BVR photometry of Centaur objects 1995 GO, 1993 HA(2), and 5145 Pholus

We present B, V, and R band photometry for three of the six known Centaur objects. We have measured V-R colors of 0.47+/-0.04 and 0.77+/-0.05 for the Centaurs 1995 GO and 1993 HA(2), respectively, as well as a B-V color of 0.75+/-0.04 for 1995 GO. We have measured B-V and V-R colors for the Centaur 5145 Pholus that closely agree with previous measurements in the literature. We have found that the four Centaurs with known colors can be separated into two groups, one group with near solar colors (2060 Chiron and 1995 GO) and the other with very red colors (5145 Pholus and 1993 HA(2)). Centaurs with solar colors may have surfaces rich in icy, primitive, carbonaceous chondrite like material while Centaurs that have very red surfaces may have icy surfaces rich in complex carbon bearing molecules. The differences in the surfaces of Centaurs may result from differences in their primordial composition. Perhaps, 5145 Pholus and 1993 HA, had higher initial concentrations of simple ice components (e.g., CH4) than 2060 Chiron and 1995 GO that upon cosmic ray or solar wind bombardment produced larger amounts of red colored complex organic molecules. Alternatively, Centaurs may have originated with similar initial compositions and thermal processing and coma formation may have altered the surface composition and hence the color of Centaurs closer to the Sun, 1995 GO (perihelion distance, q=6.85 AU) and 2060 Chiron (q=8.45 AU), but not the composition and hence the red color of Centaurs farther from the Sun, 5145 Pholus (q=8.68 AU) and 1993 HA(2) (q=11.83 AU). (C) 1997 American Astronomical Society.