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Title: Simulations of star formation in Ophiuchus
Author: Lomax, Oliver David
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2013
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The way in which stars form from the interstellar medium is poorly understood. In this thesis we investiage the process star formation in molecular clouds via core fragmentation using Smoothed Particle Hydrodynamics (SPH). The initial conditions of the simulations are informed as closely as possible by observations of Ophiuchus. We run large ensebles of individual core simulations and compare the collective results with observations of stars and brown dwarfs. We use observations of Ophiuchus by Motte et al. (1998) and Andre et al. (2007) to calibrate a lognormal distribution from which we draw correlated masses, sizes and velocity dispersions. We assume that the cores are intrinsically triaxial. The distribution of core shapes is then inferred by fitting a single parameter family of ellipsoidal shapes to the observed core aspect ratios. Each core is given the density profile of a critical Bonnor-Ebert sphere and a turbulent velocity field which is modified to include ordered rotation and radial excursions. We evolve one hundred of the model prestellar cores using the Seren SPH code (Hubber et al., 2011). The simulations are repeated with continuous accretion heating, no accretion heating and episodic accretion heating (Stamatellos et al., 2012). We find that simulations with episodic accretion heating can reproduce the general features of the Chabrier (2005) initial mass function. This includs the ratio of stars to brown dwarfs and the turn-over at 0:2M�. We demonstrate that the mass of a star is not related to the mass of the prestellar core in which it formed. Low mass cores with Mcore � 0:1M� tend to collapse into single objects whereas higher mass cores with Mcore & 1M� can fragment into tens of objects. We finally show that the multiplicy statistics of the protostars formed in these simulations are well matched by observations. Multiplicity frequencies are higher than those of field stars and we note the presence of long-lived quadruple, quintuple and sextuple systems.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy