The Dynamics of Mass-Transferring Binary Star Systems
[1998 - 1999]
In a separate summary report
we have described a published study of the
stability of close, equal-mass binary star systems that
exhibit different degrees of gas compressibility.
Here we briefly describe a related ongoing investigation into
the stability of close binary systems in which the stars have
unequal masses. This is a much more difficult problem in several
respects. First, it is more difficult to construct initial equilibrium
models of unequal-mass binary star systems; second, there is more demand
on the computational tools when simulating the dynamical evolution of
such systems; and third, the variety of systems that can be studied
(i.e., the size of the initial parameter space)
is much much larger. Most importantly, perhaps, is the realization
that when the masses of the two stars are unequal, one star is likely to
fill its Roche lobe before the other and thereby instigate a mass-transfer
event. This, of course, also makes the study of such systems more
interesting in an astrophysical context.
The animation sequence labeled here as "Stable System" demonstrates how
well we are able to follow the orbital motion of an unequal-mass
(mass ratio = 0.81) system in which the less
massive component very nearly fills its Roche lobe. In this movie the
system is being viewed "face-on," and from the inertial frame of reference.
We have followed the dynamical evolution of the system through more than
four full orbits, fully resolving the structure of both polytropic stars.
The two animation sequences shown here to the left depict the very
of evolution in our first test run of an n = 3/2 polytropic system that was
expected to be unstable toward mild mass transfer. The illustrated
system has a mass ratio q = 0.88, and at the beginning of the simulation
the less massive component (shown on the right) is just marginally filling
its Roche lobe. In both movies the system is viewed face-on and from a frame
of reference that is rotating with the orbital frequency of the system.
The "Equatorial Slice" movie displays density contours in the
equatorial plane, highlighting the flow of even the very lowest density
material; the "3D Closeup" movie provides a magnified 3D rendering
of isodensity surfaces in the accretion stream.
Joel E. Tohline
John E. Cazes
Howard S. Cohl
Patrick M. Motl
Patrick M. Motl
This work has been supported, in part, by the U.S. National Science
Foundation through grant
by NASA through ATP grant NAG5-3082,
and by grants of
high-performance-computing time at the
San Diego Supercomputer Center
and through the
of the NAVOCEANO DoD Major Shared Resource Center in Stennis, MS.