4 research outputs found
Mass Loss From Planetary Nebulae in Elliptical Galaxies
Early-type galaxies possess a dilute hot (2-10E6 K) gas that is probably the
thermalized ejecta of the mass loss from evolving stars. We investigate the
processes by which the mass loss from orbiting stars interacts with the
stationary hot gas for the case of the mass ejected in a planetary nebula
event. Numerical hydrodynamic simulations show that at first, the ejecta
expands nearly symmetrically, with an upstream bow shock in the hot ambient
gas. At later times, the flow past the ejecta creates fluid instabilities that
cause about half of the ejecta to separate and the other half to flow more
slowly downstream in a narrow wake. When radiative cooling is included, most of
the material in the wake (>80%) remains below 1E5 K while the separated ejecta
is hotter (1E5-1E6 K). The separated ejecta is still less than one-quarter the
temperature of the ambient medium and the only way it will reach the
temperature of the ambient medium is through turbulent mixing (after the
material has left the grid). These calculations suggest that a significant
fraction of the planetary nebula ejecta may not become part of the hot ambient
material. This is in contrast to our previous calculations for continuous mass
loss from giant stars in which most of the mass loss became hot gas. We
speculate that detectable OVI emission may be produced, but more sophisticated
calculations will be required to determine the emission spectrum and to better
define the fraction of cooled material.Comment: 34 pages with 20 figures. Higher quality figures are in the ApJ
versio
Mass Loss From Evolved Stars in Elliptical Galaxies
Most of the X-ray emitting gas in early-type galaxies probably originates
from red giant mass loss and here we model the interaction between this stellar
mass loss and the hot ambient medium. Using two-dimensional hydrodynamic
simulations, we adopt a temperature for the ambient medium of 3E6 K along with
a range of ambient densities and stellar velocities. When the stellar velocity
is supersonic relative to the ambient medium, a bow shock occurs, along with a
shock driven into the stellar ejecta, which heats only a fraction of the gas.
Behind the bow shock, a cool wake develops but the fast flow of the hot medium
causes Kelvin-Helmholtz instabilities to grow and these fingers are shocked and
heated (without radiative cooling). Along with the mixing of this wake material
with the hot medium, most of the stellar ejecta is heated to approximately the
temperature of the hot ambient medium within 2 pc of the star. With the
addition of radiative cooling, some wake material remains cool (< 1E5 K),
accounting for up to 25% of the stellar mass loss. Less cooled gas survives
when the ambient density is lower or when the stellar velocity is higher than
in our reference case. These results suggest that some cooled gas should be
present in the inner part of early-type galaxies that have a hot ambient
medium. These calculations may explain the observed distributed optical
emission line gas as well as the presence of dust in early-type galaxies.Comment: 57 pages, which includes 27 figures; ApJ, in press. A version with
full-resolution figures can be found at
http://www.astro.lsa.umich.edu/~jbregman/public/ms.ps.g