a radius of 1.7 \pm 0.2 { R } _ { \odot } , and has just started to develop a radiative core .

Large Zeeman signatures are clearly detected at all times , both in photospheric lines and in accretion-powered emission lines , probing longitudinal fields of up to 6 kG and hence making GQ Lup the cTTS with the strongest large-scale fields known as of today .
Rotational modulation of Zeeman signatures , also detected both in photospheric and accretion proxies , is clearly different between our 2 runs ; we take this as further evidence that the large-scale fields of cTTSs are evolving with time and thus that they are produced by non-stationary dynamo processes .

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 GQ Lup at both epochs .
We find that the magnetic topology is mostly poloidal and axisymmetric with respect to the rotation axis of the star ; moreover , the octupolar component of the large-scale field ( of polar strength 2.4 and 1.6 kG in 2009 and 2011 respectively ) dominates the dipolar component ( of polar strength \simeq 1 kG ) by a factor of \simeq 2 , consistent with the fact that GQ Lup is no longer fully-convective .

GQ Lup also features dominantly poleward magnetospheric accretion at both epochs .
The large-scale dipole component of GQ Lup is however not strong enough to disrupt the surrounding accretion disc further than about half-way to the corotation radius ( at which the Keplerian period of the disc material equals the stellar rotation period ) , suggesting that GQ Lup should rapidly spin up like other similar partly-convective cTTSs .

We finally report a 0.4 km s ^ { -1 } RV change for GQ Lup between 2009 and 2011 , suggesting that a brown dwarf other than GQ Lup B may be orbiting GQ Lup at a distance of only a few au ’ s .