Omicron Aquarii is late-type , Be shell star with a stable and nearly symmetric H \alpha emission line . We combine H \alpha interferometric observations obtained with the Navy Precision Optical Interferometer ( NPOI ) covering 2007 through 2014 with H \alpha spectroscopic observations over the same period and a 2008 observation of the system ’ s near-infrared spectral energy distribution to constrain the properties of o Aqr ’ s circumstellar disk . All observations are consistent with a circumstellar disk seen at an inclination of 75 \pm 3 ^ { \circ } with a position angle on the sky of 110 \pm 8 ^ { \circ } measured E from N. From the best-fit disk density model , we find that 90 % of the H \alpha emission arises from within 9.5 stellar radii , and the mass associated with this H \alpha disk is \sim 1.8 \times 10 ^ { -10 } of the stellar mass and the associated angular momentum , assuming Keplerian rotation for the disk , is \sim 1.6 \times 10 ^ { -8 } of the total stellar angular momentum . The occurrence of a central quasi-emission ( CQE ) feature in Mg ii \lambda 4481 is also predicted by this best-fit disk model and the computed profile compares successfully with observations from 1999 . To obtain consistency between the H \alpha line profile modelling and the other constraints , it was necessary in the profile fitting to weight the line core ( emission peaks and central depression ) more heavily than the line wings , which were not well reproduced by our models . This may reflect the limitation of assuming a single power-law for the disk ’ s equatorial density variation . The best-fit disk density model for o Aqr predicts that H \alpha is near its maximum strength as a function of disk density , and hence the H \alpha equivalent width and line profile change only weakly in response to large ( factor of \sim 5 ) changes in the disk density . This may in part explain the remarkable observed stability of o Aqr ’ s H \alpha emission line profile .