Structure of Stationary Photodissociation Fronts
| dc.creator | Draine, B. T. | |
| dc.creator | Bertoldi, Frank | |
| dc.date | 1996-03-08 | |
| dc.date.accessioned | 2026-07-07T11:14:21Z | |
| dc.date.available | 2026-07-07T11:14:21Z | |
| dc.description | The structure of stationary photodissociation fronts is revisited. H_2 self- shielding is discussed, including the effects of line overlap. We find that line overlap is important for N(H_2) > 10^{20} cm^{-2}. We compute multiline UV pumping models, and compare these with simple analytic approximations for the effects of self-shielding. The overall fluorescent efficiency of the photodissociation front is obtained for different ratios of chi/n_H (where chi characterizes the intensity of the incident UV) and different dust extinction laws. The dust optical depth tau_{pdr} to the point where 50% of the H is molecular is found to be a simple function of a dimensionless quantity phi_0 depending on chi/n_H, the rate coefficient for H_2 formation on grains, and the UV dust opacity. The fluorescent efficiency of the PDR also depends primarily on phi_0 for chi<3000 and n_H<10^4 cm^{-3}; for stronger radiation fields and higher densities radiative and collisional depopulation of vibrationally-excited levels interferes with the radiative cascade. The emission spectrum from the PDR is essentially independent of the color temperature $T_{color}$ of the incident UV for T_{color}>10^4K, but shows some sensitivity to the v-J distribution of newly-formed H_2. The 1-0S(1)/2-1S(1) and 2-1S(1)/6-4Q(1) intensity ratios, the ortho/para ratio, and the rotational temperature in the $v$=1 and $v$=2 levels are computed as functions of the temperature and density, for different values of chi and n_H. We apply our models to the reflection nebula NGC 2023. We are best able to reproduce the observations with models having chi=5000, n_H=10^5 cm^{-3}. | |
| dc.description | 50 pages, 24 eps figures, uses aaspp4.sty . To appear in Ap.J | |
| dc.identifier | https://arxiv.org/abs/astro-ph/9603032 | |
| dc.identifier | http://arxiv.org/abs/astro-ph/9603032 | |
| dc.identifier | Astrophys.J.468:269,1996 | |
| dc.identifier | doi:10.1086/177689 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/192041 | |
| dc.subject | Astrophysics | |
| dc.title | Structure of Stationary Photodissociation Fronts | |
| dc.type | text |