Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.662800
Title: Shocked molecular hydrogen in the Orion "bullets"
Author: Tedds, J. A.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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Abstract:
The physics of shocked outflows in molecular clouds is one of the fundamental astrophysical processes by which the cycle of star formation in our Galaxy is regulated. I outline the basis of our understanding of the star formation process and the violent outflow always associated with it, the physics of shocks in molecular gas, and the consequent excitation of molecular hydrogen (H2). It is demonstrated that molecular hydrogen is the best observational diagnostic of this hot, shocked molecular gas and an introduction is given to the observational techniques of near-infrared spectroscopy required in its measurement. I describe a detailed observational study of the physics of shocked H2 excitation and dynamics in the nearby massive star forming region of the Orion giant molecular cloud, the brightest source of its type, using the recently upgraded CGS4 near-IR spectrometer at UKIRT. We have demonstrated that integrated [FeII] 1.644μm line profiles in the Orion "bullets" are consistent with theoretical bow-shock predictions for two different "bullets". We have identified a uniform, broad background component pervading the region in both Fe+ and H2 which is inconsistent with a fluorescent component due to the ionizing radiation of the Trapezium stars alone. A collisionally broadened background component of unidentified origin is measured to be Gaussian in profile with an average FWHM of 26±2.5kms-1 in the H2 1-0 S(1) line after deconvolution of the instrument profile and a peak velocity of 2.5±0.5kms-1, close to the local ambient rest velocity. Crucially, the extended H2 "bullet" wakes have allowed us to dissect individual molecular bow shock structures but the broad (intrinsic FWHM≤27mks-1), singly-peaked H2 1-0 S(1) profiles observed in the two most clearly resolved, plane-of-sky oriented wakes challenge our present understanding. It is very difficult to reconcile any steady-state molecular bow shock model with these observations in Orion. To fit a single C shock absorber model to individual H2 profiles implies a magnetic field strength far in excess of observed estimates and is not consistent with the bow-shaped wake morphology.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.662800  DOI: Not available
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