Paul M. Ricker, Ronald E. Taam
The hydrodynamic evolution of the common envelope phase of a low mass binary
composed of a 1.05 Msun red giant and a 0.6 Msun companion has been followed
for five orbits of the system using a high resolution method in three spatial
dimensions. During the rapid inspiral phase, the interaction of the companion
with the red giant's extended atmosphere causes about 25% of the common
envelope to be ejected from the system, with mass continuing to be lost at the
end of the simulation at a rate ~ 2 Msun/yr. In the process the resulting loss
of angular momentum and energy reduces the orbital separation by a factor of
seven. After this inspiral phase the eccentricity of the orbit rapidly
decreases with time. The gravitational drag dominates hydrodynamic drag at all
times in the evolution, and the commonly-used Bondi-Hoyle-Lyttleton
prescription for estimating the accretion rate onto the companion significantly
overestimates the true rate. On scales comparable to the orbital separation,
the gas flow in the orbital plane in the vicinity of the two cores is subsonic
with the gas nearly corotating with the red giant core and circulating about
the red giant companion. On larger scales, 90% of the outflow is contained
within 30 degrees of the orbital plane, and the spiral shocks in this material
leave an imprint on the density and velocity structure. Of the energy released
by the inspiral of the cores, only about 25% goes toward ejection of the
envelope.
View original:
http://arxiv.org/abs/1107.3889
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