DPS Pasadena Meeting 2000, 23-27 October 2000
Session 13. Asteroids II - Discovery and Dynamics
Oral, Chairs: W. Merline, J. Burns, Tuesday, 2000/10/24, 8:30-10:00am, C106

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[13.06] Discovery of Companions to Asteroids 762\thinspace Pulcova and 90\thinspace Antiope by Direct Imaging

W.J. Merline (SwRI), L.M. Close (ESO, U.~Arizona), C. Dumas (JPL), J.C. Shelton (Mt.~Wilson Obs.), F. Menard (CFHT), C.R. Chapman, D.C. Slater (SwRI)

We present images of two asteroid companions from adaptive optics (AO) observations. These detections bring to four the number of binary systems ever imaged, the previous discoveries being 243\thinspace Ida/Dactyl by Galileo in 1993 (Belton et al.\/ 1995, Nature 374, 785) and 45\thinspace Eugenia/Petit-Prince in 1998 (Merline et al.\/ 1999, Nature 401, 565).

A satellite of 762\thinspace Pulcova was discovered on 2000 Feb 22 UT at the Canada-France-Hawaii Telescope (CFHT) and was later confirmed by additional observations at CFHT and Keck II. The satellite is about 4 mag fainter than the primary and our fit to the orbit indicates that it was inclined approximately 60\thinspace deg to the line-of-sight, with a semi-major axis of 800\thinspace km (0.6\arcsec) and a period of 4.0 days. We derive a density for this FC-type primary of 1.8\thinspace g\thinspace cm-3, higher than our nominal value of 1.2\thinspace g\thinspace cm-3 for F-type Eugenia.

On 2000 Aug 10 UT, Keck AO observations revealed that the C-type 90\thinspace Antiope is a double asteroid, with similar-sized components, separated by only 170\thinspace km (0.12\arcsec), with a brightness difference of less than 0.1\thinspace mag. The co-orbiting pair was observed on 6 consecutive nights and was found to have an orbital period of about 16.5 hours, consistent with the established photometric ``rotation" period. While we cannot rule out a very thin bridge of material connecting the two, we show that it is not similar to the dumbbell-shaped 216\thinspace Kleopatra reported by Ostro et al. 2000 (Science 288, 836). The two components are clearly separated in the raw images, with a contrast consistent with the PSF. We acquired similar images of Kleopatra before, during, and after the radar observations of Ostro et al. Our Kleopatra images show a bridge connecting the two components, but such a bridge is absent in our Antiope images.

This program is funded by NSF and NASA and uses CFHT (French time), Keck Observatory (NASA time), and Mt. Wilson Observatory.

The author(s) of this abstract have provided an email address for comments about the abstract: merline@boulder.swri.edu

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