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J. L. Margot, M. E. Brown (California Institute of Technology)
A companion to asteroid 22 Kalliope was discovered at the 10-m Keck II telescope on Mauna Kea on UT Aug. 29.6, with follow-up observations on Aug 31.6 and Sep 1.6 [1]. The satellite was also observed by W. J. Merline and collaborators at the Canada-France-Hawaii Telescope on UT Sep 2.6 and 3.6 [2]. We have since then obtained additional data on several nights with the 5-m Palomar telescope in order to fully characterize the orbital parameters of the system.
At this preliminary stage in the data analysis, our combined Keck and Palomar data are consistent with an orbital period of about 3.6 days and a semi-major axis of about 1100 km (12 primary radii). If correct, these values and the IRAS diameter of 181 +/- 4.6 km [3] imply a density for 22 Kalliope of roughly 2.5 +/- 0.3 g/cm3. This suggests that Kalliope, an M-class asteroid, may not be metallic in composition.
87 Sylvia is a P-type asteroid with a diameter of 271 +/- 13.3 km [3]. Its satellite, with a diameter about 1/20 that of the primary, was discovered with the Keck II telescope at a separation of 0.6" from the primary [4]. We tracked the system's orbital motion at Keck during 5 consecutive nights. The orbital separation is roughly 10 primary radii and the orbital period is 3.6 days. This implies a density for the primary of 1.62 +/- 0.3 g/cm3, with the uncertainty on the diameter accounting for most of the error bars. The satellite of 87 Sylvia was also detected on HST images [5].
Preliminary results on the frequency and characteristics of asteroid binaries in the main belt will be presented at the meeting.
[1] J. L. Margot and M. E. Brown (2001), IAU Circ. No. 7703. [2] W. J. Merline, F. Menard, L. Close, C. Dumas, C. R. Chapman, D. C. Slater (2001), IAU Circ. No. 7703. [3] E. F. Tedesco (1992), PL-TR-92-2049, Hanscom Air Force Base. [4] M. E. Brown and J. L. Margot (2001), IAU Circ. No. 7588. [5] A. Storrs, F. Vilas, R. Landis, E. Wells, C. Woods, B. Zellner, M. Gaffey (2001), IAU Circ. No. 7590.