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.