6
Morphology
of
Massiv
e
Stars
and
Ionized
Gas
This chapter presents direct observational evidence supporting popular mod-
els that predict the interaction between sites of massive star formation and the
ISM. The relationship between the massive stellar component and the ionized
component is examined via comparisons of FUV and H observations providing a
window to view the e ects of massive star formation on the surrounding gaseous
medium. These comparisons emphasize the identi cation of processes acting on
local scales, the rst step in understanding star formation triggering mechanisms.
6.1 Evolution of Young Star Formation Regions
Once star formation commences, stars begin dumping energy into their sur-
rounding ISM via ionizing photons, supernovae explosions, stellar winds, and out-
ows. Combined, these processes have a profound a ect on the surrounding region
of gas. The ionizing photon bath alone, provided by UV photons from massive
stars, can deposit prodigious amounts of kinetic energy into the ISM. For exam-
ple, a single massive star provides roughly 10
50
ergs of kinetic energy as fast mov-
ing ionized gas. The champagne" model Tenorio-Tagle 1979, summarized by
Hunter 1992, describes the process by which massive stars ionize their surround-
ing gas creating compact HII regions that evolve into extended objects. Starting
as a ultracompact HII region, the exciting star and surrounding ionized cloud, lies
deep within the dense molecular cloud in which it formed. The ionization front of
74
