belt models. Taking the millimeter emission as the best tracer of the dust-producing planetesimals, the various inclination determinations are compatible with coplanarity with the planetary orbits, and with the star, although the uncertainties remain large enough to preclude drawing a firm conclusion.

If the planetesimal belt and planet orbits are coplanar, as suggested by the derived inclination angle, then we would also expect alignment of the position angle of the belt and the argument of ascending node of the planet orbits, $\Omega$. The @konopacky16 astrometric analysis indicates $\Omega$ lies in the range of 40 to $70\degr$ for low eccentricity solutions, for all four of the planets. The disk position angle of $35\fdg6^{+9.4}_{-10.1}$ determined from the joint analysis of the SMA and ALMA data is compatible with the low end of this range. Like the inclination, the disk position angles derived from millimeter and far-infrared emission are discrepant, with the latter yielding a higher value of $64\degr\pm3\degr$ [@matthews14]. Again, there may be a physical origin for this difference. The overlap of the millimeter constraint on the planetesimal belt position angle and the planetary argument of ascending node provides weak additional support for coalignment of these components.

Dynamical Constraints on the Mass 