Massive Stars and the Energy Balance of the Interstellar Medium. II. The 35 M ⊙ Star and a Solution to the “Missing Wind Problem”

Abstract

We continue our numerical analysis of the morphological and energeticinfluence of massive stars on their ambient interstellar medium for a 35M_{solar} star that evolves from the main-sequence through redsupergiant and Wolf-Rayet phases, until it ultimately explodes as asupernova. We find that structure formation in the circumstellar gasduring the early main-sequence evolution occurs as in the 60M_{solar} case but is much less pronounced because of the lowermechanical wind luminosity of the star. On the other hand, since theshell-like structure of the H II region is largely preserved, effectsthat rely on this symmetry become more important. At the end of thestellar lifetime 1% of the energy released as Lyman continuum radiationand stellar wind has been transferred to the circumstellar gas. Fromthis fraction 10% is kinetic energy of bulk motion, 36% is thermalenergy, and the remaining 54% is ionization energy of hydrogen. Thesweeping up of the slow red supergiant wind by the fast Wolf-Rayet windproduces remarkable morphological structures and emission signatures,which are compared with existing observations of the Wolf-Rayet bubbleS308, whose central star has probably evolved in a manner very similarto our model star. Our model reproduces the correct order of magnitudeof observed X-ray luminosity, the temperature of the emitting plasma,and the limb brightening of the intensity profile. This is remarkable,because current analytical and numerical models of Wolf-Rayet bubblesfail to consistently explain these features. A key result is that almostthe entire X-ray emission in this stage comes from the shell of redsupergiant wind swept up by the shocked Wolf-Rayet wind rather than fromthe shocked Wolf-Rayet wind itself as hitherto assumed and modeled. Thisoffers a possible solution to what is called the ``missing windproblem'' of Wolf-Rayet bubbles.