The gas dynamics around OB association. II - Dependence on the initial ambient density
G. Tenorio-Tagle, M. Beltrametti, P. Bodenheimer, H. W. Yorke;
AaA, 1982, 112, 104
ABSTRACT:One- and two-dimensional calculations of the gasdynamical evolution of H II regions excited by
an evolving OB association are presented.
The various phases
(classical expansion, recombination, reionization and full recombination,
phases I-IV, respectively) are studied and found to depend not only on the
behaviour of the stellar photon flux, but also on the initial value of the ambient
density.
Phase II, (recombination) leads to the formation of a large expanding thick
neutral shell.
However, for large values of the ambient density, phase II can
be inhibited and the H II region will continue to expand according to the
classical formulation, even though the ionizing photon flux from the source
continues to decay.
The latter evolution will make the H II region appear as a
ring-like nebula for a considerable period of time.
Many of the galactic and
extragalactic ring-like nebulae and expanding neutral shells, usually interpreted
as the result of supernova explosions or stellar winds, can thus be
explained with the present calculations.
KEYWORDS: b stars, gas dynamics, o stars, stellar envelopes, stellar evolution, h ii regions, ionizing radiation, nebulae, star clusters, stellar winds
PERSOKEY:region hii, ,
CODE: tenorio-tagle82