Photometric study of Centaurs 10199 Chariklo (1997 CU26) and 1999 UG5

We present the results of visible broad band photometry of two Centaurs, 10199 Chariklo (1997 CU26) and 1999 UG(5) from data obtained at the 1.52 meter telescope of the National Astronomical Observatory at Calar Alto, Spain, during 2 separate runs in April 1999 and February 2000 and at the 1.5 meter telescope of the Sierra Nevada Observatory, Spain, in March of 1999. For Chariklo, the absolute magnitudes determined from the February 2000 data are found to be higher by about 0.27 mag than the average in the 1999 run. This may indicate long period rotational variability and possibly a G parameter higher than the assumed value of 0.15. From the best sampled R-lightcurve obtained in the February 2000 run, no short term rotational variability was found. The V- R colours for this object in all runs are similar to previously published values. For 1999 UG(5), colours were found to be very red: B - V = 0.88 +/- 0.18, V - R = 0.60 +/- 0.08 and R- I = 0.72 +/- 0.13. These results place this object in the group of the reddest known bodies in the Solar System. H-R and H-V are found to be 10.06 +/- 0.09 and 10.61 +/- 0.07 respectively, and its diameter is estimated to be on the order of 47 +/- 2 km.