# Study of the plutino object (208996) 2003 AZ84 from stellar occultations: size, shape and topographic features

## TL;DR

This study uses stellar occultations to determine the size, shape, density, and topography of the plutino object (208996) 2003 AZ84, revealing a triaxial shape, low density, and a significant topographic feature.

## Contribution

First detailed shape and topography analysis of 2003 AZ84 using multiple stellar occultations, challenging previous oblate models and providing new physical parameters.

## Key findings

- 2003 AZ84 is a Jacobi triaxial ellipsoid with semi axes ~470x383x245 km.
- Density of 2003 AZ84 is approximately 0.87 g/cm³.
- A topographic feature possibly a chasm or depression was observed on its limb.

## Abstract

We present results derived from four stellar occultations by the plutino object (208996) 2003~AZ$_{84}$, detected at January 8, 2011 (single-chord event), February 3, 2012 (multi-chord), December 2, 2013 (single-chord) and November 15, 2014 (multi-chord). Our observations rule out an oblate spheroid solution for 2003~AZ$_{84}$'s shape. Instead, assuming hydrostatic equilibrium, we find that a Jacobi triaxial solution with semi axes $(470 \pm 20) \times (383 \pm 10) \times (245 \pm 8)$~km % axis ratios $b/a= 0.82 \pm 0.05$ and $c/a= 0.52 \pm 0.02$, can better account for all our occultation observations. Combining these dimensions with the rotation period of the body (6.75~h) and the amplitude of its rotation light curve, we derive a density $\rho=0.87 \pm 0.01$~g~cm$^{-3}$ a geometric albedo $p_V= 0.097 \pm 0.009$. A grazing chord observed during the 2014 occultation reveals a topographic feature along 2003~AZ$_{84}$'s limb, that can be interpreted as an abrupt chasm of width $\sim 23$~km and depth $> 8$~km or a smooth depression of width $\sim 80$~km and depth $\sim 13$~km (or an intermediate feature between those two extremes).