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Scientific paper
Jul 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004hst..prop10124f&link_type=abstract
HST Proposal ID #10124
Other
Hst Proposal Id #10124 Ism
Scientific paper
Star formation is governed by a complex interplay among magnetic, thermal, turbulent and gravitational energies. Of these, magnetic energies are the most difficult to measure. Yet magnetic energies are crucial to the evolution of molecular clouds if they are comparable to other energies. Unfortunately, magnetic field strength measurements are sparse. Moreover, detailed field strength maps exist in only one region of the ISM, the veil of neutral material in front of the Orion Nebula. From the Zeeman effect in 21cm HI absorption lines, we have accurate maps of the line-of-sight field strength in two independent velocity components of the veil. Therefore, the veil presents a unique laboratory for study of magnetic effects in star forming regions. We have recently combined archival UV absorption line data with photoionization models to estimate the veil's density, temperature and level of ionization. On this basis, we infer that magnetic energies far exceed turbulent and thermal energies in at least one HI velocity component. This component is magnetically unique. All other data about star forming regions suggest equipartition between magnetic and turbulent energies. Our analysis of physical conditions in Orion's veil suffers from an important limitation. Existing UV absorption line data have insufficient spectral resolution to separate the two HI velocity components. Therefore, our models reflect average conditions in the two components. Yet actual conditions are likely to be quite different since one component must lie closer to the source of ionization. We propose to use STIS to obtain high resolution UV spectra of Theta 1 Ori B. These data will allow us to model the two velocity components separately. We can then estimate magnetic and other energies in the two components. We will determine if the apparent magnetic uniqueness of one component applies to both, and we will estimate the distances of each component from the ionizing stars. This study will provide the most comprehensive information obtainable about the role of magnetic effects in a star forming region.
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