Emission-line strengths and the chemical composition of quasi-stellar objects.

Estimates of emission-line strengths in 160 QSOs are listed. They are used, together with those for 60 objects published earlier, to compile a table of rest-frame equivalent widths for a composite QSO containing 28 lines seen in objects with z from 0.06 to 3.53. Models are computed for matter partially filling a spherical volume, ionized by ultraviolet flux from a central object and optically thick with absorption from heavy elements taken into account. Constant temperature and density are taken for the He II region, where most of the important lines are emitted. Allowance is made for lower and higher temperatures in the H I and He III regions. Emergent emission-line equivalent widths are computed and compared with the observations. An abnormally low helium abundance is not needed to achieve a fit, since the only anomalously weak line is He II 4686 A whose upper level may be depopulated by stimulated emission of He II 1215 A caused by very strong L-alpha 1216 A flux.