3D MHD simulations and synthetic radio emission from an oblique rotating magnetic massive star (1907.07068v1)

Abstract: We have performed 3D isothermal MHD simulation of a magnetic rotating massive star with a non-zero dipole obliquity and predicted the radio/sub-mm observable lightcurves and continuum spectra for a frequency range compatible with ALMA. From these results we also compare the model input mass-loss to that calculated from the synthetic thermal emission. Spherical and cylindrical symmetry is broken due to the obliquity of the stellar magnetic dipole resulting in an inclination and phase dependence of both the spectral flux and inferred mass-loss rate, providing testable predictions of variability for oblique rotator. Both quantities vary by factors between 2 and 3 over a full rotational period of the star, demonstrating that the role of rotation as critical in understanding the emission. This illustrates the divergence from a symmetric wind, resulting in a two armed spiral structure indicative of a oblique magnetic rotator. We show that a constant spectral index, $\alpha$, model agrees well with our numerical prediction for a spherical wind for $\nu~<~10^{3} \ \mathrm{GHz}$, however it is unable to capture the behavior of emission at $\nu~>~10^{3} \ \mathrm{GHz}$. As such we caution the use of such constant $\alpha$ models for predicting emission from non-spherical winds such as those which form around magnetic massive stars.