Massive Stars and the Energy Balance of the Interstellar Medium. I. The Impact of an Isolated 60M⊙Star

We present results of numerical simulations carried out with a 2D radiationhydrodynamics code in order to study the impact of massive stars on theirsurrounding interstellar medium. This first paper deals with the evolution ofthe circumstellar gas around an isolated 60 Msun star. The interaction of thephotoionized HII region with the stellar wind bubble forms a variety ofinteresting structures like shells, clouds, fingers, and spokes. These resultsdemonstrate that complex structures found in HII regions are not necessarilyrelics from the time before the gas became ionized but may result fromdynamical processes during the course of the HII region evolution. We have alsoanalyzed the transfer and deposit of the stellar wind and radiation energy intothe circumstellar medium until the star explodes as a supernova. Although thetotal mechanical wind energy supplied by the star is negligible compared to theaccumulated energy of the Lyman continuum photons, the kinetic energy impartedto the circumstellar gas over the star's lifetime is 4 times higher than for acomparable windless simulation. Furthermore, the thermal energy of warmphotoionized gas is lower by some 55%. Our results document the necessity toconsider both ionizing radiation and stellar winds for an appropriatedescription of the interaction of OB stars with their circumstellarenvironment.Comment: 60 pages, 23 figures, 3 tables, accepted for publication in the Astrophysical Journa