Speaker
Jonathan Mackey
(AIfA, Uni. Bonn)
Description
At least 25 per cent of massive stars are ejected from their parent cluster, becoming runaways or exiles, travelling with often-supersonic space velocities through the interstellar medium (ISM). Their H II regions can strongly impact the structure of the ISM: the overpressurised H II region imparts kinetic energy and momentum to the ISM; it compresses and/or evaporates dense clouds; and it can be used as a diagnostic of the properties of both the star and the ISM. Here we present the first three-dimensional simulations of the H II region around a massive star moving supersonically through a uniform, magnetised ISM, with properties appropriate for the nearby O star Zeta Oph. The H II region leaves an expanding overdense shell behind the star and, inside this, an underdense wake that should be filled with hot gas from the shocked stellar wind. The gas column density in the overdense shell is strongly influenced by the ISM magnetic field strength and orientation because shocks are weak and magnetic pressure is significant. Ionisation front stability is also affected by magnetic field orientation.
For our model parameters, the kinetic energy feedback from the H II region is comparable to the mechanical luminosity of the stellar wind, and the momentum feedback rate is more than 100 times larger than that from the wind and about 10 times larger than the total momentum input rate available from radiation pressure. Compared to the star's eventual supernova explosion, the kinetic energy feedback from the H II region over the star's main sequence lifetime is more than 100 times less, but the momentum feedback is up to 4 times larger. Simulated observations in H-alpha and 21cm neutral H lines are also presented and compared to observations.
Author
Jonathan Mackey
(AIfA, Uni. Bonn)