2-PERIOD LIGHTCURVE OF 1994-AW(1) - INDICATION OF A BINARY ASTEROID

An analysis of the complex lightcurve of the Earth-approaching asteroi d 1994 AW(1) is presented. We have found that the lightcurve can be ex plained as the sum of two components having different periods, P-1 = 0 .4666 +/- 0.0005 day and P-2 = 0.104972 +/- 0.000006 day, confirming a nd refining the finding by S. Mottola et al, (Icarus 117, 62-70, 1995) , It is the first case of detection of a double-period lightcurve for a fast rotator. We present a hypothesis of an occulting/eclipsing bina ry asteroid that can explain the observed lightcurve character. The es timated ratio of the diameters of the secondary to the primary is 0.5: 1, the orbital period P = 2P(1), and the eccentricity is small, The ro tation of the primary is not synchronized with the orbital motion and has a period of P-1. The origin and evolution of the binary system may be related to close encounters with the Earth, as suggested by the th eory of W. F, Bottke and H. J. Melosh (Nature 281, 51-53, 1996). An al ternative hypothesis for 1994 AW, as a single body in the excited rota tion state requires further study, Since the relaxation time of the ex cited rotation is probably much shorter than the lifetime of the aster oid in its current orbit, it would require a relatively recent setting of the excited rotation, (C) 1997 Academic Press.