AAS 207th Meeting, 8-12 January 2006
Session 195 Kinematics of the ISM
Oral, Thursday, 10:00-11:30am, January 12, 2006, Salon 3

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[195.06] The Ionisation Fraction in Clumpy Molecular Clouds

T.J. Bethell, E.G. Zweibel (University of Wisconsin - Madison)

The interstellar medium is clumpy, a property which is often considered important when attempting to reconcile differences between models and observations. While simple (two-phase, fractal) models have their successes and failures, we now have physically motivated turbulently driven MHD models. These offer perhaps the most realistic models yet of the clumpiness in molecular clouds.

We present results of radiative transfer (using a Reverse Monte Carlo scheme) in turbulent MHD models, and its effects on the abundances of important chemical species in a large time-dependent chemical network.

In the presence of a penetrating radiation field the clumpiness tends to make the mass darker, suppressing photochemistry, while the interclump medium may be brightly illuminated and undergoes markedly different chemistry.

Where appropriate we also solve iteratively for the case where H2 is self-shielding, following the character of the H/H2 reservoir which plays a central role in astrochemistry. Clumping tends to enhance self-shielding, causing the global distribution of hydrogen to become molecular both sooner temporally and at lower AV, when compared with homogeneous models.

Particular attention is paid to the ionisation fraction which may play an important role in magnetic field transport. This work may be extended to the later stages of star formation.

This research is supported by NSF, NASA and the University of Wisconsin NSF grant.

The author(s) of this abstract have provided an email address for comments about the abstract: bethell@astro.wisc.edu

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