Simulating the 10% Incidence of Magnetic Massive Stars with Population Synthesis

Stellar magnetic fields in intermediate-mass and massive stars remain an enigma in astronomy. Observational surveys find approximately 10% of galactic stars of spectral types O and B exhibit globally organized magnetic fields without any apparent relationship with their stellar or rotational parameters. These magnetic fields are considered fossil, meaning they are purely dissipative, unlike dynamo-generated in lower mass stars. Fossil magnetic fields of massive stars significantly change the evolutionary track due to magnetic braking and mass-loss quenching. We present our results of generating a synthetic star cluster in two different star formation schemes: starburst and constant formation. The populations evolve following MESA models that account for the effects of magnetic braking, solid body rotation, and mass loss quenching. We assigned values for the initial magnetic fields using a log base 10 normal distribution. Using current observational estimates of spectropolarimetric measurements, we inferred how many stars of our simulated population would have a detectable magnetic field. Our results show that higher temperatures and more luminous stars have magnetic fields that are easier to detect than their counterparts in both the starburst and constant star formation regimes. We demonstrate that a significant portion of stars falls under the non-detection threshold, where the detectable incidence of massive stars is around 8% lower than the true magnetic incidence of the population. Our work indicates that the true number of magnetic massive stars might be greater than previously thought and presents a possible way of recreating the 10% incidence of magnetic massive stars.