A high-resolution spectropolarimetric survey of Herbig Ae/Be stars★ – II. Rotation

Abstract

We report the analysis of the rotational properties of our sample of Herbig\nAe/Be (HAeBe) and related stars for which we have obtained high-resolution\nspectropolarimetric observations. Using the projected rotational velocities\nmeasured at the surface of the stars, we have calculated the angular momentum\nof the sample and plotted it as a function of age. We have then compared the\nangular momentum and the vsini distributions of the magnetic to the\nnon-magnetic HAeBe stars. Finally we have predicted the vsini of the\nnon-magnetic, non-binary ("normal") stars in our sample when they reach the\nZAMS, and compared them to various catalogues of the vsini of main-sequence\nstars. First, we observe that magnetic HAeBe stars are much slower rotators\nthan normal stars, indicating that they have been more efficiently braked than\nthe normal stars. In fact, the magnetic stars have already lost most of their\nangular momentum, despite their young ages (lower than 1 Myr for some of them).\nSecondly, our analysis suggests that the low mass (1.5 < M < 5 Msun) normal\nHAeBe stars evolve with constant angular momentum towards the ZAMS, while the\nhigh-mass normal HAeBe stars (M > 5 Msun) are losing angular momentum. We\npropose that winds, which are expected to be stronger in massive stars, are at\nthe origin of this phenomenon.\n