How non-magnetic are "non-magnetic" Herbig Ae/Be stars?

TL;DR

This study investigates the magnetic properties of Herbig Ae/Be stars, finding that most lack detectable magnetic fields and establishing upper limits on possible undetected dipolar fields through statistical modeling.

Contribution

It provides the first large-scale statistical analysis of magnetic fields in Herbig Ae/Be stars, setting upper limits on undetected magnetic fields in a significant sample.

Findings

Most Herbig Ae/Be stars show no detectable magnetic fields.

Upper limits on dipolar magnetic fields are established for individual stars.

Statistical modeling constrains the presence of undetected magnetic fields.

Abstract

Our recent discovery of magnetic fields in a small number of Herbig Ae/Be stars has required that we survey a much larger sample of stars. From our FORS1 and ESPaDOnS surveys, we have acquired about 125 observations of some 70 stars in which no magnetic fields are detected. Using a Monte Carlo approach, we have performed statistical comparisons of the observed longitudinal fields and LSD Stokes V profiles of these apparently non-magnetic stars with a variety of field models. This has allowed us to derive general upper limits on the presence of dipolar fields in the sample, and to place realistic upper limits on undetected dipole fields which may be present in individual stars. This paper briefly reports the results of the statistical modeling, as well as field upper limits for individual stars of particular interest.