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Durham e-Theses
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Studies of the physics and chemistry occurring in shock waves associated with regions of star formation

MccCoey, Carolyn (2004) Studies of the physics and chemistry occurring in shock waves associated with regions of star formation. Doctoral thesis, Durham University.



Herbig-Haro (HH) objects, which are observed in molecular, ionic and atomic line emission, are shocked regions within outflows associated with low mass star formation. A 1-D, planar shock code, MHD_VODE, which incorporates an extensive chemistry and calculates the population distributions of various important species throughout the shock wave, is used to model the H(_2) , [Fe II and [C I] line intensities observed from 14 HH objects. It is found that models of non-equilibrium J-type shocks with magnetic precursors are required to reproduce the observed H(_2) emission. These models have shock velocities in the range of 30-50 km s(^-) pre-shock densities of typically 10(^4) cm(^-3) and ages of the order of a few hundred years. However, such models predict a low electron density and are not able to reproduce the observed [Fe I I ] and [C I] emission. The ionization of H following dissociation of H (_2) in a J-type shock results in weak H(_2) emission but can produce the ionization fraction required for the atomic and ionic forbidden line emission. Thus, an elementary representation of a bow shock, consisting of a J-type shock with a magnetic precursor and a J-type shock, respectively, proves successful in reproducing both the H(_2) and Fe I I ] emission. I t is necessary to assume that Fe has previously been eroded from dust grains, probably by the earlier passage of a C-type shock wave. These findings are consistent with observations, which have suggested that HH outflows are episodic phenomena and that the emission from HH objects arises in bow shocks.

Item Type:Thesis (Doctoral)
Award:Doctor of Philosophy
Thesis Date:2004
Copyright:Copyright of this thesis is held by the author
Deposited On:09 Sep 2011 10:02

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