Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994hst..prop.5455t&link_type=abstract
HST Proposal ID #5455
Other
Hst Proposal Id #5455 Quasars &Amp, Agn Quasar Absorption
Scientific paper
About 10% of all radio quiet QSOs exhibit broad absorption lines (BALs) in their spectra. The BALs come from a mostly highly ionized region outflowing from the central source at speeds up to many tens of thousands of km/s. Observational constraints on models require that the covering factor of the BAL region be small (e.g., normally < 0.2), therefore many QSOs must have BAL regions which do not lie along our lines-of-sight. For assumptions which should reasonably apply to BAL regions, accurate (algorithm independent) ionic column densities can be derived as a function of outflow velocity for BAL gas. This is unlike the case for broad emission lines in QSOs, which at any observed velocity originates in various components with a range of ionizations. Based on column density analyses, evidence suggests that the chemical composition of the BAL region gas is enhanced by factors of 10 to 100 or more times solar values. Since this conclusion is remarkable, we propose to carefully checked it. One possible problem is that our assumptions about the ability of BAL gas to cover the central source are not universally correct. Another problem with past analyses is that different ionic species of the same element in an object have not been studied. We will remedy these problems by observing the UV spectrum of three specially selected BAL QSOs which currently show the best evidence for enhanced abundances. Constraints on the ionization and chemical composition of the BAL region gas will be derived using Ferland's photoionization code.
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