| Résumé | Using the high-cadence lightcurves collected from the FOSSIL survey, rotation periods of 17 small (diameter 1 km < D < 3 km) Hilda asteroids (hereinafter Hildas) were obtained. Combined with the previously measured rotation periods of Hildas, a spin-rate limit appears at around 3 hr. Assuming rubble-pile structures for the Hildas, a bulk density of ∼1.5 g cm⁻³ is required to withstand this spin-rate limit. This value is similar to that of the C-type asteroids (1.33 g cm⁻³) and higher than the ∼1 g cm⁻³ bulk density of the Jupiter Trojans. This suggests that the Hildas population may contain more C-type asteroids than expected, and the limit at 3 hr simply reflects the spin-rate limit for C-type asteroids. In addition, a Hilda superfast rotator was found, which has a rotation period of 1.633 hr and an estimated diameter of 0.7 km. This object is unlikely to be explained by a rubble-pile or monolithic structure. |
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