  We present CO(1-0) and CO(2-1) maps of the LINER galaxy NGC7217, obtained
with the IRAM interferometer, at 2.4"x1.9" and 1.2"x0.8" resolution
respectively. The nuclear ring (at r=12"=0.8kpc) dominates the CO maps, and has
a remarkable sharp surface density gradient at its inner edge. The latter is
the site of the stellar/Halpha ring, while the CO emission ring extends farther
or is broader (500-600pc). This means that the star formation has been more
intense toward the inner edge of the CO ring, in a thin layer, just at the
location of the high gas density gradient. In the CO(2-1) map, a central
concentration inside 3" coincides with a spiral dust lane, clearly seen in the
HST V-I color image. N-body simulations including gas dissipation and star
formation are performed to better understand the nature of the nuclear ring
observed. In the best model, the gas content was higher in the recent past
(having been consumed via star formation), and the oval/spiral formed were more
self-gravitating (abridged).
