The absorption-line spectrum of NGC 4151

Spectroscopic observations of the blueshifted absorption-line spectrum of NGC 4151 are presented. The strengths and profiles of these lines are variable and the variations in strength are correlated with the ultraviolet brightness fluctuations of the nuclear continuum. The lines arise from metastable levels of R I and Re I and the level populations seem to be governed, via photoionization, by the brightness of the variable continuum source. On the basis of the available observational information, it is concluded that the region in which tbese absorption features arise is characterized by fle > 106 cm -3 and is located 0.025 pc from the continuum source. The variations in absorption-line strength are approximately sufficient to account for the observed emission-line variability near Ra. It is also shown that the broad Balmer emission wings must arise in a region interior to that in which the absorption lines are formed. The wing-emission region has n > 10 cm-3 and is optically thick to electron scattering. Subject headings: galaxies, individual - line profiles - Seyfert galaxies