Study of the Plutino Object (208996) 2003 AZ84 from Stellar Occultations: Size, Shape, and Topographic Features

We present results derived from four stellar occultations by the plutino object (208996) 2003 AZ₈₄, detected on 2011 January 8 (single-chord event), 2012 February 3 (multi-chord), 2013 December 2 (single-chord), and 2014 November 15 (multi-chord). Our observations rule out an oblate spheroid solution for 2003 AZ₈₄'s shape. Instead, assuming hydrostatic equilibrium, we find that a Jacobi triaxial solution with semiaxes (470+/- 20)× (383+/- 10)× (245+/- 8) km can better account for all our occultation observations. Combining these dimensions with the rotation period of the body (6.75 hr) and the amplitude of its rotation light curve, we derive a density ρ =0.87+/- 0.01 g cm^-3, a geometric albedo {p}_V=0.097+/- 0.009. A grazing chord observed during the 2014 occultation reveals a topographic feature along 2003 AZ₈₄'s limb, which can be interpreted as an abrupt chasm of width ∼23 km and depth > 8 km, or a smooth depression of width ∼80 km and depth ∼13 km (or an intermediate feature between those two extremes).