Occultation/Eclipse Events in Binary Asteroid 1991 VH

Abstract

We present the results of photometric observations of the Apollo asteroid 1991 VH. Its lightcurve consists of two components: the first is the rotational lightcurve with periodPs= (0.109327 ± 0.000003) d and amplitude 0.09 mag, while the second, with periodPl= (1.362 ± 0.001) d, shows two minima with depth 0.16–0.19 mag, each with a duration of about 0.10 d, and little or no variation at phases between them. We present a model of the occulting/eclipsing binary asteroid with the secondary-to-primary diameter ratiods/dp= 0.40 that explains the observed lightcurve. In this model, the primary's rotation is not synchronized with the orbital motion and produces the short-period lightcurve component (Ps). The orbital period isPl. The mutual orbit's semimajor axis is estimated to bea= (2.7 ± 0.3)dp; the eccentricity is 0.07 ± 0.02. The similarity between the lightcurve of 1991 VH and those of 1994 AW1(Pravec and Hahn,Icarus127, 431, 1997) and (3671) Dionysus (Mottolaet al.1997,IAU Circular6680) suggests that binary asteroids may be common among near-Earth asteroids. Based on the three known cases, we tentatively derive some typical characteristics of this new class of asteroids. They are mostly consistent with the hypothesis that binary asteroids are generated by tidal disruptions of weak, gravitationally bound aggregates (so-called “rubble piles”) during encounters with the Earth (Bottke and Melosh,Nature281, 51, 1996). A possible relationship between the population of binary asteroids and the belt of small near-Earth asteroids is discussed.