New observations of the optical spectrum of the Seyfert galaxy NGC 4151

Spectra and scans of NGC 4151 are found to show broad lines of He I and Fe II. The He I lines are twice the width of the Balmer line wings and the broad line spectrum closely resembles that of 3C 273. Limits to the density and temperature for the region emitting the broad lines are deduced. The narrow forbidden lines are emitted in a region with log T = 4.07 +-0.03 and density (possibly stratified) between log Nsub(e) approximately 4.3 and 3.7. How the hydrogen and helium line widths can differ is briefly discussed. Possible reasons for the difference between quasars and Seyferts with Fe II emission and those with strong forbidden line spectra are advanced. (author)