Simultaneous visible-near IR photometric study of Kuiper Belt Object surfaces with the ESO/Very Large Telescopes

Abstract

We present simultaneous visible-near-IR (BVRIJHK) photometry of 8 Kuiper belt objects (KBOs) and 4 Centaurs. The observations were carried out using two 8m-units of the ESO/Very Large Telescope operated simultaneously on November 29 and 30, 2000. The KBOs displayed linear reflectivity spectra in the optical with a wide range of slopes from neutral (solar) to very red. In most cases, the reflectivity spectra are linear from B to J bands. We notice a change of regime in the spectra which flatten toward the H and K bandpasses. (33128) 1998 BU 48 even has a significantly negative H - K value. Only (54598) 2000 QC 243 does not flatten in the infra-red. (24835) 1995 SM 55 has a noticeably blue spectrum in the near-lR which might be indicative of water ice absorption features. We also present an empirical model for KBO surface evolution, based on models from Luu & Jewitt (1996) and Stern (1995), in which surface colors evolve because of collisions. In the model presented here we propose that cometary activity can refresh the surface. This model predicts that (1) small (e.g. «80 km in radius) KBOs should have color variations with rotation, (2) the larger objects should display uniform colors, (3) there should be no color dependence with inclination for objects > 100 km in radius, and (4) very distant KBOs are fully irradiated.