  The Galactic center hosts several hundred early-type stars, about 20% of
which lie in the so-called clockwise disk, while the remaining 80% do not
belong to any disks. The circumnuclear ring (CNR), a ring of molecular gas that
orbits the supermassive black hole (SMBH) with a radius of 1.5 pc, has been
claimed to induce precession and Kozai-Lidov oscillations onto the orbits of
stars in the innermost parsec. We investigate the perturbations exerted by a
gas ring on a nearly-Keplerian stellar disk orbiting a SMBH by means of
combined direct N-body and smoothed particle hydrodynamics simulations. We
simulate the formation of gas rings through the infall and disruption of a
molecular gas cloud, adopting different inclinations between the infalling gas
cloud and the stellar disk. We find that a CNR-like ring is not efficient in
affecting the stellar disk on a timescale of 3 Myr. In contrast, a gas ring in
the innermost 0.5 pc induces precession of the longitude of the ascending node
Omega, significantly affecting the stellar disk inclination. Furthermore, the
combined effect of two-body relaxation and Omega-precession drives the stellar
disk dismembering, displacing the stars from the disk. The impact of precession
on the star orbits is stronger when the stellar disk and the inner gas ring are
nearly coplanar. We speculate that the warm gas in the inner cavity might have
played a major role in the evolution of the clockwise disk.
