A high-resolution spectropolarimetric survey of Herbig Ae/Be stars
I. Rotation

E. Alecian, G.A. Wade, C. Catala, J.H. Grunhut, J.D. Landstreet, S. Bagnulo, T. Böhm, C.P. Folsom, S. Marsden, I. Waite

Figure 1. Magnetic (red squares) and non-magnetic (black points) Herbig Ae/Be stars plotted in a Hertzsprung-Russell diagram. Open circles correspond to HD 98922 (above the birthline) and IL Cep (below the ZAMS) that fall outside of the PMS region of the HR diagram, whose positions cannot be reproduced with the theoretical evolutionary tracks considered in this paper. The CESAM PMS evolutionary tracks for 1.5, 3, 6, 9 and 15 M (black full lines), 0.01, 0.1, 1 and 10 Myr isochrones (blue thin dashed lines), and the ZAMS (black dot-dashed line) are also plotted. The birthline taken from Behrend & Maeder (2001) is plotted with a blue thick dashed line. The convective/radiative phase transition is overplotted with an orange dot-dot-dot-dashed line.

Abstract

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

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Last Revised: 2012 November 20th