On the possible binarity of asteroid 21 Lutetia from analysis of simultaneous BVR observations

We obtained ～1000 B, V, and R magnitude measurements for asteroid 21 Lutetia quasi-simultaneously with the digital TV system of a 0.5-m MTM-500 meniscus telescope from November 3 through November 11, 2004. We performed a frequency analysis of the B-V and V-R color indices and the V magnitudes based on data averaged over five measurements, which provided an accuracy of the mean color indices and magnitudes of ～0. ^m 005 and 0. ^m 08, respectively. Our analysis of the color indices showed the absence of the known period, 0.^d3405 (8.^h172), and the presence of several periods at a confidence level of 7–10 σ, including P ₀ = 2.^h93 (1/P = 8.17c/d) and its alias 2.^h64 (1/P = 9.17c/d). Our analysis of the V-band data revealed the periods P ₁ = 0.^d70 and P ₂ = 3.^d20; both periods yielded double-peaked light curves with amplitudes of 0. ^m 12 and 0. ^m 10. The first period is probably the rotation period of the main component, while the second period may be equal to the orbital period of the satellite with one side facing the main body. Another model of the asteroid is also possible: P ₀ = 2.^h93 is the rotation period of the main body, P ₁ = 0.^d70 is the orbital period of the synchronous satellite, and P ₂ = 3.^d20 is the precession period.