Surface magnetic fields on two accreting T Tauri stars: CV Cha and CR Cha

Abstract

We have produced brightness and magnetic field maps of the surfaces of CV Cha and CR Cha: two actively accreting G and K-type T Tauri stars in the Chamaeleon I star-forming cloud with ages of 3-5 Myr. Our magnetic field maps show evidence for strong, complex multi-polar fields similar to those obtained for young rapidly rotating main sequence stars. Brightness maps indicate the presence of dark polar caps and low latitude spots -- these brightness maps are very similar to those obtained for other pre-main sequence and rapidly rotating main sequence stars. Only two other classical T Tauri stars have been studied using similar techniques so far: V2129 Oph and BP Tau. CV Cha and CR Cha show magnetic field patterns that are significantly more complex than those recovered for BP Tau, a fully convective T Tauri star. We discuss possible reasons for this difference and suggest that the complexity of the stellar magnetic field is related to the convection zone; with more complex fields being found in T Tauri stars with radiative cores (V2129 Oph, CV Cha and CR Cha). However, it is clearly necessary to conduct magnetic field studies of T Tauri star systems, exploring a wide range of stellar parameters in order to establish how they affect magnetic field generation, and thus how these magnetic fields are likely to affect the evolution of T Tauri star systems as they approach the main sequence.