Physical Characterization of the Binary Edgeworth—Kuiper Belt Object 2001 QT₂₉₇

Abstract

Following our discovery of 2001 QT₂₉₇ as the second known binary Edgeworth—Kuiper Belt Object (EKBO) in October of 2001 [IAUC 7733], we have carried out additional high spatial resolution ground based imaging in October and November of 2001 and July, August, and September of 2002. Using the Raymond and Beverly Sackler Magellan Instant Camera (MagIC) on the Baade and Clay 6.5 m telescopes at Las Campanas Observatory in Chile, we have obtained accurate astro-metric and photometric measurements in the Sloan r′,i′, and g′ filters. Superb seeing conditions and PSF fitting allow an accurate determination of the binary component separation and position angle over time as well as a detailed study of color and temporal variability of the individual components. Here we present a physical characterization of the individual components of 2001 QT₂₉₇ based on these astrometric, color and variability measurements. We find the primary to exhibit colors about 0.3 magnitudes redder than solar with no evidence for variability. The secondary component, however, exhibits strong variability (~0.6 magnitudes) with a best fit period of 4.7526 ± 0.0007 h for a single peak lightcurve or 9.505 ± 0.001 h for a dual peaked lightcurve. The colors measured for the secondary also suggest variability. Based on a preliminary orbit fit for the pair using observations spanning a one year arc, we are able to estimate a system mass of ~ 3.2 × 10¹⁸ kg and provide constraints to the surface albedo of 9–14% for assumed densities between 1 and 2 g/cm³.