Magnetic activity of the pre-main sequence herbig Ae/Be stars

As potential progenitors of the Ap stars, the pre-main sequence intermediate mass Herbig Ae/Be stars present us with the opportunity to investigate the early history of magnetic fields at these masses. Although we have no direct evidence for the presence of magnetic fields in these stars (except in one case), many clues for such fields have been identified in the past years. They include active phenomena which are often attributed to surface magnetic fields. Rotational modulation of spectral lines formed at the photosphere and in the wind of these stars constitutes yet another indication for the presence of such fields. Future prospects for the detection and mapping of hypothetical magnetic fields in Herbig Ae/Be stars are very encouraging, and in particular spectropolarimetric observations of these stars with instruments like Espadons on CFHT will allow us to test the hypothesis that magnetic fields similar to those found on Ap stars are indeed present in these pre-main sequence objects.