Long-term variability of the optical spectra of NGC 4151: II. Evolution
  of the broad Ha and Hb emission-line profiles
  Results of the long-term (11 years, from 1996 to 2006) H$\alpha$ and H$\beta$
line variations of the active galactic nucleus of NGC 4151 are presented. High
quality spectra (S/N>50 and R~8A) of H$\alpha$ and H$\beta$ were investigated.
We analyzed line profile variations during monitoring period. Comparing the
line profiles of H$\alpha$ and H$\beta$, we studied different details (bumps,
absorption features) in the line profiles. The variations of the different
H$\alpha$ and H$\beta$ line profile segments have been investigated. Also, we
analyzed the Balmer decrement for whole line and for line segments. We found
that the line profiles were strongly changing during the monitoring period,
showing blue and red asymmetries. This indicates a complex BLR geometry of NGC
4151 with, at least, three kinematically distinct regions: one that contributes
to the blue line wing, one to the line core and one to the red line wing. Such
variation can be caused by an accelerating outflow starting very close to the
black hole, where the red part may come from the region {closer to the black
hole than the blue part, which is coming} from the region having the highest
outflow velocities. Taking into account the fact that the BLR of NGC 4151 has a
complex geometry (probably affected by an outflow) and that a portion of the
broad line emission seems to have not a pure photoionization origin, one can
ask the question whether the study of the BLR by reverberation mapping may be
valid in the case of this galaxy.
