Computational models of stars, also called stellar models, predict the fundamental properties (e.g., radius, surface temperature, and brightness) of stars based on their age. Comparing stellar model predictions to properties of real stars allows astronomers to estimate stellar ages, which are key constraints on planet formation theories. However, existing stellar models are known to be inaccurate; real stars are cooler and larger than model predictions [1]. As a result, ages inferred from stellar models are also inaccurate. Notably, models have the greatest difficulty accurately predicting properties of stars that are magnetically active, suggesting magnetic fields are responsible for the disagreements. To test this hypothesis, we computed a large a grid of stellar models including effects from magnetic fields that, for the first time, include a magnetic field that adjusts with the model star's age. Our models confirm earlier results that strong magnetic fields can cause stars to become cooler and larger [1]. However, we expand on current knowledge by calculating the maximum changes that can be reasonably be expected to a star's surface temperature and radius throughout a star's life due solely to magnetic fields. Our results suggest that magnetic fields partially explain the observed disagreements between models and real stars, but ultimately provide an incomplete picture. Nevertheless, our model grid will permit more rigorous tests of the magnetic field hypothesis that may lead to more accurate stellar ages and a better understanding of planet formation processes.
[1]Feiden, G. (2015). Stellar Evolution Models of Young Stars: Progress and Limitations. Proceedings of the International Astronomical Union, 10(S314), 79-84. doi:10.1017/S1743921315006067