Evolution of the accretion disk in the nucleus of NGC 1097

Abstract

We discuss the long-term evolution of the broad double-peaked H alpha profile of the LINER/Seyfert 1 nucleus of NGC 1097. Besides the previously known variation of the relative intensities of the blue and red peaks, the profile has recently shown an increasing separation between the two peaks, at the same time as the integrated flux has decreased. We successfully model these variations using a precessing asymmetric accretion disk with a varying emissivity law. We interpret the emissivity variation as due to the fact that the source of ionization is getting dimmer, causing the region of maximum emission to drift inwards (and thus to regions of higher velocities). In addition, in the last 3 yrs of observations, the central wavelength of the double-peaked line has shifted to bluer wavelengths, which may be due to a wind from the disk. It is the first time that such evolution is observed so clearly, giving additional support for an accretion disk as the origin of the double-peaked profile in NGC 1097.