Computer Science
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992hst..prop.3660t&link_type=abstract
HST Proposal ID #3660
Computer Science
Hst Proposal Id #3660
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 which is outflowing from the central source at speeds ranging from a few to many tens of thousands of km/s. Observational constraints on models require that the covering factor of the BAL region be relatively small (e.g., normally < 0.2), therefore many QSOs must have BAL regions which do not lie along our lines- of-sight. Fairly accurate ionic column densities can be derived as a function of velocity for BAL gas. This is unlike the case for broad emission from QSOs, which at any observed velocity originates in various components with a range of ionizations. Based on column density analyses, a considerable amount of 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 check it. One problem with past analyses is that different ionic species of the same element in an object have not been studied. We will remedy this situation by observing the UV spectrum of this specially selected BAL QSO which shows evidence for enhanced abundance and whose BAL profile is simple enough to reduce complications due to overlapping of the absorption due to different species. Constraints on the ionization state and chemical composition of the BAL gas will be derived using Ferland's photoionization code CLOUDY.
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