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Two Dimensional Models for the Orion Nebula and M17

Published online by Cambridge University Press:  04 August 2017

R. H. Rubin
Affiliation:
NASA, Ames Research Center, Moffett Field, CA 94035. USA
J. P. Simpson
Affiliation:
NASA, Ames Research Center, Moffett Field, CA 94035. USA
E. F. Erickson
Affiliation:
NASA, Ames Research Center, Moffett Field, CA 94035. USA
M. R. Haas
Affiliation:
NASA, Ames Research Center, Moffett Field, CA 94035. USA

Extract

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We apply a 2-D, axisymmetric code for modeling H II regions (Rubin Ap. J. 287, 653, 1984) to observations of the Orion Nebula. The model solves for the ionization and thermal structure and radiative transfer for the quasi-equilibrium volume. Assuming that the Orion Nebula is viewed face-on (along the symmetry axis) and that the geometry/density distribution is plane parallel with an exponential density gradient perpendicular to the slab, we use a x2 minimization technique to best fit the radio continuum maps. The best fit to the Schraml and Mezger map (Astrophys. J. 156, 269, 1969) has a density at the star of ∼1800 cm−3, a scale height of ∼0.23 pc, and ∼1.5x1049 ionizing photons s−1 so that ∼ 1/3 of the ionizing photons from the exciting source are escaping the nebula through the frontal density-bounded direction. Our model for Orion requires circular symmetry in the plane of the sky; nonsymmetrical features such as the ionization bar toward the SE cannot be reproduced. Further modeling that compares with line observations has been delayed to incorporate the important role played by recombinations in populating low-lying [O II] levels (Rubin 1985, Astrophys. J., submitted).

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