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

TL;DR

This study investigates the rotational properties of Herbig Ae/Be stars, revealing magnetic stars are slower rotators due to efficient braking, and high-mass stars lose angular momentum likely via stellar winds.

Contribution

It provides new insights into the rotational evolution of Herbig Ae/Be stars, especially comparing magnetic and non-magnetic stars and their angular momentum changes.

Findings

Magnetic HAeBe stars are significantly slower rotators than non-magnetic stars.

Low-mass normal HAeBe stars maintain constant angular momentum towards ZAMS.

High-mass normal HAeBe stars lose angular momentum, likely due to stellar winds.

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 vsini distributions of the magnetic to the non-magnetic HAeBe stars. Finally we have predicted the vsini of the non-magnetic, non-binary ("normal") stars in our sample when they reach the ZAMS, and compared them to various catalogues of the vsini 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 angular 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 Msun) normal HAeBe stars evolve with constant angular momentum towards the ZAMS, while the high-mass normal HAeBe stars (M > 5 Msun) are losing angular momentum. We propose that winds, which are expected to be stronger in massive stars, are at the origin of this phenomenon.