Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.649211
Title: The molecular structure of Herbig-Haro objects, outflows and jets from young stellar objects
Author: Davis, C. J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1992
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Abstract:
The observations discussed in this thesis are of regions of star-formation where outflow is believed to be occurring. Specifically, radio, millimeter/sub-millimeter and infrared observations are made to illustrate the molecular structure of outflows and related phenomena. CO J = 2-1 observations of the molecular outflow from the infrared reflection nebulae GGD27 IRS complement earlier CO J&61 1-0 observations and further allow us to revise previous estimates of the outflow mass and energetics. The mass derived here is comparable to mass estimates for other outflows from similarly luminous sources, though it is a factor of ~10 less than that derived from the earlier CO 1-0 observations. This difference is due to the choice of excitation temperature used in deriving the outflow mass; here combining CO 2-1 observations with the 1-0 studies allows us to calculate T_ex more precisely. I also show that the conical outflow overlaps the plain of the sky, and find that the observed molecular flow is not powerful enough to excite the associated HH nebulae HH80/81. Studies of the molecular environment around the HH objects HH1 and 2, and towards the optical jet/HH bow-shock system HH34 reveal the presence of dense, quiescent molecular material associated with all three HH objects. The presence of such stationary, molecular clumps, particularly evident in HH2 and HH34, does not support current popular HH models. Observations of these regions in a number of molecular species also show how contrasting and sometimes misleading observations in different molecular gas tracers can be: In HH2 peaks seen in NH_3 (,1) do not coincide with the well resolved clump observed in HCO^+ J = 3-2, whilst the C^18O J = 2-1 emission shows no clear peak at all. These contrasting morphologies are thought to be due to the differing excitation requirements of the observed lines. However, in HH34 chemical abundance variations are also significant: Towards the exciting source of the optical stellar jet and HH bow-shock, the NH_3 is underabundant. Indeed, in many other outflow sources, a similar NH_3 depletion is observed towards the central source. Instead, the NH_3 delineates a toroidal structure that encircles the central gas-density peak and the outflow source.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.649211  DOI: Not available
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