A possible dynamically Cold Classical contact binary: (126719) 2002 CC249

Abstract

Images of the Kuiper belt object (126719) 2002 CC249 obtained in 2016 and 2017 using the 6.5m Magellan-Baade Telescope and the 4.3m Discovery Channel Telescope are presented. A lightcurve with a periodicity of 11.87+/-0.01 h and a peak-to-peak amplitude of 0.79+/-0.04 mag is reported. This high amplitude double-peaked lightcurve can be due to a single elongated body, but it is best explained by a contact binary system from its U-/V-shaped lightcurve. We present a simple full-width-at-half-maximum (FWHM) test that can be used to determine if an object is likely a contact binary or an elongated object based on its lightcurve. Considering that 2002 CC249 is in hydrostatic equilibrium, a system with a mass ratio qmin=0.6, and a density \rho min=1gcc, or less plausible a system with qmax=1, and \rho max=5gcc can interpret the lightcurve. Assuming a single Jacobi ellipsoid in hydrostatic equilibrium, and an equatorial view, we estimate \rho = 0.34gcc, and a/b=2.07. Finally, we report a new color study showing that 2002 CC249 displays an ultra red surface characteristic of a dynamically Cold Classical trans-Neptunian object.