Dynamo processes in the T Tauri star V410 Tau

We present new brightness and magnetic images of the weak-line T Tauri star V410 Tau, made by using data from the Narval spectropolarimeter at Telescope Bernard Lyot (TBL). The brightness image shows a large polar spot and significant spot coverage at lower latitudes. The magnetic maps show a field that is predominantly dipolar and non-axisymmetric with a strong azimuthal component. The field is 50 per cent poloidal and 50 per cent toroidal, and very little differential rotation is apparent from the magnetic images. A photometric monitoring campaign on this star has previously revealed V-band variability of up to 0.6 mag, but in 2009 the light curve is much flatter. The Doppler image presented here is consistent with this low variability. Calculating the flux predicted by the mapped spot distribution gives a peak-to-peak variability of 0.04 mag. The reduction in the amplitude of the light curve, compared with previous observations, appears to be related to a change in the distribution of the spots rather than the number or area. This paper is the first from a Zeeman-Doppler imaging campaign being carried out on V410 Tau between 2009 and 2012 at the TBL. During this time, it is expected that the light curve will return to a high-amplitude state, allowing us to ascertain whether the photometric changes are accompanied by a change in the magnetic field topology.