  We present J, H, CH_4 short (1.578 micron), CH_4 long (1.652 micron) and
K_s-band images of the dust ring around the 10 Myr old star HR 4796 A obtained
using the Near Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1
meter Telescope. Our images clearly show for the first time the position of the
star relative to its circumstellar ring thanks to NICI's translucent focal
plane occulting mask. We employ a Bayesian Markov Chain Monte Carlo method to
constrain the offset vector between the two. The resulting probability
distribution shows that the ring center is offset from the star by 16.7+/-1.3
milliarcseconds along a position angle of 26+/-3 degrees, along the PA of the
ring, 26.47+/-0.04 degrees. We find that the size of this offset is not large
enough to explain the brightness asymmetry of the ring. The ring is measured to
have mostly red reflectivity across the JHK_s filters, which seems to indicate
micron-sized grains. Just like Neptune's 3:2 and 2:1 mean-motion resonances
delineate the inner and outer edges of the classical Kuiper Belt, we find that
the radial extent of the HR 4796 A and Fomalhaut rings could correspond to the
3:2 and 2:1 mean-motion resonances of hypothetical planets at 54.7 AU and 97.7
AU in the two systems, respectively. A planet orbiting HR 4796 A at 54.7 AU
would have to be less massive than 1.6 Mjup so as not to widen the ring too
much by stirring.
