Monte Carlo models of the physical and chemical properties of inhomogeneous interstellar clouds.

Details Monte Carlo models of the physical and chemical properties of inhomogeneous interstellar clouds. Monte Carlo models of the physical and chemical properties of inhomogeneous interstellar clouds.

Mar 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...307..271s&link_type=abstract

Astronomy and Astrophysics, v.307, p.271

Astronomy and Astrophysics

Astrophysics

87

Ism: Clouds, Structure, Molecules, Atoms

Scientific paper

Two-dimensional model calculations for inhomogeneous interstellar clouds are presented. These models can accommodate an arbitrary geometry and density structure. The equation for radiative transfer in the continuum is solved by means of a Monte Carlo method. Self-shielding of H_2_ and CO, as well as the shielding of CO by H_2_, is treated in the one-line approximation. The detailed temperature structure of the model cloud is calculated taking all the relevant heating and cooling processes into account. Models are presented for diffuse and translucent clouds with A_V_=1-5mag. The inhomogeneous nature of interstellar clouds influences the abundances and excitation of atomic and molecular species. Specifically, it is shown that C^+^ is found mostly in the interclump medium, whereas ^13^CO traces mainly the dense clumps. Atomic carbon, C, has its largest abundance in the surface layers of the clumps. The calculated column densities for inhomogeneous and homogeneous models are compared, and it is shown that the inhomogeneous models lead to a large increase (up to a factor of 5) in the CO column density but to a decrease in the abundances of species that do not shield themselves against photodissociation. The inhomogeneous structure also affects the temperature structure, resulting in enhanced temperatures deeper into the cloud. The contribution of small grains and large molecules like Polycyclic Aromatic Hydrocarbons (PAHs) is significant at the edge of the cloud. The observational consequences for the [CII] 158 μm and [CI] 609 μm line maps are discussed.

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