Balmer and He I Absorption in the Nuclear Spectrum of NGC 4151
Gull, T. R.; Kraemer, S. B.; Crenshaw, D. M.; Hutchings, J. B.; Gabel, J. R.; Kaiser, M. E.; Weistrop, D.
Canada, United States
Abstract
Spectra taken with the Space Telescope Imaging Spectrograph 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 in terms of outflows from the central source and surrounding torus.
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.