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Abstract: Early-type galaxies possess a dilute hot 2-10E6 K gas that is probably thethermalized ejecta of the mass loss from evolving stars. We investigate theprocesses by which the mass loss from orbiting stars interacts with thestationary hot gas for the case of the mass ejected in a planetary nebulaevent. Numerical hydrodynamic simulations show that at first, the ejectaexpands nearly symmetrically, with an upstream bow shock in the hot ambientgas. At later times, the flow past the ejecta creates fluid instabilities thatcause about half of the ejecta to separate and the other half to flow moreslowly downstream in a narrow wake. When radiative cooling is included, most ofthe material in the wake >80% remains below 1E5 K while the separated ejectais hotter 1E5-1E6 K. The separated ejecta is still less than one-quarter thetemperature of the ambient medium and the only way it will reach thetemperature of the ambient medium is through turbulent mixing after thematerial has left the grid. These calculations suggest that a significantfraction of the planetary nebula ejecta may not become part of the hot ambientmaterial. This is in contrast to our previous calculations for continuous massloss from giant stars in which most of the mass loss became hot gas. Wespeculate that detectable OVI emission may be produced, but more sophisticatedcalculations will be required to determine the emission spectrum and to betterdefine the fraction of cooled material.

Autor: Joel N. Bregman, Joel R. Parriott


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