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Leucus from Lightcurves and Occultations The Planetary Science Journal, 1:73 (14pp), 2020 December https://doi.org/10.3847/PSJ/abb942 © 2020. The Author(s). Published by the American Astronomical Society. Convex Shape and Rotation Model of Lucy Target (11351) Leucus from Lightcurves and Occultations Stefano Mottola1 , Stephan Hellmich1, Marc W. Buie2 , Amanda M. Zangari2,4, Simone Marchi2, Michael E. Brown3, and Harold F. Levison2 1 Institute of Planetary Research, DLR Rutherfordstr. 2, D-12489 Berlin, Germany; [email protected] 2 Southwest Research Institute 1050 Walnut Street, Boulder, CO 80302, USA 3 California Institute of Technology 1200 E. California Boulevard, Pasadena, CA 91125, USA Received 2020 July 6; revised 2020 September 1; accepted 2020 September 15; published 2020 December 8 Abstract We report new photometric lightcurve observations of the Lucy Mission target (11351) Leucus acquired during the 2017, 2018, and 2019 apparitions. We use these data in combination with stellar occultations captured during five epochs to determine the sidereal rotation period, the spin axis orientation, a convex shape model, the absolute scale of the object, its geometric albedo, and a model of the photometric properties of the target. We find that Leucus is a prograde rotator with a spin axis located within a sky-projected radius of 3°(1σ) from J2000 Ecliptic coordinates (λ=208°, β=+77°) or J2000 Equatorial Coordinates (R.A.=248°,decl.=+58°). The sidereal period is refined to Psid=445.683±0.007 h. The convex shape model is irregular, with maximum dimensions of 60.8, 39.1, and 27.8 km. The convex model accounts for global features of the occultation silhouettes, although minor deviations suggest that local and global concavities are present. We determine a geometric albedo of pV=0.043±0.002. The derived phase curve supports a D-type classification for Leucus. Unified Astronomy Thesaurus concepts: Light curves (918); Stellar occultation (2135); Jupiter trojans (874); CCD photometry (208) Supporting material: machine-readable table 1. Introduction encounters and to complement the space-based measurements with data that are most efficiently acquired from the ground. Jupiter Trojans are a class of small objects trapped in the Jupiter This paper presents new lightcurve photometry of the Lucy L4 and L5 Lagrangian points. Their origin is still disputed, with target Leucus, which is used, together with the results of stellar the most likely scenarios falling into the categories (1) coeval occultation campaigns presented in a companion paper (Buie trapping of local planetesimals in the 1:1 mean motion resonance et al. 2020), to determine its convex shape, spin axis orientation, with accreting Jupiter as a consequence of drag or collisions albedo, size, sphere-integrated phase curve, and V–R color index. (Yoder 1979; Shoemaker et al. 1989) or (2) post-Jupiter-formation capture of scattered trans-Neptunian planetesimals following an episode of orbital chaos (Morbidelli et al. 2005) during the orbital 2. Leucus migration of the giant planets or as a consequence of the Jumping ( ) fi ( ) 11351 Leucus belongs to the Jupiter L4 Trojan swarm. Jupiter scenario as de ned in Nesvorný et al. 2013 . In either Radiometric measurements by the IRAS satellite reported a size case, Trojans are thought to be primitive objects that experienced and a geometric albedo of 42.2±4.0 km and 0.063±0.014, little thermal evolution and contain a considerable amount of respectively (Tedesco et al. 2004). Grav et al. (2012) reported a volatiles, which makes them close relatives to cometary nuclei. size and an albedo of 34.155±0.646 km and 0.079±0.013, With a launch planned for 2021 October, Lucy is the thirteenth fi fi respectively, based on Wide- eld Infrared Survey Explorer NASA mission of the Discovery Program and will be the rst one (WISE) radiometry. Levison & Lucy Science Team (2016) to explore the Jupiter Trojan System. Its trajectory is designed to tentatively classified Leucus as belonging to the D taxonomic flybyfive Trojans—one of which, (617) Patroclus is an equal-size ( ) — type based on its visible spectral slope Roig et al. 2008 .No binary system distributed over the two Lagrangian clouds. The collisional family membership has been proposed as of today. encounter with Leucus is currently planned for 2028 June 18. A French et al. (2013) first realized from lightcurve data that coordinated effort has been initiated to support the mission with a Leucus is a very slow rotator, although they identified an systematic program of ground-based observations of the mission incorrect period of 515h. Buie et al. (2018), using photometric targets aiming at characterizing their dynamical, physical, observations acquired during the 2016 apparition, combined rotational, and photometric properties. The goal is to inform the ( ) fi fi with observations by French 2013 , determined a rm rotation mission design in order to maximize the scienti creturnofthe period of 445.732±0.021h. They also estimated a geometric 4 albedo of 0.047 based on the WISE diameter and on an average Amanda Zangari is currently an MIT Lincoln Laboratory employee. No color index for D-type asteroids. laboratory funding or resources were used to produce the results/findings reported in this publication. 3. Observations and Data Reduction Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further The new Leucus photometric observations reported in this distribution of this work must maintain attribution to the author(s) and the title paper were performed during its 2017, 2018, and 2019 apparitions of the work, journal citation and DOI. by using 1.0 m telescopes from the Las Cumbres Observatory 1 The Planetary Science Journal, 1:73 (14pp), 2020 December Mottola et al. Table 1 Observational Circumstances λ ( ) β Date λβ α r Δ PAB Band Observatory Observers (UT)(° J2000)(°)(au)(au)(° J2000) 2017 May 1.1 287.4 +5.7 9.683 5.507 1 5.032 0 282.5 +5.5 RC 493 SH, SMo 2017 May 2.1 287.4 +5.8 9.616 5.506 7 5.017 5 282.6 +5.5 RC 493 SH, SMo 2017 May 20.1 287.0 +6.3 7.887 5.500 5 4.774 5 283.0 +5.9 RC 493 SH, SMo 2017 May 28.1 286.5 +6.6 6.841 5.497 7 4.685 2 283.1 +6.1 RC 493 SMo, SH 2017 May 30.1 286.3 +6.6 6.550 5.497 0 4.664 6 283.1 +6.1 RC 493 SMo, SH 2017 May 31.0 286.3 +6.6 6.408 5.496 6 4.655 1 283.1 +6.1 RC 493 SMo, SH 2017 Jul 16.4 281.0 +7.6 2.738 5.479 8 4.491 4 282.2 +6.9 r′ Q64 MWB, AZ 2017 Jul 17.0 280.9 +7.6 2.833 5.479 5 4.493 2 282.1 +6.9 r′ W86 MWB, AZ 2017 Jul 17.3 280.9 +7.6 2.882 5.479 4 4.494 2 282.1 +6.9 r′ W85 MWB, AZ 2017 Jul 17.6 280.8 +7.6 2.933 5.479 3 4.495 2 282.1 +6.9 r′ Q63 MWB, AZ 2017 Jul 17.9 280.8 +7.6 2.980 5.479 2 4.496 2 282.1 +6.9 r′ K93 MWB, AZ 2017 Jul 18.2 280.8 +7.6 3.031 5.479 1 4.497 3 282.1 +6.9 r′ W86 MWB, AZ 2018 Jun 11.1 318.3 +11.1 9.382 5.339 4 4.745 1 313.5 +10.5 RC 493 SH, SMo 2018 Jul 9.1 316.6 +12.1 5.829 5.326 3 4.437 9 313.8 +11.1 V 493 SH, SMo 2018 Jul 15.0 316.0 +12.2 4.895 5.323 6 4.394 7 313.8 +11.2 V 493 SH, SMo 2018 Sep 4.9 309.8 +12.5 6.171 5.299 0 4.436 2 312.8 +11.5 V 493 SH, SMo 2018 Aug 6.9 313.2 +12.7 2.406 5.312 7 4.318 6 313.3 +11.5 RC 493 SH, SMo 2018 Aug 8.0 313.1 +12.7 2.432 5.312 3 4.318 7 313.3 +11.5 RC 493 SH, SMo 2018 Aug 9.0 312.9 +12.7 2.475 5.311 8 4.319 2 313.3 +11.5 RC 493 SH, SMo 2019 Nov 9.1 342.2 +12.6 10.103 5.101 6 4.597 6 347.3 +12.0 VR G80 MWB 2019 Nov 10.1 342.2 +12.6 10.181 5.101 2 4.611 2 347.4 +12.0 VR G80 MWB 2019 Nov 11.1 342.2 +12.5 10.257 5.100 8 4.624 9 347.4 +12.0 VR G80 MWB 2019 Nov 12.1 342.2 +12.5 10.329 5.100 4 4.638 7 347.5 +11.9 VR G80 MWB 2019 Nov 24.1 342.6 +12.0 10.962 5.095 5 4.812 3 348.2 +11.7 VR G80 MWB Note. This table is an excerpt. The observational circumstances for all of the observation nights are reported in the online material. λ and β are the topocentric ecliptic longitude and latitude of the target, respectively. α is the solar phase angle, r is the heliocentric distance, and Δ is the topocentric range of Leucus. λ and β (PAB) are the topocentric ecliptic longitude and latitude of the phase angle bisector, as defined in Harris et al.
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