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Title: Evolution of prestellar cores
Author: Simpson, Robert J.
ISNI:       0000 0004 2750 6159
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2010
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In this thesis I re-analyse the SCUBA archive data for the L1688 main cloud of Ophiuchus, incorporating all available scan-map and jiggle-map data. I create a new core mass function (CMF) for L1688 using updated values for the distance to this region, as well as new estimates for the temperatures and masses of the cores. I show that the CMF for LI688 is consistent with a three part power-law, with slopes the same as those seen in the stellar IMF. The deeper maps allows the discovery of a turnover in the CMF at 0.7A/, which shows that the core mass function appears to mimic the stellar initial mass function. This concordance is indicative that the stellar IMF is determined at the prestellar core phase. I also present HCO* (J=4 > 3) spectral line observations from HARP on the JCMT. Data are presented for 59 of the prestellar cores mapped using SCUBA. Using these data. I present a proposed evolutionary diagram for prestellar cores in the form of a radius-mass plot. I hypothesise that a core is formed in the low-mass, low-radius region of the plot. It then accretes quasi-statically, increasing in both mass and radius. When it crosses the limit of gravitational instability it begins to collapse, decreasing in radius, towards the region of the diagram where protostellar cores are seen. My predictions are borne out when I plot the collapsing cores on this diagram. I outline an analytical model, created by Whitworth & Ward-Thompson (2001), describing the collapse of a starless core with a Plummer-like density profile. I describe my addition of a simple radiative transfer code, which allows simulated spectral line profiles to be created for such cores. The model is shown to be consistent with previous models, and with the observed physical properties of prestellar cores. This model is applied to 20 of the spectral line profiles from the HCO+ (J=4 + 3) data. These 20 modelled cores are placed onto the proposed evolutionary diagram. Their modelled physical states are found to be consistent with the proposed evolutionary track. In conjunction with the SCUBA and HARP data, these fits allow a potential timeline for the LI688 cloud to be established for the first time.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available