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The Complex Rotational Light Curve of (385446) Manwë–Thorondor, a Multicomponent Eclipsing System in the Kuiper Belt

2019; Institute of Physics; Volume: 159; Issue: 1 Linguagem: Inglês

10.3847/1538-3881/ab59d4

1538-3881

D. Rabinowitz, Susan D. Benecchi, W. M. Grundy, A. Verbiscer, Audrey Thirouin,

Stellar, planetary, and galactic studies

Abstract Kuiper Belt Object (385446) Manwë–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 4 m SOAR and the 8.1 m Gemini South telescopes at Cerro Pachón, Chile, and Lowell Observatory’s 4.3 m Discovery Channel Telescope at Happy Jack, Arizona. These dates overlap the uncertainty range (±0.5 day) for four inferior events (Thorondor eclipsing Manwë). We clearly observe variability for the unresolved system with a double-peaked period 11.88190 ± 0.00005 hr and ∼0.5 mag amplitude together with much longer-term variability. Using a multicomponent model, we simultaneously fit our observations and earlier photometry measured separately for Manwë and Thorondor with the Hubble Space Telescope . Our fit suggests Manwë is bilobed, close to the “barbell” shape expected for a strengthless body with density ∼0.8 g cm −3 in hydrostatic equilibrium. For Manwë, we thereby derive maximum width to length ratio ∼0.30, surface area equivalent to a sphere of diameter 190 km, geometric albedo 0.06, mass 1.4 × 10 18 kg, and spin axis oriented ∼75° from Earth’s line of sight. Changes in Thorondor’s brightness by ∼0.6 mag with a ∼300 day 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.