Relative effects of ionizing radiation and winds from O-type stars on the structure and dynamics of HII regions

Citation
Er. Capriotti et Jf. Kozminski, Relative effects of ionizing radiation and winds from O-type stars on the structure and dynamics of HII regions, PUB AST S P, 113(784), 2001, pp. 677-691
Citations number
13
Language
INGLESE
art.tipo
Editorial Material
Categorie Soggetti
Space Sciences
Journal title
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC
ISSN journal
0004-6280 → ACNP
Volume
113
Issue
784
Year of publication
2001
Pages
677 - 691
Database
ISI
SICI code
0004-6280(200106)113:784<677:REOIRA>2.0.ZU;2-9
Abstract
The structure and dynamics of H II regions (and some planetary nebulae) are affected not only by radiative heating via photoionization but also by win ds from the embedded O-type stars. When a fast wind (v greater than or equa l to 10(8) cm s(-1)) turns on, a hot (T >> 10(4) K) bubble heated by the wi nd expands into the warm (T similar or equal to 10(4) K) surrounding nebula which is heated and mechanically driven by photoionization. The bubble and a shell of swept-up, i.e., shocked, nebular gas evolve under the influence of mechanical effects and radiative cooling. Previous calculations of wind effects make no direct comparison of the dyna mical effects of the heating through photoionization. In addition, most pre vious calculations deal with particular combinations of wind strength and i nterstellar gas density. Here, we derive simple scaling laws for sphericall y symmetric, homogeneous model nebulae with uniform density and make direct comparison of wind effects and photoionization effects for much wider rang es of nebular densities, stellar luminosities, and wind strengths than have been considered in previous works. Lifetimes, energies, volumes, and masse s of wind-affected material are compared to similar quantities for nebular material heated and driven by photoionization. For the simple models considered in this study, photoionization dominates a s winds with strengths expected for zero-age O-type stars are of little inf luence in the ultimate overall structure and dynamics of radiation-bounded H II regions, except for the "best case for wind" models featuring nebulae of very high density (rho greater than or similar to 10(-19) g cm(-3), N gr eater than or similar to 10(5)-10(6) cm(-3)). Consequently, even though hea ting by photoionization seems to dominate the evolution of H I regions and the formation of H ii regions surrounding O-type stars, dense molecular clo uds may be more strongly influenced by winds. Winds can also be more influe ntial in the overall structure and dynamics of gas-bounded H ii regions of moderate density if the system is sufficiently optically thin to ionizing r adiation.