Optical Photometrical Observations of 3C273

The quasar 3C273 is one of selected targets in our monitoring program. In this paper, we present the optical V, R. and I photometric observations done with the 1.56 m telescope at the Shanghai Astronomical Observatory (ShAO) from 2000 to 2008. Our observations indicate that the variations in the three bands are Delta I = 1.04 +/- 0.14 mag, Delta R = 1.30 +/- 0.15mag and Delta V = 1.42 +/- 0.20 mag, a micro-variation of 0.18 mag over 2.1hrs is detected in R band. The color indices are in the ranges: V-R = 0.09 to 0.55, V-I = 0.33 to 1.13, and R-I = 0.12 to 0.73, and their averages are: V-R = 0.30 +/- 0.10,V - I = 0.73 +/- 0.16, R - I = 0.42 +/- 0.12.