Balmer and He I absorption in the nuclear spectrum of NGC 4151
  Spectra taken with the Space Telescope Imaging Spectrograph (STIS) allow accurate location and extraction of the nuclear spectrum of NGC 4151, with minimal contamination by extended line emission and circumnuclear starlight. Spectra since 1997 show that the P Cygni Balmer and He I absorption seen previously in low nuclear states, is present in higher states, with outflow velocity that changes with the nuclear flux. The phenomenon is discussed in terms of some of the absorbers seen in the UV resonance lines, and outflows from the central source and surrounding torus. 
J.B. Hutchings (HIA/NRC), D.M. Crenshaw (Georgia State Univ), S.B.   Kraemer, J.R. Gabel (Catholic Univ of America), M.E. Ka...