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Evolutionary Models of the Dissociation Zones Surrounding HII Regions

Published online by Cambridge University Press:  04 August 2017

R. S. Roger
Affiliation:
Dominion Radio Astrophysical Observatory, Herzberg Institute of Astrophysics, Penticton, B.C., Canada
P. E. Dewdney
Affiliation:
Dominion Radio Astrophysical Observatory, Herzberg Institute of Astrophysics, Penticton, B.C., Canada

Extract

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Atomic hydrogen regions have been observed in λ21-cm emission around a number of galactic HII regions in various stages of evolution (Roger & Pedlar, 1981; Dewdney & Roger, 1982; Roger & Irwin, 1982). These HI zones are almost certainly formed by the dissociation of H2 with Lyman-Werner band photons in the UV from the exciting stars. We describe some results of the computer modelling of the advancement of dissociation fronts with time as functions of various parameters, principally stellar type and ambient gas density. The modelling has shown that for most conditions a substantial HI zone is formed fairly rapidly around a new star. When the dissociation front moves out to a distance where absorbing molecules are predominantly in the ground vibrational state, further advancement of the front is much slower.

Type
I. Star Forming Processes in the Solar Neighborhood
Copyright
Copyright © Reidel 1987 

References

Dewdney, P.E. and Roger, R.S. 1982, Ap. J. 255, 564 Google Scholar
Roger, R.S. and Irwin, J.A. 1982, Ap. J. 256, 127 Google Scholar
Roger, R.S. and Pedlar, A. 1981, Astron. Astrophys. 94, 238 Google Scholar
Stecher, T.P. and Williams, D.A. 1967, Ap. J. Lett. 149, L29 Google Scholar