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Description
Kuiper Belt Object (385446) Manwe-Thorondor is a multiobject system with mutual events predicted to occur from 2014 to 2019. To detect the events, we observed the system at 4 epochs (UT 2016 August 25 and 26, 2017 July 22 and 25, 2017 November 9, and 2018 October 6) in g, r, and VR bands using the 4m SOAR and the 8.1m Gemini South telescopes at Cerro Pachon, Chile, and Lowell Observatory's 4.3m Discovery Channel Telescope at Happy Jack, Arizona. These dates overlap the uncertainty range (±0.5 day) for four inferior events (Thorondor eclipsing Manwe). We clearly observe variability for the unresolved system with a double-peaked period 11.88190±0.00005hr and ∼0.5mag amplitude together with much longer-term variability. Using a multicomponent model, we simultaneously fit our observations and earlier photometry measured separately for Manwe and Thorondor with the Hubble Space Telescope. Our fit suggests Manwe is bilobed, close to the "barbell" shape expected for a strengthless body with density ∼0.8g/cm<SUP>3</SUP> in hydrostatic equilibrium. For Manwe, we thereby derive maximum width to length ratio ∼0.30, surface area equivalent to a sphere of diameter 190km, geometric albedo 0.06, mass 1.4x1018kg, and spin axis oriented ∼75deg from Earth's line of sight. Changes in Thorondor's brightness by ∼0.6mag with a ∼300day period may account for the system's long-term variability. Mutual events with unexpectedly shallow depth and short duration may account for residuals to the fit. The system is complex, providing a challenging puzzle for future modeling efforts.
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