[Previous] | [Session 110] | [Next]
S.B. Kraemer, D.M. Crenshaw (CUA/GSFC), J.B. Hutchings (DAO), I.M. George (UMBC/GSFC), A.C. Danks (Raytheon/GSFC), T.R. Gull (GSFC), M.E. Kaiser (JHU), C.H. Nelson, D. Weistrop (UNLV)
We have examined the physical conditions in intrinsic UV-absorbing gas in the Seyfert galaxy NGC 4151, using echelle spectra obtained with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) on 1999 July 19. The UV continuum of NGC 4151 was a factor of about 4 lower than in observations taken over the previous two years, and we argue the changes in the column density of the low ionization absorption lines associated with the broad component at -490 km s-1 reflect the decrease in the ionizing flux. We have been able to constrain the densities for this kinematic component and several others based on the strength of absorption lines from metastable states of C~III and Fe~II, and/or the ratios of ground and fine structure lines of O~I, C~II, and Si~II. We have generated a set of photoionization models which not only successfully match the ionic column densities during the present low flux state for each component, but also those seen in previous high flux states with the GHRS and STIS, confirming that the absorbers are photoionized and respond to the changes in the continuum flux. Based on the model parameters (ionization parameter and density), we have been able to map the relative radial positions of the absorbers. Finally, we found that none of the UV absorbers is of sufficiently large column density or high enough ionization state to account for the observed X-ray absorption.
The author(s) of this abstract have provided an email address for comments about the abstract: stiskraemer@yancey.gsfc.nasa.gov