18.03.15 KB. Ok to add accepted version to spira

We report here the first results of a multiwavelength campaign focussing on magnetospheric accretion processes of the classical T Tauri star V2129 Oph. In this paper, we present spectropolarimetric observations collected in 2009 July with ESPaDOnS at the Canada-France-Hawaii Telescope and contemporaneous photometry secured with the SMARTS facility. Circularly polarized Zeeman signatures are clearly detected, both in photospheric absorption and accretionpowered emission lines, from time-series of which we reconstruct new maps of the magnetic field, photospheric brightness and accretion-powered emission at the surface of V2129 Oph using our newest tomographic imaging tool -to be compared with those derived from our old 2005 June data set, re-analysed in the exact same way.We find that in 2009 July, V2129 Oph hosts octupolar and dipolar field components of about 2.1 and 0.9 kG, respectively, both tilted by about 20 • with respect to the rotation axis; we conclude that the large-scale magnetic topology changed significantly since 2005 June (when the octupole and dipole components were about 1.5 and three times weaker, respectively), demonstrating that the field of V2129 Oph is generated by a non-stationary dynamo. We also show that V2129 Oph features a dark photospheric spot and a localized area of accretionpowered emission, both close to the main surface magnetic region (hosting fields of up to about 4 kG in 2009 July). We finally obtain that the surface shear of V2129 Oph is about half as strong as solar.From the fluxes of accretion-powered emission lines, we estimate that the observed average logarithmic accretion rate (in M yr −1 ) at the surface of V2129 Oph is −9.2 ± 0.3 at both epochs, peaking at −9.0 at magnetic maximum. It implies in particular that the radius at which the magnetic field of V2129 Oph truncates the inner accretion disc is 0.93 and 0.50 times the corotation radius (where the Keplerian period equals the stellar rotation

From observations collected with the ESPaDOnS spectropolarimeter at the Canada–France–Hawaii Telescope, we report the detection of Zeeman signatures on the low‐mass classical T Tauri star (cTTS) V2247 Oph. Profile distortions and circular polarization signatures detected in photospheric lines can be interpreted as caused by cool spots and magnetic regions at the surface of the star. The large‐scale field is of moderate strength and highly complex; moreover, both the spot distribution and the magnetic field show significant variability on a time‐scale of only 1 week, as a likely result of strong differential rotation. Both properties make V2247 Oph very different from the (more massive) prototypical cTTS BP Tau; we speculate that this difference reflects the lower mass of V2247 Oph. During our observations, V2247 Oph was in a low‐accretion state, with emission lines showing only weak levels of circular polarization; we nevertheless find that excess emission apparently concentrates in a mid‐latitude region of a strong radial field, suggesting that it is the footpoint of an accretion funnel. The weaker and more complex field that we report on V2247 Oph may share similarities with those of very‐low‐mass late‐M dwarfs and potentially explain why low‐mass cTTSs rotate on average faster than intermediate‐mass ones. These surprising results need confirmation from new independent data sets on V2247 Oph and other similar low‐mass cTTSs.