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Astron. Astrophys. 341, 740-750 (1999)

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Complex variability pattern in NGC 4151

II. Variable absorption features

S.G. Sergeev 1,2, V.I. Pronik 1,2, E.A. Sergeeva 1,2 and Yu.F. Malkov 1

1 Crimean Astrophysical Observatory, P/O Nauchny, 334413 Crimea, Ukraine
2 Isaac Newton Institute of Chile, Crimean Branch

Received 17 July 1998 / Accepted 14 October 1998

Abstract

We found and identified the blueshifted variable absorption features in the NGC 4151 optical spectra obtained in 1992-1996. Two of these features identified with He i [FORMULA]4471 and [FORMULA]7065 lines have been investigated in detail. The most striking change in the He i [FORMULA]4471 equivalent width was its strengthening between [FORMULA]JD2450212-JD2450315. We present some indications of the extremely low-ionization state of absorber in this period of observations. We do not find clear evidence for a correlation (neither inverse nor direct) of equivalent widths with the state of the nucleus activity. This probably means that strong changes in the covering factor (or something else) affect this correlation. The decomposition method based on the different behavior of broad emission lines and absorption lines allows us to separate these spectral features, and to obtain evidence that the H[FORMULA], H[FORMULA] and H[FORMULA] absorption lines are also present. The presence of the absorption lines cause the variations of the broad emission profiles to become more complicated. Possible explanations for the absorption variability are discussed.

Key words: galaxies: Seyfert – galaxies: quasars: emission lines – galaxies: quasars: absorption lines – galaxies: nuclei – galaxies: individual: NGC 4151 – galaxies: active

Send offprint requests to: S.G. Sergeev (sergeev@crao.crimea.ua)

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© European Southern Observatory (ESO) 1999

Online publication: December 16, 1998
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