  We study the evolution of the broad, double-peaked Halpha emission-line
profile of the LINER/Seyfert 1 nucleus of NGC 1097, using 24 spectra obtained
over a time span of 11 yrs - from 1991 Nov. through 2002 Oct. While in the
first 5 yrs the main variation was in the relative intensity of the blue and
red peaks, in the last years we have also observed an increasing separation
between the two peaks, at the same time as the integrated flux in the broad
line has decreased. We propose a scenario in which the emission originates in
an asymmetric accretion disk around a supermassive black hole, whose source of
ionization is getting dimmer, causing the region of maximum emission to come
closer to the center (and thus to regions of higher projected velocity). We use
the observations to constrain the evolution of the accretion disk emission and
to evaluate two models: the elliptical disk model previously found to reproduce
the observations from 1991 to 1996 and a model of a circular disk with a single
spiral arm. We favor the latter, because the whole set of data is consistent
with a monotonic precession of the spiral pattern, which has completed almost
two revolutions since 1991. The precession period implies a black hole mass of
approximately 5x10^7 solar masses. Finally, we have found tentative evidence of
the emergence of an accretion disk wind, which we hope to explore further with
future observations.
