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Session 15 - Structure and Collapse of Molecular Clouds: Theory.
Display session, Monday, January 13
Metropolitan Ballroom,

[15.04] Testing Logatropic Behavior of Turbulent Pressure

E. Vazquez-Semadeni, J. Canto, S. Lizano (Instituto de Astronomia, UNAM)

We present two-dimensional numerical simulations of an isothermal turbulent gas undergoing gravitational collapse, aimed at testing for the presence of ``logatropic'' behavior, as indicated by the evolution of the turbulent velocity dispersion as the density increases during the collapse. A logatropic behavior would require that \Delta v \propto \rho^-1/2, which, however, is not verified in the simulations. Instead, the velocity dispersion increases with the density, in a process reminiscent of the temperature increase upon compression of an ideal gas, although in the present case the change in the ``internal energy'' of the turbulent gas is due to an increase of both the density and the speed of the fluid parcels. We thus suggest that the logatropic ``equation of state'' represents only the statistically most probable state of an ensemble of virialized clouds, but does not adequately represent the behavior of the ``turbulent pressure'' within a single cloud undergoing a thermodynamic process.

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