Data Set Overview  :  We observed near-Earth Asteroid (8567) 1996 HW1 at the Arecibo Observatory on six dates in September 2008, obtaining radar images and spectra. By  combining these data with an extensive set of new lightcurves taken during 2008-2009 and with previously published lightcurves from 2005, we were  able to reconstruct the object's shape and spin state. 1996 HW1 is an  elongated, bifurcated object with maximum diameters of 3.8 x 1.6 x 1.5 km  and a contact-binary shape. It is the most bifurcated near-Earth asteroid  yet studied and one of the most elongated as well. The sidereal rotation  period is 8.76243 +/- 0.00004 h and the pole direction is within 5 degrees of ecliptic longitude and latitude (281, -31). Radar astrometry has  reduced the orbital element uncertainties by 27% relative to the a priori  orbit solution that was based on a half-century of optical data. Simple  dynamical arguments are used to demonstrate that this asteroid could have  originated as a binary system that tidally decayed and merged.   The shape model is presented as a faceted solid in Wavefront .obj format.  Also given are rendered .png images of the shape and tabulated rotation  state.

Confidence Level Overview  :  See table 3 of Magri et al., 2011 for formal model uncertainties. The  coordinate system is not precisely aligned to the center of mass and  moments of inertia. In principle, offsets could be physically meaningful,  but they are within the uncertainties for this model.