Computer Science
Scientific paper
Jul 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984iue..prop.1753a&link_type=abstract
IUE Proposal ID #NPFHW
Computer Science
Scientific paper
Recent far infrared and radio observations have revealed the presence of massive dense neutral atomic and molecular components in the shells of young planetary nebulae and their supposed progenitors. The total mass contained in these components appears to exceed that of the ionized component of planetary nebulae by an order of magnitude, therefore constituting the majority of the mass shed during the evolution of the central star. The chemistry of this shell can be described as photochemical alteration of a pre-existing circumstellar molecular shell. The composition of such a shell can be expected to favor neutral and singly ionized heavy atoms, copious amounts of molecular hydrogen, and some heavy molecules. The UV resonance lines of C I have been detected in absorption against the central stars in several planetaries and constitute a singularly powerful probe of the ionization, temperature and density structure in the shell. We propose to investigate these multiplets at high resolution to decipher their velocity structure, and to determine line of sight C I column densities for comparison to far infrared and radio observations. If the density were high enough, absorption arising from the finestructure levels of the C I multiplets might also be seen. The relative populations of the fine-structure levels constrains the density and temperature within the neutral shells surrounding planetaries. The results of this study will clarify the interpretation of these latter lines, and sharpen our understanding of chemical processes in circumstellar shells.
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