A Helicity-Based Method to Infer the CME Magnetic Field Magnitude in Sun and Geospace: Generalization and Extension to Sun-Like and M-Dwarf Stars and Implications for Exoplanet Habitability

摘要

Patsourakos et al. (Astrophys. J. 817, 14, 2016) and Patsourakos andGeorgoulis (Astron. Astrophys. 595, A121, 2016) introduced a method to inferthe axial magnetic field in flux-rope coronal mass ejections (CMEs) in thesolar corona and farther away in the interplanetary medium. The method, basedon the conservation principle of magnetic helicity, uses the relative magnetichelicity of the solar source region as input estimates, along with the radiusand length of the corresponding CME flux rope. The method was initially appliedto cylindrical force-free flux ropes, with encouraging results. We herebyextend our framework along two distinct lines. First, we generalize ourformalism to several possible flux-rope configurations (linear and nonlinearforce-free, non-force-free, spheromak, and torus) to investigate the dependenceof the resulting CME axial magnetic field on input parameters and the employedflux-rope configuration. Second, we generalize our framework to both Sun-likeand active M-dwarf stars hosting superflares. In a qualitative sense, we findthat Earth may not experience severe atmosphere-eroding magnetosphericcompression even for eruptive solar superflares with energies ~ 10^4 timeshigher than those of the largest Geostationary Operational EnvironmentalSatellite (GOES) X-class flares currently observed. In addition, the tworecently discovered exoplanets with the highest Earth-similarity index, Kepler438b and Proxima b, seem to lie in the prohibitive zone of atmospheric erosiondue to interplanetary CMEs (ICMEs), except when they possess planetary magneticfields that are much higher than that of Earth.