Andreas H. W. Kuepper, Richard R. Lane, Douglas C. Heggie
We investigate the epicyclic motion of stars escaping from star clusters.
Using streaklines, we visualise the path of escaping stars and show how
epicyclic motion leads to over- and underdensities in tidal tails of star
clusters moving on circular and eccentric orbits about a galaxy. Additionally,
we investigate the effect of the cluster mass on the tidal tails, by showing
that their structure is better matched when the perturbing effect of the
cluster mass is included. By adjusting streaklines to results of N-body
computations we can accurately and quickly reproduce all observed substructure,
especially the streaky features often found in simulations which may be
interpreted in observations as multiple tidal tails. Hence, we can rule out
tidal shocks as the origin of such substructures. Finally, from the adjusted
streakline parameters we can verify that for the star clusters we studied
escape mainly happens from the tidal radius of the cluster, given by x_L =
(GM/(\Omega^2-\partial^2\Phi/\partial R^2))^{1/3}. We find, however, that there
is another limiting radius, the "edge" radius, which gives the smallest radius
from which a star can escape during one cluster orbit about the galaxy. For
eccentric cluster orbits the edge radius shrinks with increasing orbital
eccentricity (for fixed apocentric distance) but is always significantly larger
than the respective perigalactic tidal radius. In fact, the edge radii of the
clusters we investigated, which are extended and tidally filling, agree well
with their (fitted) King radii, which may indicate a fundamental connection
between these two quantities.
View original:
http://arxiv.org/abs/1111.5013
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