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We present a method for fitting orbit-superposition models to the kinematicsof discrete stellar systems when the available stellar sample has been filteredby a known selection function. The fitting method can be applied to any modelin which the distribution function is represented as a linear superposition ofbasis elements with unknown weights. As an example, we apply it to Fritz etal.'s kinematics of the innermost regions of the Milky Way's nuclear stellarcluster. Assuming spherical symmetry, our models fit a black hole of mass$M_\bullet=(3.76\pm0.22)\times10^6\,M_\odot$, surrounded by an extended mass$M_\star=(6.57\pm0.54)\times10^6\,M_\odot$ within 4 pc. Within 1 pc thebest-fitting mass models have an approximate power-law density cusp$\rho\propto r^{-\gamma}$ with $\gamma=1.3\pm0.3$. We carry out an extensiveinvestigation of how our modelling assumptions might bias these estimates:$M_\bullet$ is the most robust parameter and $\gamma$ the least. Internally thebest-fitting models have broadly isotropic orbit distributions, apart from abias towards circular orbits between 0.1 and 0.3 parsec.

Orbit-superposition models of discrete, incomplete stellar kinematics: application to the Galactic centre