Observations of the Centaur 1999 UG 5 : Evidence of a Unique Outer Solar System Surface

Abstract

The outer solar system body 1999 UG5 is a Centaur of medium brightness and slightly redder color when compared to other Centaurs. Similar to at least 1/5 of the known Centaurs, it is a Saturn-crosser with a mean orbital distance between Saturn and Uranus. We present optical photometry data and near-IR spectra obtained during 2000 September, November, and December. We find a rotation period of 13.41+/-0.04 hr with an amplitude of 0.102+/-0.005 mag and a phase curve with a Lumme-Bowell G value of -0.13+/-0.02. BVRI colors are reported, and they confirm the red spectral gradient observed previously. Our spectra reveal that this redward slope extends into near-IR wavelengths and indicates possible localized differences in the surface composition.