Evolution of Magnetic Fields of Herbig Ae/Be Stars

Abstract

Magnetic-field measurements for Herbig Ae/Be stars are analyzed to determine the distribution functions of root-mean-squared magnetic field strengths \(\mathcal{B}\) (in G) and magnetic fluxes Φ (in G cm²) for Herbig stars with measured magnetic field. The \(\mathcal{B}\) and Φ values are approximated by log-normal functions with the means equal to 〈log \(\mathcal{B}\)〉 = 2.0 and log 〈Φ Φ〉 = 25.5, respectively, and with the widths of \({\rm{log}}(\sigma)_\mathcal{B}=0.3\) dex and log(σ_Φ) = 0.4 dex, respectively. The inferred distribution widths are close to the typical values for main-sequence (MS) AB-type stars, whereas the mean logarithms of magnetic fields and magnetic fluxes proved to be significantly (by up to one order of magnitude) lower than the corresponding values for MS stars (2.5 and 26.4, respectively). The origin of these differences and the evolution of magnetic fields for intermediate-mass pre-MS stars are discussed.