37th DPS Meeting, 4-9 September 2005
Session 52 TNOs and Centaurs
Oral, Thursday, September 8, 2005, 2:00-3:50pm, Law LG19

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[52.04] Kuiper Belt Binaries: Masses, Colors, and a Density

J. L. Margot (Cornell University), M. E. Brown (Caltech), C. A. Trujillo (Gemini), R. Sari (Caltech), J. A. Stansberry (U of Arizona)

We report results from our Hubble Space Telescope (HST) program designed to characterize the orbital and physical properties of six confirmed KBO binaries. The orbital parameters provide unambiguous mass measurements that place strong constraints on the density-albedo parameter space for those KBOs (Margot et al., BAAS 36, 2004). The masses combined with size determinations yield KBO densities.

Based on point-spread function (PSF) fitting to our ACS/HRC images, we find that the primary/secondary flux ratios remain remarkably constant over long time intervals, suggesting that at least a few of the KBO binary components have no appreciable lightcurve (Table 1). This fact makes it easier to apportion the total system mass to individual components. A notable exception is 1997 CQ29 where the flux variations are so large that it is difficult to distinguish the primary from the secondary.

We also present color differences based on the flux measured in HST's F606W and F814W filters. Although these measurements are restricted to one HST visit per target, the relative similarity of the primary and secondary color differences suggests that the components have similar colors. This provides a powerful constraint on binary KBO formation mechanisms. Colors for 1999 TC36 are expected before the meeting.

Our mass for 1999 TC36 combined with the Spitzer size (Stansberry et al., this meeting) yields a density in the 0.5-0.8 g/cm3 range.

2000 CF105
1.96 ± 5%
1999 TC36
7.15 ± 2%
1998 SM165
9.02 ± 14%
2001 QC298
1.50 ± 10%
1997 CQ29
0.96 ± 35%

Table 1. Fp/Fs: Primary to secondary flux ratio; F6-F8: color difference in HST's F606W and F814W filters [magnitude units].

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