Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

Abstract

At least 5 per cent of the massive stars are moving supersonically through\nthe interstellar medium (ISM) and are expected to produce a stellar wind bow\nshock. We explore how the mass loss and space velocity of massive runaway stars\naffect the morphology of their bow shocks. We run two-dimensional axisymmetric\nhydrodynamical simulations following the evolution of the circumstellar medium\nof these stars in the Galactic plane from the main sequence to the red\nsupergiant phase. We find that thermal conduction is an important process\ngoverning the shape, size and structure of the bow shocks around hot stars, and\nthat they have an optical luminosity mainly produced by forbidden lines, e.g.\n[OIII]. The Ha emission of the bow shocks around hot stars originates from near\ntheir contact discontinuity. The H$\\alpha$ emission of bow shocks around cool\nstars originates from their forward shock, and is too faint to be observed for\nthe bow shocks that we simulate. The emission of optically-thin radiation\nmainly comes from the shocked ISM material. All bow shock models are brighter\nin the infrared, i.e. the infrared is the most appropriate waveband to search\nfor bow shocks. Our study suggests that the infrared emission comes from near\nthe contact discontinuity for bow shocks of hot stars and from the inner region\nof shocked wind for bow shocks around cool stars. We predict that, in the\nGalactic plane, the brightest, i.e. the most easily detectable bow shocks are\nproduced by high-mass stars moving with small space velocities.\n