Numerical Studies of Ablative Mass Loss from Wind Accelerated Clouds.

Details Numerical Studies of Ablative Mass Loss from Wind Accelerated Clouds. Numerical Studies of Ablative Mass Loss from Wind Accelerated Clouds.

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........58k&link_type=abstract

Thesis (PH.D.)--THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL, 1993.Source: Dissertation Abstracts International, Volume: 54

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We have used numerical hydrodynamics to study the acceleration of dense gas clouds via wind ram pressure. Our goal has been to examine a model for the explanation of broad absorption lines (BALs) seen in the spectra of a certain fraction of observed QSOs. This model postulates cool dense clouds moving at very high speeds as the source of the BALs. Furthermore, it invokes simple wind ram pressure as the acceleration mechanism for the clouds. A crucial question is whether the clouds can survive potentially disruptive fluid instabilities, allowing time for acceleration to speeds comparable to the wind velocity. Linear stability arguments imply Rayleigh-Taylor (RT) instability growth occurs on time scales much shorter than the acceleration time scale. These arguments conclude acceleration via ram pressure cannot produce bulk cloud velocities in excess of the cloud's internal sound speed. Our simulations show this is simply not true. We present two-dimensional slab-symmetric simulations where clouds are accelerated to speeds close to an order of magnitude greater than their internal sound speed. Ablative mass loss by the flow of shocked wind gas around the periphery of the clouds acts to limit the growth of potentially disruptive instabilities. Simulations run at different computational grid resolutions clearly show the stabilizing effect ablation has on the evolution of the clouds. Simplified models for line profiles have been developed using mass-velocity histograms generated from the numerical simulations. There is good qualitative agreement between the simulated line profiles and observed BAL profiles.

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