Magnetism and rotation in Herbig Ae/Be stars

TL;DR

This study investigates the magnetic fields and rotational properties of Herbig Ae/Be stars during their pre-main sequence phase to understand the origin of magnetism and slow rotation in intermediate-mass stars.

Contribution

It presents observational results from a spectropolarimetric survey of about 50 Herbig Ae/Be stars, shedding light on magnetic field origins and rotational evolution.

Findings

Detection of magnetic fields in a subset of Herbig Ae/Be stars.

Evidence supporting the fossil origin hypothesis of stellar magnetic fields.

Insights into magnetic braking effects during the PMS phase.

Abstract

Among the main sequence intermediate mass A and B stars, around 5% host large-scale organized magnetic fields. Most of these stars are very slow rotators compared to their non-magnetic counterparts, and show photospheric abundance anomalies. They are referred to as the Ap/Bp stars. One of the greatest challenges, today is to understand the origin of their magnetic field and their slow rotation. The favoured hypothesis is a fossil origin of the magnetic field, in which the magnetic fields of Ap/Bp stars are relics of those which existed in the parental molecular clouds during the formation. This implies that the magnetic field must survive all the initial phases of the stellar evolution and especially the pre-main sequence (PMS) phase. This is consistent with the general belief that magnetic braking occurs during the PMS phase, which sheds angular momentum and slows the rotation of these stars. In this context, we proceeded with a survey of a sample of around 50 PMS Herbig Ae/Be stars, using the new spectropolarimeter ESPaDOnS at the CFHT, in order to study the magnetic field and the rotation velocity of these stars. This talk reviews the results of our survey, as well as their consequences for the origin of the magnetic fields and the evolution of the rotation of intermediate mass stars during the PMS phase.