SPIN VECTOR, SHAPE, AND SIZE OF THE AMOR-ASTEROID(6053) 1993-BW3

We present an analysis of our observations of near-Earth asteroid (605 3) during its long-lasting apparition from July 1995 to February 1996. Nineteen R lightcurves were obtained at intervals not exceeding 36 da ys. The derivation of the asteroid's spin vector is based on a new imp lementation of the epoch method. The times of minima of the second har monics of the Fourier series fits to the lightcurves are taken as the reference times. The most probable pole solution obtained is (175 degr ees, -9 degrees) in J2000 ecliptic coordinates, with formal errors of 5 degrees and 3 degrees, respectively. The sidereal rotation period is 2.573419 +/- 0.000014 hr. There exists another, less probable solutio n of (359 degrees, -26 degrees, 2.573986 hr), which we cannot rule out with certainty; however, it gives also a poorer mean magnitude-aspect dependence than that for the first, most probable solution; this lead s us to conclusion that the most probable solution is the true one. Th e shape of the asteroid can be approximated by a triaxial ellipsoid si milar to an oblate spheroid, with ratios of its major axes a/b = 1.08 +/- 0.04 and b/c approximate to 1.5 or greater. Combining thermal obse rvations made on 1995 August 12 with the visual photometric results, a range of geometric albedo p(v) of 0.11-0.25 is obtained together with a mean equatorial diameter of 3.3 +/- 0.6 km. The derived range of al bedo and the measured colors (V - R = 0.48 +/- 0.02, R - I = 0.35 +/- 0.02, and B - V = 0.99 +/- 0.05) are consistent with an S-type classif ication. Taking a geometric albedo of 0.16 typical for this class, the axes of the ellipsoid best approximating the asteroid's shape are 2a = 3.5 km, 2b = 3.2 km, and 2c approximate to 2 km. The high power in t he first harmonic observed in the lightcurves is due to a surface irre gularity (deviation from the ellipsoid figure), rather than a hemisphe rical albedo variegation. (C) 1997 Academic Press.