We present line-of-sight stellar velocity distributions of elliptical galaxy NGC 821 obtained to approximately 100 \arcsec ( over 2 effective radii ) with long-slit spectroscopy from the Hobby-Eberly Telescope .
Our measured stellar line-of-sight velocity distributions are larger than the planetary nebulae measurements at similar radii .
We fit axisymmetric orbit-superposition models with a range of dark halo density profiles , including two-dimensional kinematics at smaller radii from SAURON data .
Within our assumptions , the best-fitted model gives a total enclosed mass of 2.0 \times 10 ^ { 11 } M _ { \sun } within 100 \arcsec , with an accuracy of 2 % ; this mass is equally divided between halo and stars .
At 1 R _ { e } the best-fitted dark matter halo accounts for 13 \% of the total mass in the galaxy .
This dark halo is inconsistent with previous claims of little to no dark matter halo in this galaxy from planetary nebula measurements .
We find that a power-law dark halo with a slope 0.1 is the best-fitted model ; both the no dark halo and NFW models are worse fits at a greater than 99 % confidence level .
NGC 821 does not appear to have the expected dark halo density profile .
The internal moments of the stellar velocity distribution show that the model with no dark halo is radially anisotropic at small radii and tangentially isotropic at large radii , while the best-fitted halo models are slightly radially anisotropic at all radii .
We test the potential effects of model smoothing and find that there are no effects on our results within the errors .
Finally , we run models using the planetary nebula kinematics and assuming our best-fitted halos and find that the planetary nebulae require radial orbits throughout the galaxy .