Statistics of magnetic field measurements and evolution of magnetic field of OBA stars

TL;DR

This paper reviews magnetic field measurements of OBA stars, confirms their distribution follows a lognormal law similar to neutron stars, and models their magnetic evolution, suggesting slow magnetic field evolution and PMS conditions influence magnetic star fractions.

Contribution

It provides the first comprehensive analysis of magnetic field distributions in OBA stars and models their evolution, linking stellar magnetic properties to initial conditions.

Findings

Magnetic fields of OBA stars follow a lognormal distribution.

Magnetic field evolution in massive stars is slow or negligible.

No evidence of a magnetic desert in the distribution.

Abstract

We review the measurements of magnetic fields of OBA stars. Based on these data we confirm that magnetic fields are distributed according to a lognormal law with a mean log(B)=-0.5 (B in kG) with a standard deviation sigma=0.5. The shape of the magnetic field distribution is similar to that for neutron stars. This finding is in favor of the hypothesis that the magnetic field of a neutron star is determined mainly by the magnetic field of its predecessor, the massive OB star. Further, we model the evolution of an ensemble of magnetic massive stars in the Galaxy. We use our own population synthesis code to obtain the distribution of stellar radii, ages, masses, temperatures, effective magnetic fields and magnetic fluxes from the pre-main sequence (PMS) via zero age main sequence (ZAMS) up to the terminal age main sequence (TAMS) stages. A comparison of the obtained in our model magnetic field distribution (MFD) with that obtained from the recent measurements of the stellar magnetic field allows us to conclude that the evolution of magnetic fields of massive stars is slow if not absent. The shape of the real MFD shows no indications of the magnetic desert proposed previously. Based on this finding we argue that the observed fraction of magnetic stars is determined by physical conditions at the PMS stage of stellar evolution.