Constraining the properties of red supergiants stars with 3D MHD models

IRC-10414 is the twince star of Betelgeuse, as (i) they are both evolved massive stars in the cool red supergiant phase, (ii) experience high proper motion into a hot local interstellar medium (ISM), which (iii) produce the formation of a stellar wind bow shock nebula. We present 3D MHD numerical simulations of the astrosphere of the runaway red supergiant IRC −10414, which smooth appearance of its circumstellar bow shock might caused by the ionization of its wind by external sources of radiation. We investigate therein the additional effects of the ISM magnetization and explore how the inclination angle of an ordered background magnetic field with respect to the direction of motion of the red supergiant affects the development of their surroundings. Although our numerical simulations of the bow shock generated by IRC −10414 (the first-ever RSG with an optically detected bow shock) qualitatively reproduce the overall shape and surface brightness of the observed bow shock, they reveal that his internal structure is deeply affected by the direction of the ISM magnetic field, while the stellar magnetic field plays very little role in its shaping. Radiative transfer calculations at optical Ha and NII emission lines also show that the bow shock emission comes mainly from the shocked stellar wind. This naturally explains the enhanced nitrogen abundance in the line-emitting material, derived from the spectroscopy of the astrosphere of IRC-10414.