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Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy, 2010.
Heterogeneous processes exist on a variety of astrophysical scales—from galaxies, to
star-forming regions, to stars themselves. Such heterogeneous (clumpy) processes are
a rich area of investigation. The Hubble Space Telescope (HST) has opened up a
window to, for example, the small-scale heterogeneity of jet-like Herbig-Haro (HH)
objects. Complementing this, the vast improvements of computing capability over the
past several decades have allowed theory-driven direct numerical simulation to thrive.
The present work is the result of several sets of simulations—employing adaptive mesh
refinement (AMR) with the AstroBEAR code—seeking to address questions related to
clumpy astrophysical jets. While their morphology typically is ascribed to a periodic or
otherwise smoothly-time-varying launching engine, two alternatives are proposed. The
first examines the role of heterogeneity in the jets’ environment. Several important
correspondences between the simulations and observations are found. Conversely, a
model is proposed in which the jets themselves are heterogeneous. Via a study of
parameter space based on the degree of “clumpiness,” agreement with observations is
found, primarily in morphological and kinematic signatures. Finally, the “clumpy jet”
model brings to light questions concerning the clumps themselves. Specifically, how
the concept of sufficient resolution needs to be modified when the additional physical
process of radiative cooling is included. Radiative cooling removes energy from these
systems primarily from shock-heated gas. Since many observations derive from the same
shock-heating mechanisms, correct modelling when radiative cooling is included is very
important. This question is addressed with a suite of simulations which cover several
decades in resolution. Finally, a new criterion is proposed to take into account the role
of radiative cooling when AMR is employed.
