Size and Shape of Trojan Asteroid Diomedes from Its Occultation and Photometry

✍ Scribed by Isao Satō; Lenka Šarounová; Hideo Fukushima

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 225 KB
• Volume: 145
• Category: Article
• ISSN: 0019-1035
• DOI: 10.1006/icar.1999.6316

✦ Synopsis

The first Trojan asteroid occultation, the occultation of HIP 014402A by ( 1437) Diomedes, was successfully observed from Japan on November 7, 1997. From its occultation timings at six sites including two video observations, an elongated occultation silhouette of (180 ± 28 km) × (96 ± 5 km), at position angle PA = 150 ± 4 • was revealed. Follow-up photometry of Diomedes obtained at Ondřejov on November 10 and 11 and at Mitaka on November 18, 19, and 24 revealed that its rotation period is 1.019 ± 0.004 days, its amplitude of light variation is 0.70 ± 0.15 mag, and its rotational phase at the occultation was almost at a minimum of the lightcurve. From these observations, a probability distribution ellipsoidal model for Diomedes is derived. It shows that two families of ellipsoidal models are possible. One is a triaxial ellipsoid of b/a ≈ 0.55; the other is a rather prolate ellipsoid of b/a ≈ 0.4, c/b ≈ 1. Possible orientation of the rotation axis is very restricted to two great circles on the celestial sphere. Mean lengths of the three principal axes of the model ellipsoid are (284 ± 61 km) × (126 ± 35 km) × (65 ± 24 km), i.e., approximately a : b : c ≈ 4 : 2 : 1.