Discovery Announcement of Binary System 2016 AZ8


Range-Doppler radar images of near-Earth asteroid 2016 AZ8 with range resolution (vertical axis) of 7.5 m/pixel and Doppler frequency resolution (horizontal axis) of 0.03 Hz where (left) is the sequence of images over the almost 40 min of data and (right) is the first frame, obtained over about 3 min.

Discovery Announcement of Binary System Near-Earth Asteroid 2016 AZ8

A. K. Virkki, S. E. Marshall, F. C. F. Venditti, L. F. Zambrano Marin, Arecibo Observatory, University of Central Florida, and E. G. Rivera-Valentin, P. A. Taylor, Lunar and Planetary Institute, Universities Space Research Association, report that Arecibo (2380 MHz, 12.6 cm) range-Doppler radar images obtained on 2019 January 4.72 UT reveal near-Earth asteroid 2016 AZ8 is a binary system. Preliminary measurements of visible range extents in radar images with 7.5 m/pixel resolution suggest a rounded primary of diameter 420 ± 60 m and an elongated secondary 180 ± 30 m long. This implies a visual albedo of 4 ± 1% for an absolute magnitude of 21.0. The system was observed near maximum range separation along the line of sight at 420 ± 45 m, which is a lower bound on the mutual-orbit scale due to possible projection effects. Echo bandwidths place upper bounds on the rotation periods of the primary and secondary of 7 and 40 hours, also subject to projection effects. Further observations are encouraged; no more radar observations from Arecibo are possible this apparition. A projected separation comparable to the primary diameter and the slow projected rotation periods suggest the mutual-orbit plane of the system may have been inclined by tens of degrees relative to the line of sight during the observations. As such, observers should assume typical parameters for near-Earth binary systems of 2 to 4 hours for the primary rotation period and a mutual-orbit period between 12 and 24 hours.


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