The time evolution of angular momentum and surface rotation of massive stars are strongly influenced by fossilmagnetic fields viamagnetic braking.We present a new module containing a simple, comprehensive implementation of such a field at the surface of a massive star within theModules for Experiments in Stellar Astrophysics (MESA) software instrument.We test two limiting scenarios for magnetic braking: distributing the angular momentum loss throughout the star in the first case, and restricting the angular momentum loss to a surface reservoir in the second case.We perform a systematic investigation of the rotational evolution using a grid of OB star models with surface magnetic fields (M∗ = 5-60 M⊙, Ω/Ωcrit = 0.2-1.0, Bp = 1-20 kG). We then employ a representative grid of B-type star models (M∗ = 5, 10, 15 M⊙, Ω/Ωcrit =0.2, 0.5, 0.8, Bp =1, 3, 10, 30 kG) to compare to the results of a recent self-consistent analysis of the sample of known magnetic B-type stars. We infer that magnetic massive stars arrive at the zero-age main sequence (ZAMS) with a range of rotation rates, rather than with one common value. In particular, some stars are required to have close-to-critical rotation at the ZAMS. However, magnetic braking yields surface rotation rates converging to a common low value, making it difficult to infer the initial rotation rates of evolved, slowly rotating stars.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science