Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...451..210r&link_type=abstract
Astrophysical Journal v.451, p.210
Astronomy and Astrophysics
Astronomy
19
Hydrodynamics, Ism: Clouds, Line: Formation, Radiative Transfer, Shock Waves
Scientific paper
We solve the line transfer problem in evolving H ii regions in order to calculate line profiles of hydrogen recombination (Hα) and forbidden oxygen ([O III] 5007) lines along several lines of sight during the photo- disruption of molecular cloud cores, or high-density condensation. The density, velocity, and ionization structure of spherically symmetric models with an initial power-law density distribution, ρ ∝ r-w, were used to calculate the source function. We differentiate between two possible evolutions: the classical evolution (w ≤ 1.5), in which upon expansion of the ionized gas a shock is driven into the neutral intercloud medium, and evolution for steeper density gradients (w > 1.5), in which the "champagne" phase develops as the whole cloud becomes ionized by a supersonic R-type ionization front. Thus a strong shock is driven into the ionized gas by the expansion of the denser cloud core. The rapid expansion of these high-density cores generates supersonic outflows as well as important variations in the H II equilibrium temperature, which ranges from 103 K within the core to 8 × 104 K behind the champagne shocks. As a result, the line profiles in these cases may present partial or total splitting both in Hα and in [O III] λ5007. Also the surface brightness distributions of the oxygen line traces mainly the hot (T > 3 × 104 K) and fast-moving shocked gas, and the Hα traces the slower, purely photoionized matter (T 10 K). Thus the continuous and rapid disruption of condensations, driven by the pressure imbalance created by photoionization within a star-forming cloud, adds a supersonic bulk motion to the uniform velocity field expected from the classical evolution.
Franco Jose
Rodriguez-Gaspar J. A.
Tenorio-Tagle Guillermo
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